ffmpeg结构体（14）-之AVOption与AVClass上

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AVOption与AVClass

- 1、AVOption的数据结构与定义
- 2、AVClass数据结构及其定义
- - 2.1 AVFormatContext 中的AVClass
  - 2.2AVFormatContext 中的AVClass
  - 2.3AVFrame中的AVClass
- 3、AVClass有关的API
- 4、参考文献

AVOption用于在FFmpeg中描述结构体中的成员变量。它最主要的作用可以概括为两个字：“赋值”。一个AVOption结构体包含了变量名称，简短的帮助，取值等等信息。

所有和AVOption有关的数据都存储在AVClass结构体中。如果一个结构体（例如AVFormatContext或者AVCodecContext）想要支持AVOption的话，它的第一个成员变量必须是一个指向AVClass结构体的指针。该AVClass中的成员变量option必须指向一个AVOption类型的静态数组

1、AVOption的数据结构与定义

AVOption是用来设置FFmpeg中变量的值的结构体。AVOption的特点就在于它赋值时候的灵活性。AVOption可以使用字符串为任何类型的变量赋值。AVOption将赋值“归一化”了，统一使用字符串赋值。例如给int型变量qp设定值为20，通过AVOption需要传递进去一个内容为“20”的字符串。
此外，AVOption中变量的名称也使用字符串来表示。结合上面提到的使用字符串赋值的特性，我们可以发现使用AVOption之后，传递两个字符串（一个是变量的名称，一个是变量的值）就可以改变系统中变量的值。

除了可以对FFmpeg常用结构体AVFormatContext，AVCodecContext等进行赋值之外，还可以对它们的私有数据priv_data进行赋值。这个字段里通常存储了各种编码器特有的结构体。而这些结构体的定义在FFmpeg的SDK中是找不到的。

例如使用libx264进行编码的时候，通过AVCodecContext的priv_data字段可以对X264Context结构体中的变量进行赋值，设置preset，profile等。使用libx265进行编码的时候，通过AVCodecContext的priv_data字段可以对libx265Context结构体中的变量进行赋值，设置preset，tune等。

/**
 * AVOption
 */
typedef struct AVOption {
    const char *name;

    /**
     * short English help text
     * @todo What about other languages?
     */
    const char *help;

    /**
     * The offset relative to the context structure where the option
     * value is stored. It should be 0 for named constants.
     */
    int offset;
    enum AVOptionType type;

    /**
     * the default value for scalar options
     */
    union {
        int64_t i64;
        double dbl;
        const char *str;
        /* TODO those are unused now */
        AVRational q;
    } default_val;
    double min;                 ///< minimum valid value for the option
    double max;                 ///< maximum valid value for the option

    int flags;
#define AV_OPT_FLAG_ENCODING_PARAM  1   ///< a generic parameter which can be set by the user for muxing or encoding
#define AV_OPT_FLAG_DECODING_PARAM  2   ///< a generic parameter which can be set by the user for demuxing or decoding
#define AV_OPT_FLAG_AUDIO_PARAM     8
#define AV_OPT_FLAG_VIDEO_PARAM     16
#define AV_OPT_FLAG_SUBTITLE_PARAM  32
/**
 * The option is intended for exporting values to the caller.
 */
#define AV_OPT_FLAG_EXPORT          64
/**
 * The option may not be set through the AVOptions API, only read.
 * This flag only makes sense when AV_OPT_FLAG_EXPORT is also set.
 */
#define AV_OPT_FLAG_READONLY        128
#define AV_OPT_FLAG_BSF_PARAM       (1<<8) ///< a generic parameter which can be set by the user for bit stream filtering
#define AV_OPT_FLAG_FILTERING_PARAM (1<<16) ///< a generic parameter which can be set by the user for filtering
//FIXME think about enc-audio, ... style flags

    /**
     * The logical unit to which the option belongs. Non-constant
     * options and corresponding named constants share the same
     * unit. May be NULL.
     */
    const char *unit;
} AVOption;

下面简单解释一下AVOption的几个成员变量：

name：名称。
help：简短的帮助。
offset：选项相对结构体首部地址的偏移量（这个很重要）。
type：选项的类型。
default_val：选项的默认值。
min：选项的最小值。
max：选项的最大值。
flags：一些标记。
unit：该选项所属的逻辑单元，可以为空

其中，default_val是一个union类型的变量，可以根据选项数据类型的不同，取int，double，char*，AVRational（表示分数）几种类型。

type是一个AVOptionType类型的变量。AVOptionType是一个枚举类型，定义如下。

enum AVOptionType{
    AV_OPT_TYPE_FLAGS,
    AV_OPT_TYPE_INT,
    AV_OPT_TYPE_INT64,
    AV_OPT_TYPE_DOUBLE,
    AV_OPT_TYPE_FLOAT,
    AV_OPT_TYPE_STRING,
    AV_OPT_TYPE_RATIONAL,
    AV_OPT_TYPE_BINARY,  ///< offset must point to a pointer immediately followed by an int for the length
    AV_OPT_TYPE_DICT,
    AV_OPT_TYPE_UINT64,
    AV_OPT_TYPE_CONST,
    AV_OPT_TYPE_IMAGE_SIZE, ///< offset must point to two consecutive integers
    AV_OPT_TYPE_PIXEL_FMT,
    AV_OPT_TYPE_SAMPLE_FMT,
    AV_OPT_TYPE_VIDEO_RATE, ///< offset must point to AVRational
    AV_OPT_TYPE_DURATION,
    AV_OPT_TYPE_COLOR,
    AV_OPT_TYPE_CHANNEL_LAYOUT,
    AV_OPT_TYPE_BOOL,
};

2、AVClass数据结构及其定义

AVClass最主要的作用就是给结构体（例如AVFormatContext等）增加AVOption功能的支持。换句话说AVClass就是AVOption和目标结构体之间的“桥梁”。AVClass要求必须声明为目标结构体的第一个变量。

AVClass中有一个option数组用于存储目标结构体的所有的AVOption。举个例子，AVFormatContext结构体，AVClass和AVOption之间的关系如下图所示。
在这里插入图片描述

/**
 * Describe the class of an AVClass context structure. That is an
 * arbitrary struct of which the first field is a pointer to an
 * AVClass struct (e.g. AVCodecContext, AVFormatContext etc.).
 */
typedef struct AVClass {
    /**
     * The name of the class; usually it is the same name as the
     * context structure type to which the AVClass is associated.
     */
    const char* class_name;

    /**
     * A pointer to a function which returns the name of a context
     * instance ctx associated with the class.
     */
    const char* (*item_name)(void* ctx);

    /**
     * a pointer to the first option specified in the class if any or NULL
     *
     * @see av_set_default_options()
     */
    const struct AVOption *option;

    /**
     * LIBAVUTIL_VERSION with which this structure was created.
     * This is used to allow fields to be added without requiring major
     * version bumps everywhere.
     */

    int version;

    /**
     * Offset in the structure where log_level_offset is stored.
     * 0 means there is no such variable
     */
    int log_level_offset_offset;

    /**
     * Offset in the structure where a pointer to the parent context for
     * logging is stored. For example a decoder could pass its AVCodecContext
     * to eval as such a parent context, which an av_log() implementation
     * could then leverage to display the parent context.
     * The offset can be NULL.
     */
    int parent_log_context_offset;

    /**
     * Return next AVOptions-enabled child or NULL
     */
    void* (*child_next)(void *obj, void *prev);

    /**
     * Return an AVClass corresponding to the next potential
     * AVOptions-enabled child.
     *
     * The difference between child_next and this is that
     * child_next iterates over _already existing_ objects, while
     * child_class_next iterates over _all possible_ children.
     */
    const struct AVClass* (*child_class_next)(const struct AVClass *prev);

    /**
     * Category used for visualization (like color)
     * This is only set if the category is equal for all objects using this class.
     * available since version (51 << 16 | 56 << 8 | 100)
     */
    AVClassCategory category;

    /**
     * Callback to return the category.
     * available since version (51 << 16 | 59 << 8 | 100)
     */
    AVClassCategory (*get_category)(void* ctx);

    /**
     * Callback to return the supported/allowed ranges.
     * available since version (52.12)
     */
    int (*query_ranges)(struct AVOptionRanges **, void *obj, const char *key, int flags);
} AVClass;

下面简单解释一下AVClass的几个已经理解的成员变量：

class_name：AVClass名称。
item_name：函数，获取与AVClass相关联的结构体实例的名称。
option：AVOption类型的数组（最重要）。
version：完成该AVClass的时候的LIBAVUTIL_VERSION。
category：AVClass的类型，是一个类型为AVClassCategory的枚举型变量。

AVClassCategory的定义如下：

typedef enum {
    AV_CLASS_CATEGORY_NA = 0,
    AV_CLASS_CATEGORY_INPUT,
    AV_CLASS_CATEGORY_OUTPUT,
    AV_CLASS_CATEGORY_MUXER,
    AV_CLASS_CATEGORY_DEMUXER,
    AV_CLASS_CATEGORY_ENCODER,
    AV_CLASS_CATEGORY_DECODER,
    AV_CLASS_CATEGORY_FILTER,
    AV_CLASS_CATEGORY_BITSTREAM_FILTER,
    AV_CLASS_CATEGORY_SWSCALER,
    AV_CLASS_CATEGORY_SWRESAMPLER,
    AV_CLASS_CATEGORY_DEVICE_VIDEO_OUTPUT = 40,
    AV_CLASS_CATEGORY_DEVICE_VIDEO_INPUT,
    AV_CLASS_CATEGORY_DEVICE_AUDIO_OUTPUT,
    AV_CLASS_CATEGORY_DEVICE_AUDIO_INPUT,
    AV_CLASS_CATEGORY_DEVICE_OUTPUT,
    AV_CLASS_CATEGORY_DEVICE_INPUT,
    AV_CLASS_CATEGORY_NB  ///< not part of ABI/API
}AVClassCategory;

2.1 AVFormatContext 中的AVClass

AVFormatContext 中的AVClass定义位于libavformat\options.c中，是一个名称为av_format_context_class的静态结构体。如下所示。

static const AVClass av_format_context_class = {
    .class_name     = "AVFormatContext",
    .item_name      = format_to_name,
    .option         = avformat_options,
    .version        = LIBAVUTIL_VERSION_INT,
    .child_next     = format_child_next,
    .child_class_next = format_child_class_next,
    .category       = AV_CLASS_CATEGORY_MUXER,
    .get_category   = get_category,
};

从源代码可以看出以下几点
（1）class_name
该AVClass名称是“AVFormatContext”。
（2）item_name
item_name指向一个函数format_to_name()，该函数定义如下所示。

static const char* format_to_name(void* ptr)
{
    AVFormatContext* fc = (AVFormatContext*) ptr;
    if(fc->iformat) return fc->iformat->name;
    else if(fc->oformat) return fc->oformat->name;
    else return "NULL";
}

从函数的定义可以看出，如果AVFormatContext结构体中的AVInputFormat结构体不为空，则返回AVInputFormat的name，然后尝试返回AVOutputFormat的name，如果AVOutputFormat也为空，则返回“NULL”。

（3）option
option字段则指向一个元素个数很多的静态数组avformat_options。该数组单独定义于libavformat\options_table.h中。其中包含了AVFormatContext支持的所有的AVOption，如下所示。

static const AVOption avformat_options[] = {
{"avioflags", NULL, OFFSET(avio_flags), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, INT_MIN, INT_MAX, D|E, "avioflags"},
{"direct", "reduce buffering", 0, AV_OPT_TYPE_CONST, {.i64 = AVIO_FLAG_DIRECT }, INT_MIN, INT_MAX, D|E, "avioflags"},
{"probesize", "set probing size", OFFSET(probesize), AV_OPT_TYPE_INT64, {.i64 = 5000000 }, 32, INT64_MAX, D},
{"formatprobesize", "number of bytes to probe file format", OFFSET(format_probesize), AV_OPT_TYPE_INT, {.i64 = PROBE_BUF_MAX}, 0, INT_MAX-1, D},
{"packetsize", "set packet size", OFFSET(packet_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, E},
{"fflags", NULL, OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = AVFMT_FLAG_AUTO_BSF }, INT_MIN, INT_MAX, D|E, "fflags"},
{"flush_packets", "reduce the latency by flushing out packets immediately", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_FLUSH_PACKETS }, INT_MIN, INT_MAX, E, "fflags"},
{"ignidx", "ignore index", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_IGNIDX }, INT_MIN, INT_MAX, D, "fflags"},
{"genpts", "generate pts", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_GENPTS }, INT_MIN, INT_MAX, D, "fflags"},
{"nofillin", "do not fill in missing values that can be exactly calculated", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_NOFILLIN }, INT_MIN, INT_MAX, D, "fflags"},
{"noparse", "disable AVParsers, this needs nofillin too", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_NOPARSE }, INT_MIN, INT_MAX, D, "fflags"},
{"igndts", "ignore dts", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_IGNDTS }, INT_MIN, INT_MAX, D, "fflags"},
{"discardcorrupt", "discard corrupted frames", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_DISCARD_CORRUPT }, INT_MIN, INT_MAX, D, "fflags"},
{"sortdts", "try to interleave outputted packets by dts", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_SORT_DTS }, INT_MIN, INT_MAX, D, "fflags"},
#if FF_API_LAVF_KEEPSIDE_FLAG
{"keepside", "deprecated, does nothing", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_KEEP_SIDE_DATA }, INT_MIN, INT_MAX, D, "fflags"},
#endif
{"fastseek", "fast but inaccurate seeks", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_FAST_SEEK }, INT_MIN, INT_MAX, D, "fflags"},
{"latm", "enable RTP MP4A-LATM payload", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_MP4A_LATM }, INT_MIN, INT_MAX, E, "fflags"},
{"nobuffer", "reduce the latency introduced by optional buffering", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_NOBUFFER }, 0, INT_MAX, D, "fflags"},
{"bitexact", "do not write random/volatile data", 0, AV_OPT_TYPE_CONST, { .i64 = AVFMT_FLAG_BITEXACT }, 0, 0, E, "fflags" },
{"shortest", "stop muxing with the shortest stream", 0, AV_OPT_TYPE_CONST, { .i64 = AVFMT_FLAG_SHORTEST }, 0, 0, E, "fflags" },
{"autobsf", "add needed bsfs automatically", 0, AV_OPT_TYPE_CONST, { .i64 = AVFMT_FLAG_AUTO_BSF }, 0, 0, E, "fflags" },
{"seek2any", "allow seeking to non-keyframes on demuxer level when supported", OFFSET(seek2any), AV_OPT_TYPE_BOOL, {.i64 = 0 }, 0, 1, D},
{"analyzeduration", "specify how many microseconds are analyzed to probe the input", OFFSET(max_analyze_duration), AV_OPT_TYPE_INT64, {.i64 = 0 }, 0, INT64_MAX, D},
{"cryptokey", "decryption key", OFFSET(key), AV_OPT_TYPE_BINARY, {.dbl = 0}, 0, 0, D},
{"indexmem", "max memory used for timestamp index (per stream)", OFFSET(max_index_size), AV_OPT_TYPE_INT, {.i64 = 1<<20 }, 0, INT_MAX, D},
{"rtbufsize", "max memory used for buffering real-time frames", OFFSET(max_picture_buffer), AV_OPT_TYPE_INT, {.i64 = 3041280 }, 0, INT_MAX, D}, /* defaults to 1s of 15fps 352x288 YUYV422 video */
{"fdebug", "print specific debug info", OFFSET(debug), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, 0, INT_MAX, E|D, "fdebug"},
{"ts", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_FDEBUG_TS }, INT_MIN, INT_MAX, E|D, "fdebug"},
{"max_delay", "maximum muxing or demuxing delay in microseconds", OFFSET(max_delay), AV_OPT_TYPE_INT, {.i64 = -1 }, -1, INT_MAX, E|D},
{"start_time_realtime", "wall-clock time when stream begins (PTS==0)", OFFSET(start_time_realtime), AV_OPT_TYPE_INT64, {.i64 = AV_NOPTS_VALUE}, INT64_MIN, INT64_MAX, E},
{"fpsprobesize", "number of frames used to probe fps", OFFSET(fps_probe_size), AV_OPT_TYPE_INT, {.i64 = -1}, -1, INT_MAX-1, D},
{"audio_preload", "microseconds by which audio packets should be interleaved earlier", OFFSET(audio_preload), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, E},
{"chunk_duration", "microseconds for each chunk", OFFSET(max_chunk_duration), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, E},
{"chunk_size", "size in bytes for each chunk", OFFSET(max_chunk_size), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, E},
/* this is a crutch for avconv, since it cannot deal with identically named options in different contexts.
 * to be removed when avconv is fixed */
{"f_err_detect", "set error detection flags (deprecated; use err_detect, save via avconv)", OFFSET(error_recognition), AV_OPT_TYPE_FLAGS, {.i64 = AV_EF_CRCCHECK }, INT_MIN, INT_MAX, D, "err_detect"},
{"err_detect", "set error detection flags", OFFSET(error_recognition), AV_OPT_TYPE_FLAGS, {.i64 = AV_EF_CRCCHECK }, INT_MIN, INT_MAX, D, "err_detect"},
{"crccheck", "verify embedded CRCs", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_CRCCHECK }, INT_MIN, INT_MAX, D, "err_detect"},
{"bitstream", "detect bitstream specification deviations", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_BITSTREAM }, INT_MIN, INT_MAX, D, "err_detect"},
{"buffer", "detect improper bitstream length", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_BUFFER }, INT_MIN, INT_MAX, D, "err_detect"},
{"explode", "abort decoding on minor error detection", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_EXPLODE }, INT_MIN, INT_MAX, D, "err_detect"},
{"ignore_err", "ignore errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_IGNORE_ERR }, INT_MIN, INT_MAX, D, "err_detect"},
{"careful",    "consider things that violate the spec, are fast to check and have not been seen in the wild as errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_CAREFUL }, INT_MIN, INT_MAX, D, "err_detect"},
{"compliant",  "consider all spec non compliancies as errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_COMPLIANT }, INT_MIN, INT_MAX, D, "err_detect"},
{"aggressive", "consider things that a sane encoder shouldn't do as an error", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_AGGRESSIVE }, INT_MIN, INT_MAX, D, "err_detect"},
{"use_wallclock_as_timestamps", "use wallclock as timestamps", OFFSET(use_wallclock_as_timestamps), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, D},
{"skip_initial_bytes", "set number of bytes to skip before reading header and frames", OFFSET(skip_initial_bytes), AV_OPT_TYPE_INT64, {.i64 = 0}, 0, INT64_MAX-1, D},
{"correct_ts_overflow", "correct single timestamp overflows", OFFSET(correct_ts_overflow), AV_OPT_TYPE_BOOL, {.i64 = 1}, 0, 1, D},
{"flush_packets", "enable flushing of the I/O context after each packet", OFFSET(flush_packets), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 1, E},
{"metadata_header_padding", "set number of bytes to be written as padding in a metadata header", OFFSET(metadata_header_padding), AV_OPT_TYPE_INT, {.i64 = -1}, -1, INT_MAX, E},
{"output_ts_offset", "set output timestamp offset", OFFSET(output_ts_offset), AV_OPT_TYPE_DURATION, {.i64 = 0}, -INT64_MAX, INT64_MAX, E},
{"max_interleave_delta", "maximum buffering duration for interleaving", OFFSET(max_interleave_delta), AV_OPT_TYPE_INT64, { .i64 = 10000000 }, 0, INT64_MAX, E },
{"f_strict", "how strictly to follow the standards (deprecated; use strict, save via avconv)", OFFSET(strict_std_compliance), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, D|E, "strict"},
{"strict", "how strictly to follow the standards", OFFSET(strict_std_compliance), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, D|E, "strict"},
{"very", "strictly conform to a older more strict version of the spec or reference software", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_VERY_STRICT }, INT_MIN, INT_MAX, D|E, "strict"},
{"strict", "strictly conform to all the things in the spec no matter what the consequences", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_STRICT }, INT_MIN, INT_MAX, D|E, "strict"},
{"normal", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_NORMAL }, INT_MIN, INT_MAX, D|E, "strict"},
{"unofficial", "allow unofficial extensions", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_UNOFFICIAL }, INT_MIN, INT_MAX, D|E, "strict"},
{"experimental", "allow non-standardized experimental variants", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_EXPERIMENTAL }, INT_MIN, INT_MAX, D|E, "strict"},
{"max_ts_probe", "maximum number of packets to read while waiting for the first timestamp", OFFSET(max_ts_probe), AV_OPT_TYPE_INT, { .i64 = 50 }, 0, INT_MAX, D },
{"avoid_negative_ts", "shift timestamps so they start at 0", OFFSET(avoid_negative_ts), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 2, E, "avoid_negative_ts"},
{"auto",              "enabled when required by target format",    0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_AVOID_NEG_TS_AUTO },              INT_MIN, INT_MAX, E, "avoid_negative_ts"},
{"disabled",          "do not change timestamps",                  0, AV_OPT_TYPE_CONST, {.i64 = 0 },                                    INT_MIN, INT_MAX, E, "avoid_negative_ts"},
{"make_non_negative", "shift timestamps so they are non negative", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_AVOID_NEG_TS_MAKE_NON_NEGATIVE }, INT_MIN, INT_MAX, E, "avoid_negative_ts"},
{"make_zero",         "shift timestamps so they start at 0",       0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_AVOID_NEG_TS_MAKE_ZERO },         INT_MIN, INT_MAX, E, "avoid_negative_ts"},
{"dump_separator", "set information dump field separator", OFFSET(dump_separator), AV_OPT_TYPE_STRING, {.str = ", "}, CHAR_MIN, CHAR_MAX, D|E},
{"codec_whitelist", "List of decoders that are allowed to be used", OFFSET(codec_whitelist), AV_OPT_TYPE_STRING, { .str = NULL },  CHAR_MIN, CHAR_MAX, D },
{"format_whitelist", "List of demuxers that are allowed to be used", OFFSET(format_whitelist), AV_OPT_TYPE_STRING, { .str = NULL },  CHAR_MIN, CHAR_MAX, D },
{"protocol_whitelist", "List of protocols that are allowed to be used", OFFSET(protocol_whitelist), AV_OPT_TYPE_STRING, { .str = NULL },  CHAR_MIN, CHAR_MAX, D },
{"protocol_blacklist", "List of protocols that are not allowed to be used", OFFSET(protocol_blacklist), AV_OPT_TYPE_STRING, { .str = NULL },  CHAR_MIN, CHAR_MAX, D },
{"max_streams", "maximum number of streams", OFFSET(max_streams), AV_OPT_TYPE_INT, { .i64 = 1000 }, 0, INT_MAX, D },
{NULL},
};

2.2AVFormatContext 中的AVClass

AVFormatContext 中的AVClass定义位于libavcodec\options.c中，是一个名称为av_codec_context_class的静态结构体。如下所示。

static const AVClass av_codec_context_class = {
    .class_name              = "AVCodecContext",
    .item_name               = context_to_name,
    .option                  = avcodec_options,
    .version                 = LIBAVUTIL_VERSION_INT,
    .log_level_offset_offset = offsetof(AVCodecContext, log_level_offset),
    .child_next              = codec_child_next,
    .child_class_next        = codec_child_class_next,
    .category                = AV_CLASS_CATEGORY_ENCODER,
    .get_category            = get_category,
};

从源代码可以看出：
（1）class_name
该AVClass名称是“AVCodecContext”。
（2）item_name
item_name指向一个函数context_to_name ()，该函数定义如下所示

static const char* context_to_name(void* ptr) {
    AVCodecContext *avc= ptr;

    if(avc && avc->codec && avc->codec->name)
        return avc->codec->name;
    else
        return "NULL";
}

从函数的定义可以看出，如果AVCodecContext中的Codec结构体不为空，则返回Codec的name，否则返回“NULL”。
（3）category
option字段则指向一个元素个数极多的静态数组avcodec_options。该数组单独定义于libavcodec\options_table.h中。其中包含了AVCodecContext支持的所有的AVOption。由于该数组定义实在是太多了，在这里仅贴出它前面的一小部分。

static const AVOption avcodec_options[] = {
{"b", "set bitrate (in bits/s)", OFFSET(bit_rate), AV_OPT_TYPE_INT64, {.i64 = AV_CODEC_DEFAULT_BITRATE }, 0, INT64_MAX, A|V|E},
{"ab", "set bitrate (in bits/s)", OFFSET(bit_rate), AV_OPT_TYPE_INT64, {.i64 = 128*1000 }, 0, INT_MAX, A|E},
{"bt", "Set video bitrate tolerance (in bits/s). In 1-pass mode, bitrate tolerance specifies how far "
       "ratecontrol is willing to deviate from the target average bitrate value. This is not related "
       "to minimum/maximum bitrate. Lowering tolerance too much has an adverse effect on quality.",
       OFFSET(bit_rate_tolerance), AV_OPT_TYPE_INT, {.i64 = AV_CODEC_DEFAULT_BITRATE*20 }, 1, INT_MAX, V|E},
{"flags", NULL, OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, 0, UINT_MAX, V|A|S|E|D, "flags"},
{"unaligned", "allow decoders to produce unaligned output", 0, AV_OPT_TYPE_CONST, { .i64 = AV_CODEC_FLAG_UNALIGNED }, INT_MIN, INT_MAX, V | D, "flags" },
{"mv4", "use four motion vectors per macroblock (MPEG-4)", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_4MV }, INT_MIN, INT_MAX, V|E, "flags"},
{"qpel", "use 1/4-pel motion compensation", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_QPEL }, INT_MIN, INT_MAX, V|E, "flags"},
{"loop", "use loop filter", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_LOOP_FILTER }, INT_MIN, INT_MAX, V|E, "flags"},
{"qscale", "use fixed qscale", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_QSCALE }, INT_MIN, INT_MAX, 0, "flags"},
{"pass1", "use internal 2-pass ratecontrol in first  pass mode", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_PASS1 }, INT_MIN, INT_MAX, 0, "flags"},
{"pass2", "use internal 2-pass ratecontrol in second pass mode", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_PASS2 }, INT_MIN, INT_MAX, 0, "flags"},
{"gray", "only decode/encode grayscale", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_GRAY }, INT_MIN, INT_MAX, V|E|D, "flags"},
{"psnr", "error[?] variables will be set during encoding", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_PSNR }, INT_MIN, INT_MAX, V|E, "flags"},
{"truncated", "Input bitstream might be randomly truncated", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_TRUNCATED }, INT_MIN, INT_MAX, V|D, "flags"},
{"ildct", "use interlaced DCT", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_INTERLACED_DCT }, INT_MIN, INT_MAX, V|E, "flags"},
{"low_delay", "force low delay", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_LOW_DELAY }, INT_MIN, INT_MAX, V|D|E, "flags"},
{"global_header", "place global headers in extradata instead of every keyframe", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_GLOBAL_HEADER }, INT_MIN, INT_MAX, V|A|E, "flags"},
{"bitexact", "use only bitexact functions (except (I)DCT)", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_BITEXACT }, INT_MIN, INT_MAX, A|V|S|D|E, "flags"},
{"aic", "H.263 advanced intra coding / MPEG-4 AC prediction", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_AC_PRED }, INT_MIN, INT_MAX, V|E, "flags"},
{"ilme", "interlaced motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_INTERLACED_ME }, INT_MIN, INT_MAX, V|E, "flags"},
{"cgop", "closed GOP", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_CLOSED_GOP }, INT_MIN, INT_MAX, V|E, "flags"},
{"output_corrupt", "Output even potentially corrupted frames", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_OUTPUT_CORRUPT }, INT_MIN, INT_MAX, V|D, "flags"},
{"fast", "allow non-spec-compliant speedup tricks", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_FAST }, INT_MIN, INT_MAX, V|E, "flags2"},
{"noout", "skip bitstream encoding", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_NO_OUTPUT }, INT_MIN, INT_MAX, V|E, "flags2"},
{"ignorecrop", "ignore cropping information from sps", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_IGNORE_CROP }, INT_MIN, INT_MAX, V|D, "flags2"},
{"local_header", "place global headers at every keyframe instead of in extradata", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_LOCAL_HEADER }, INT_MIN, INT_MAX, V|E, "flags2"},
{"chunks", "Frame data might be split into multiple chunks", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_CHUNKS }, INT_MIN, INT_MAX, V|D, "flags2"},
{"showall", "Show all frames before the first keyframe", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_SHOW_ALL }, INT_MIN, INT_MAX, V|D, "flags2"},
{"export_mvs", "export motion vectors through frame side data", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_EXPORT_MVS}, INT_MIN, INT_MAX, V|D, "flags2"},
{"skip_manual", "do not skip samples and export skip information as frame side data", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_SKIP_MANUAL}, INT_MIN, INT_MAX, V|D, "flags2"},
{"ass_ro_flush_noop", "do not reset ASS ReadOrder field on flush", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG2_RO_FLUSH_NOOP}, INT_MIN, INT_MAX, S|D, "flags2"},
{"time_base", NULL, OFFSET(time_base), AV_OPT_TYPE_RATIONAL, {.dbl = 0}, 0, INT_MAX},
{"g", "set the group of picture (GOP) size", OFFSET(gop_size), AV_OPT_TYPE_INT, {.i64 = 12 }, INT_MIN, INT_MAX, V|E},
{"ar", "set audio sampling rate (in Hz)", OFFSET(sample_rate), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, A|D|E},
{"ac", "set number of audio channels", OFFSET(channels), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, A|D|E},
{"cutoff", "set cutoff bandwidth", OFFSET(cutoff), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, A|E},
{"frame_size", NULL, OFFSET(frame_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, A|E},
{"frame_number", NULL, OFFSET(frame_number), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"delay", NULL, OFFSET(delay), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"qcomp", "video quantizer scale compression (VBR). Constant of ratecontrol equation. "
          "Recommended range for default rc_eq: 0.0-1.0",
          OFFSET(qcompress), AV_OPT_TYPE_FLOAT, {.dbl = 0.5 }, -FLT_MAX, FLT_MAX, V|E},
{"qblur", "video quantizer scale blur (VBR)", OFFSET(qblur), AV_OPT_TYPE_FLOAT, {.dbl = 0.5 }, -1, FLT_MAX, V|E},
{"qmin", "minimum video quantizer scale (VBR)", OFFSET(qmin), AV_OPT_TYPE_INT, {.i64 = 2 }, -1, 69, V|E},
{"qmax", "maximum video quantizer scale (VBR)", OFFSET(qmax), AV_OPT_TYPE_INT, {.i64 = 31 }, -1, 1024, V|E},
{"qdiff", "maximum difference between the quantizer scales (VBR)", OFFSET(max_qdiff), AV_OPT_TYPE_INT, {.i64 = 3 }, INT_MIN, INT_MAX, V|E},
{"bf", "set maximum number of B-frames between non-B-frames", OFFSET(max_b_frames), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, -1, INT_MAX, V|E},
{"b_qfactor", "QP factor between P- and B-frames", OFFSET(b_quant_factor), AV_OPT_TYPE_FLOAT, {.dbl = 1.25 }, -FLT_MAX, FLT_MAX, V|E},
#if FF_API_PRIVATE_OPT
{"b_strategy", "strategy to choose between I/P/B-frames", OFFSET(b_frame_strategy), AV_OPT_TYPE_INT, {.i64 = 0 }, INT_MIN, INT_MAX, V|E},
{"ps", "RTP payload size in bytes", OFFSET(rtp_payload_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
#endif
#if FF_API_STAT_BITS
{"mv_bits", NULL, OFFSET(mv_bits), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"header_bits", NULL, OFFSET(header_bits), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"i_tex_bits", NULL, OFFSET(i_tex_bits), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"p_tex_bits", NULL, OFFSET(p_tex_bits), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"i_count", NULL, OFFSET(i_count), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"p_count", NULL, OFFSET(p_count), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"skip_count", NULL, OFFSET(skip_count), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"misc_bits", NULL, OFFSET(misc_bits), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"frame_bits", NULL, OFFSET(frame_bits), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
#endif
{"codec_tag", NULL, OFFSET(codec_tag), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"bug", "work around not autodetected encoder bugs", OFFSET(workaround_bugs), AV_OPT_TYPE_FLAGS, {.i64 = FF_BUG_AUTODETECT }, INT_MIN, INT_MAX, V|D, "bug"},
{"autodetect", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_AUTODETECT }, INT_MIN, INT_MAX, V|D, "bug"},
{"xvid_ilace", "Xvid interlacing bug (autodetected if FOURCC == XVIX)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_XVID_ILACE }, INT_MIN, INT_MAX, V|D, "bug"},
{"ump4", "(autodetected if FOURCC == UMP4)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_UMP4 }, INT_MIN, INT_MAX, V|D, "bug"},
{"no_padding", "padding bug (autodetected)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_NO_PADDING }, INT_MIN, INT_MAX, V|D, "bug"},
{"amv", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_AMV }, INT_MIN, INT_MAX, V|D, "bug"},
{"qpel_chroma", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_QPEL_CHROMA }, INT_MIN, INT_MAX, V|D, "bug"},
{"std_qpel", "old standard qpel (autodetected per FOURCC/version)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_STD_QPEL }, INT_MIN, INT_MAX, V|D, "bug"},
{"qpel_chroma2", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_QPEL_CHROMA2 }, INT_MIN, INT_MAX, V|D, "bug"},
{"direct_blocksize", "direct-qpel-blocksize bug (autodetected per FOURCC/version)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_DIRECT_BLOCKSIZE }, INT_MIN, INT_MAX, V|D, "bug"},
{"edge", "edge padding bug (autodetected per FOURCC/version)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_EDGE }, INT_MIN, INT_MAX, V|D, "bug"},
{"hpel_chroma", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_HPEL_CHROMA }, INT_MIN, INT_MAX, V|D, "bug"},
{"dc_clip", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_DC_CLIP }, INT_MIN, INT_MAX, V|D, "bug"},
{"ms", "work around various bugs in Microsoft's broken decoders", 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_MS }, INT_MIN, INT_MAX, V|D, "bug"},
{"trunc", "truncated frames", 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_TRUNCATED}, INT_MIN, INT_MAX, V|D, "bug"},
{"iedge", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_BUG_IEDGE }, INT_MIN, INT_MAX, V|D, "bug"},
{"strict", "how strictly to follow the standards", OFFSET(strict_std_compliance), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, A|V|D|E, "strict"},
{"very", "strictly conform to a older more strict version of the spec or reference software", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_VERY_STRICT }, INT_MIN, INT_MAX, A|V|D|E, "strict"},
{"strict", "strictly conform to all the things in the spec no matter what the consequences", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_STRICT }, INT_MIN, INT_MAX, A|V|D|E, "strict"},
{"normal", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_NORMAL }, INT_MIN, INT_MAX, A|V|D|E, "strict"},
{"unofficial", "allow unofficial extensions", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_UNOFFICIAL }, INT_MIN, INT_MAX, A|V|D|E, "strict"},
{"experimental", "allow non-standardized experimental things", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_EXPERIMENTAL }, INT_MIN, INT_MAX, A|V|D|E, "strict"},
{"b_qoffset", "QP offset between P- and B-frames", OFFSET(b_quant_offset), AV_OPT_TYPE_FLOAT, {.dbl = 1.25 }, -FLT_MAX, FLT_MAX, V|E},
{"err_detect", "set error detection flags", OFFSET(err_recognition), AV_OPT_TYPE_FLAGS, {.i64 = 0 }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"crccheck", "verify embedded CRCs", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_CRCCHECK }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"bitstream", "detect bitstream specification deviations", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_BITSTREAM }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"buffer", "detect improper bitstream length", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_BUFFER }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"explode", "abort decoding on minor error detection", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_EXPLODE }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"ignore_err", "ignore errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_IGNORE_ERR }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"careful",    "consider things that violate the spec, are fast to check and have not been seen in the wild as errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_CAREFUL }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"compliant",  "consider all spec non compliancies as errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_COMPLIANT }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"aggressive", "consider things that a sane encoder should not do as an error", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_AGGRESSIVE }, INT_MIN, INT_MAX, A|V|D, "err_detect"},
{"has_b_frames", NULL, OFFSET(has_b_frames), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX},
{"block_align", NULL, OFFSET(block_align), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX},
#if FF_API_PRIVATE_OPT
{"mpeg_quant", "use MPEG quantizers instead of H.263", OFFSET(mpeg_quant), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
#endif
{"rc_override_count", NULL, OFFSET(rc_override_count), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"maxrate", "maximum bitrate (in bits/s). Used for VBV together with bufsize.", OFFSET(rc_max_rate), AV_OPT_TYPE_INT64, {.i64 = DEFAULT }, 0, INT_MAX, V|A|E},
{"minrate", "minimum bitrate (in bits/s). Most useful in setting up a CBR encode. It is of little use otherwise.",
            OFFSET(rc_min_rate), AV_OPT_TYPE_INT64, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|A|E},
{"bufsize", "set ratecontrol buffer size (in bits)", OFFSET(rc_buffer_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, A|V|E},
{"i_qfactor", "QP factor between P- and I-frames", OFFSET(i_quant_factor), AV_OPT_TYPE_FLOAT, {.dbl = -0.8 }, -FLT_MAX, FLT_MAX, V|E},
{"i_qoffset", "QP offset between P- and I-frames", OFFSET(i_quant_offset), AV_OPT_TYPE_FLOAT, {.dbl = 0.0 }, -FLT_MAX, FLT_MAX, V|E},
{"dct", "DCT algorithm", OFFSET(dct_algo), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, V|E, "dct"},
{"auto", "autoselect a good one", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DCT_AUTO }, INT_MIN, INT_MAX, V|E, "dct"},
{"fastint", "fast integer", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DCT_FASTINT }, INT_MIN, INT_MAX, V|E, "dct"},
{"int", "accurate integer", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DCT_INT }, INT_MIN, INT_MAX, V|E, "dct"},
{"mmx", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_DCT_MMX }, INT_MIN, INT_MAX, V|E, "dct"},
{"altivec", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_DCT_ALTIVEC }, INT_MIN, INT_MAX, V|E, "dct"},
{"faan", "floating point AAN DCT", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DCT_FAAN }, INT_MIN, INT_MAX, V|E, "dct"},
{"lumi_mask", "compresses bright areas stronger than medium ones", OFFSET(lumi_masking), AV_OPT_TYPE_FLOAT, {.dbl = 0 }, -FLT_MAX, FLT_MAX, V|E},
{"tcplx_mask", "temporal complexity masking", OFFSET(temporal_cplx_masking), AV_OPT_TYPE_FLOAT, {.dbl = 0 }, -FLT_MAX, FLT_MAX, V|E},
{"scplx_mask", "spatial complexity masking", OFFSET(spatial_cplx_masking), AV_OPT_TYPE_FLOAT, {.dbl = 0 }, -FLT_MAX, FLT_MAX, V|E},
{"p_mask", "inter masking", OFFSET(p_masking), AV_OPT_TYPE_FLOAT, {.dbl = 0 }, -FLT_MAX, FLT_MAX, V|E},
{"dark_mask", "compresses dark areas stronger than medium ones", OFFSET(dark_masking), AV_OPT_TYPE_FLOAT, {.dbl = 0 }, -FLT_MAX, FLT_MAX, V|E},
{"idct", "select IDCT implementation", OFFSET(idct_algo), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, V|E|D, "idct"},
{"auto", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_AUTO }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"int", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_INT }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"simple", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_SIMPLE }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"simplemmx", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_SIMPLEMMX }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"arm", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_ARM }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"altivec", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_ALTIVEC }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"simplearm", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_SIMPLEARM }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"simplearmv5te", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_SIMPLEARMV5TE }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"simplearmv6", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_SIMPLEARMV6 }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"simpleneon", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_SIMPLENEON }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"xvid", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_XVID }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"xvidmmx", "deprecated, for compatibility only", 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_XVID }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"faani", "floating point AAN IDCT", 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_FAAN }, INT_MIN, INT_MAX, V|D|E, "idct"},
{"simpleauto", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_IDCT_SIMPLEAUTO }, INT_MIN, INT_MAX, V|E|D, "idct"},
{"slice_count", NULL, OFFSET(slice_count), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"ec", "set error concealment strategy", OFFSET(error_concealment), AV_OPT_TYPE_FLAGS, {.i64 = 3 }, INT_MIN, INT_MAX, V|D, "ec"},
{"guess_mvs", "iterative motion vector (MV) search (slow)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_EC_GUESS_MVS }, INT_MIN, INT_MAX, V|D, "ec"},
{"deblock", "use strong deblock filter for damaged MBs", 0, AV_OPT_TYPE_CONST, {.i64 = FF_EC_DEBLOCK }, INT_MIN, INT_MAX, V|D, "ec"},
{"favor_inter", "favor predicting from the previous frame", 0, AV_OPT_TYPE_CONST, {.i64 = FF_EC_FAVOR_INTER }, INT_MIN, INT_MAX, V|D, "ec"},
{"bits_per_coded_sample", NULL, OFFSET(bits_per_coded_sample), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX},
#if FF_API_PRIVATE_OPT
{"pred", "prediction method", OFFSET(prediction_method), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E, "pred"},
{"left", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PRED_LEFT }, INT_MIN, INT_MAX, V|E, "pred"},
{"plane", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PRED_PLANE }, INT_MIN, INT_MAX, V|E, "pred"},
{"median", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PRED_MEDIAN }, INT_MIN, INT_MAX, V|E, "pred"},
#endif
{"aspect", "sample aspect ratio", OFFSET(sample_aspect_ratio), AV_OPT_TYPE_RATIONAL, {.dbl = 0}, 0, 10, V|E},
{"sar",    "sample aspect ratio", OFFSET(sample_aspect_ratio), AV_OPT_TYPE_RATIONAL, {.dbl = 0}, 0, 10, V|E},
{"debug", "print specific debug info", OFFSET(debug), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, 0, INT_MAX, V|A|S|E|D, "debug"},
{"pict", "picture info", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_PICT_INFO }, INT_MIN, INT_MAX, V|D, "debug"},
{"rc", "rate control", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_RC }, INT_MIN, INT_MAX, V|E, "debug"},
{"bitstream", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_BITSTREAM }, INT_MIN, INT_MAX, V|D, "debug"},
{"mb_type", "macroblock (MB) type", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_MB_TYPE }, INT_MIN, INT_MAX, V|D, "debug"},
{"qp", "per-block quantization parameter (QP)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_QP }, INT_MIN, INT_MAX, V|D, "debug"},
#if FF_API_DEBUG_MV
{"mv", "motion vector", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_MV }, INT_MIN, INT_MAX, V|D, "debug"},
#endif
{"dct_coeff", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_DCT_COEFF }, INT_MIN, INT_MAX, V|D, "debug"},
{"green_metadata", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_GREEN_MD }, INT_MIN, INT_MAX, V|D, "debug"},
{"skip", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_SKIP }, INT_MIN, INT_MAX, V|D, "debug"},
{"startcode", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_STARTCODE }, INT_MIN, INT_MAX, V|D, "debug"},
{"er", "error recognition", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_ER }, INT_MIN, INT_MAX, V|D, "debug"},
{"mmco", "memory management control operations (H.264)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_MMCO }, INT_MIN, INT_MAX, V|D, "debug"},
{"bugs", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_BUGS }, INT_MIN, INT_MAX, V|D, "debug"},
#if FF_API_DEBUG_MV
{"vis_qp", "visualize quantization parameter (QP), lower QP are tinted greener", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_VIS_QP }, INT_MIN, INT_MAX, V|D, "debug"},
{"vis_mb_type", "visualize block types", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_VIS_MB_TYPE }, INT_MIN, INT_MAX, V|D, "debug"},
#endif
{"buffers", "picture buffer allocations", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_BUFFERS }, INT_MIN, INT_MAX, V|D, "debug"},
{"thread_ops", "threading operations", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_THREADS }, INT_MIN, INT_MAX, V|A|D, "debug"},
{"nomc", "skip motion compensation", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_NOMC }, INT_MIN, INT_MAX, V|A|D, "debug"},
{"cmp", "full-pel ME compare function", OFFSET(me_cmp), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"subcmp", "sub-pel ME compare function", OFFSET(me_sub_cmp), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"mbcmp", "macroblock compare function", OFFSET(mb_cmp), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"ildctcmp", "interlaced DCT compare function", OFFSET(ildct_cmp), AV_OPT_TYPE_INT, {.i64 = FF_CMP_VSAD }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"dia_size", "diamond type & size for motion estimation", OFFSET(dia_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
{"last_pred", "amount of motion predictors from the previous frame", OFFSET(last_predictor_count), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
#if FF_API_PRIVATE_OPT
{"preme", "pre motion estimation", OFFSET(pre_me), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
#endif
{"precmp", "pre motion estimation compare function", OFFSET(me_pre_cmp), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"sad", "sum of absolute differences, fast", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_SAD }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"sse", "sum of squared errors", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_SSE }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"satd", "sum of absolute Hadamard transformed differences", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_SATD }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"dct", "sum of absolute DCT transformed differences", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_DCT }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"psnr", "sum of squared quantization errors (avoid, low quality)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_PSNR }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"bit", "number of bits needed for the block", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_BIT }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"rd", "rate distortion optimal, slow", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_RD }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"zero", "0", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_ZERO }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"vsad", "sum of absolute vertical differences", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_VSAD }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"vsse", "sum of squared vertical differences", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_VSSE }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"nsse", "noise preserving sum of squared differences", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_NSSE }, INT_MIN, INT_MAX, V|E, "cmp_func"},
#if CONFIG_SNOW_ENCODER
{"w53", "5/3 wavelet, only used in snow", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_W53 }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"w97", "9/7 wavelet, only used in snow", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_W97 }, INT_MIN, INT_MAX, V|E, "cmp_func"},
#endif
{"dctmax", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_DCTMAX }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"chroma", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_CHROMA }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"msad", "sum of absolute differences, median predicted", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CMP_MEDIAN_SAD }, INT_MIN, INT_MAX, V|E, "cmp_func"},
{"pre_dia_size", "diamond type & size for motion estimation pre-pass", OFFSET(pre_dia_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
{"subq", "sub-pel motion estimation quality", OFFSET(me_subpel_quality), AV_OPT_TYPE_INT, {.i64 = 8 }, INT_MIN, INT_MAX, V|E},
{"me_range", "limit motion vectors range (1023 for DivX player)", OFFSET(me_range), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
{"global_quality", NULL, OFFSET(global_quality), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|A|E},
#if FF_API_CODER_TYPE
{"coder", NULL, OFFSET(coder_type), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E, "coder"},
{"vlc", "variable length coder / Huffman coder", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CODER_TYPE_VLC }, INT_MIN, INT_MAX, V|E, "coder"},
{"ac", "arithmetic coder", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CODER_TYPE_AC }, INT_MIN, INT_MAX, V|E, "coder"},
{"raw", "raw (no encoding)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CODER_TYPE_RAW }, INT_MIN, INT_MAX, V|E, "coder"},
{"rle", "run-length coder", 0, AV_OPT_TYPE_CONST, {.i64 = FF_CODER_TYPE_RLE }, INT_MIN, INT_MAX, V|E, "coder"},
#endif /* FF_API_CODER_TYPE */
#if FF_API_PRIVATE_OPT
{"context", "context model", OFFSET(context_model), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
#endif
{"slice_flags", NULL, OFFSET(slice_flags), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX},
{"mbd", "macroblock decision algorithm (high quality mode)", OFFSET(mb_decision), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, 2, V|E, "mbd"},
{"simple", "use mbcmp", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MB_DECISION_SIMPLE }, INT_MIN, INT_MAX, V|E, "mbd"},
{"bits", "use fewest bits", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MB_DECISION_BITS }, INT_MIN, INT_MAX, V|E, "mbd"},
{"rd", "use best rate distortion", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MB_DECISION_RD }, INT_MIN, INT_MAX, V|E, "mbd"},
#if FF_API_PRIVATE_OPT
{"sc_threshold", "scene change threshold", OFFSET(scenechange_threshold), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
#endif
#if FF_API_PRIVATE_OPT
{"nr", "noise reduction", OFFSET(noise_reduction), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
#endif
{"rc_init_occupancy", "number of bits which should be loaded into the rc buffer before decoding starts", OFFSET(rc_initial_buffer_occupancy), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
{"flags2", NULL, OFFSET(flags2), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT}, 0, UINT_MAX, V|A|E|D, "flags2"},
{"threads", "set the number of threads", OFFSET(thread_count), AV_OPT_TYPE_INT, {.i64 = 1 }, 0, INT_MAX, V|A|E|D, "threads"},
{"auto", "autodetect a suitable number of threads to use", 0, AV_OPT_TYPE_CONST, {.i64 = 0 }, INT_MIN, INT_MAX, V|E|D, "threads"},
{"dc", "intra_dc_precision", OFFSET(intra_dc_precision), AV_OPT_TYPE_INT, {.i64 = 0 }, -8, 16, V|E},
{"nssew", "nsse weight", OFFSET(nsse_weight), AV_OPT_TYPE_INT, {.i64 = 8 }, INT_MIN, INT_MAX, V|E},
{"skip_top", "number of macroblock rows at the top which are skipped", OFFSET(skip_top), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|D},
{"skip_bottom", "number of macroblock rows at the bottom which are skipped", OFFSET(skip_bottom), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|D},
{"profile", NULL, OFFSET(profile), AV_OPT_TYPE_INT, {.i64 = FF_PROFILE_UNKNOWN }, INT_MIN, INT_MAX, V|A|E, "profile"},
{"unknown", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_UNKNOWN }, INT_MIN, INT_MAX, V|A|E, "profile"},
{"aac_main", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_AAC_MAIN }, INT_MIN, INT_MAX, A|E, "profile"},
{"aac_low", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_AAC_LOW }, INT_MIN, INT_MAX, A|E, "profile"},
{"aac_ssr", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_AAC_SSR }, INT_MIN, INT_MAX, A|E, "profile"},
{"aac_ltp", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_AAC_LTP }, INT_MIN, INT_MAX, A|E, "profile"},
{"aac_he", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_AAC_HE }, INT_MIN, INT_MAX, A|E, "profile"},
{"aac_he_v2", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_AAC_HE_V2 }, INT_MIN, INT_MAX, A|E, "profile"},
{"aac_ld", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_AAC_LD }, INT_MIN, INT_MAX, A|E, "profile"},
{"aac_eld", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_AAC_ELD }, INT_MIN, INT_MAX, A|E, "profile"},
{"mpeg2_aac_low", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_MPEG2_AAC_LOW }, INT_MIN, INT_MAX, A|E, "profile"},
{"mpeg2_aac_he", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_MPEG2_AAC_HE }, INT_MIN, INT_MAX, A|E, "profile"},
{"dts", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_DTS }, INT_MIN, INT_MAX, A|E, "profile"},
{"dts_es", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_DTS_ES }, INT_MIN, INT_MAX, A|E, "profile"},
{"dts_96_24", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_DTS_96_24 }, INT_MIN, INT_MAX, A|E, "profile"},
{"dts_hd_hra", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_DTS_HD_HRA }, INT_MIN, INT_MAX, A|E, "profile"},
{"dts_hd_ma", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_DTS_HD_MA }, INT_MIN, INT_MAX, A|E, "profile"},
{"mpeg4_sp",   NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_MPEG4_SIMPLE }, INT_MIN, INT_MAX, V|E, "profile"},
{"mpeg4_core", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_MPEG4_CORE }, INT_MIN, INT_MAX, V|E, "profile"},
{"mpeg4_main", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_MPEG4_MAIN }, INT_MIN, INT_MAX, V|E, "profile"},
{"mpeg4_asp",  NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_MPEG4_ADVANCED_SIMPLE }, INT_MIN, INT_MAX, V|E, "profile"},
{"main10",  NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_HEVC_MAIN_10 }, INT_MIN, INT_MAX, V|E, "profile"},
{"msbc",  NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_PROFILE_SBC_MSBC }, INT_MIN, INT_MAX, A|E, "profile"},
{"level", NULL, OFFSET(level), AV_OPT_TYPE_INT, {.i64 = FF_LEVEL_UNKNOWN }, INT_MIN, INT_MAX, V|A|E, "level"},
{"unknown", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_LEVEL_UNKNOWN }, INT_MIN, INT_MAX, V|A|E, "level"},
{"lowres", "decode at 1= 1/2, 2=1/4, 3=1/8 resolutions", OFFSET(lowres), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, INT_MAX, V|A|D},
#if FF_API_PRIVATE_OPT
{"skip_threshold", "frame skip threshold", OFFSET(frame_skip_threshold), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
{"skip_factor", "frame skip factor", OFFSET(frame_skip_factor), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
{"skip_exp", "frame skip exponent", OFFSET(frame_skip_exp), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
{"skipcmp", "frame skip compare function", OFFSET(frame_skip_cmp), AV_OPT_TYPE_INT, {.i64 = FF_CMP_DCTMAX }, INT_MIN, INT_MAX, V|E, "cmp_func"},
#endif
{"mblmin", "minimum macroblock Lagrange factor (VBR)", OFFSET(mb_lmin), AV_OPT_TYPE_INT, {.i64 = FF_QP2LAMBDA * 2 }, 1, FF_LAMBDA_MAX, V|E},
{"mblmax", "maximum macroblock Lagrange factor (VBR)", OFFSET(mb_lmax), AV_OPT_TYPE_INT, {.i64 = FF_QP2LAMBDA * 31 }, 1, FF_LAMBDA_MAX, V|E},
#if FF_API_PRIVATE_OPT
{"mepc", "motion estimation bitrate penalty compensation (1.0 = 256)", OFFSET(me_penalty_compensation), AV_OPT_TYPE_INT, {.i64 = 256 }, INT_MIN, INT_MAX, V|E},
#endif
{"skip_loop_filter", "skip loop filtering process for the selected frames", OFFSET(skip_loop_filter), AV_OPT_TYPE_INT, {.i64 = AVDISCARD_DEFAULT }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"skip_idct"       , "skip IDCT/dequantization for the selected frames",    OFFSET(skip_idct),        AV_OPT_TYPE_INT, {.i64 = AVDISCARD_DEFAULT }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"skip_frame"      , "skip decoding for the selected frames",               OFFSET(skip_frame),       AV_OPT_TYPE_INT, {.i64 = AVDISCARD_DEFAULT }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"none"            , "discard no frame",                    0, AV_OPT_TYPE_CONST, {.i64 = AVDISCARD_NONE    }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"default"         , "discard useless frames",              0, AV_OPT_TYPE_CONST, {.i64 = AVDISCARD_DEFAULT }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"noref"           , "discard all non-reference frames",    0, AV_OPT_TYPE_CONST, {.i64 = AVDISCARD_NONREF  }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"bidir"           , "discard all bidirectional frames",    0, AV_OPT_TYPE_CONST, {.i64 = AVDISCARD_BIDIR   }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"nokey"           , "discard all frames except keyframes", 0, AV_OPT_TYPE_CONST, {.i64 = AVDISCARD_NONKEY  }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"nointra"         , "discard all frames except I frames",  0, AV_OPT_TYPE_CONST, {.i64 = AVDISCARD_NONINTRA}, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"all"             , "discard all frames",                  0, AV_OPT_TYPE_CONST, {.i64 = AVDISCARD_ALL     }, INT_MIN, INT_MAX, V|D, "avdiscard"},
{"bidir_refine", "refine the two motion vectors used in bidirectional macroblocks", OFFSET(bidir_refine), AV_OPT_TYPE_INT, {.i64 = 1 }, 0, 4, V|E},
#if FF_API_PRIVATE_OPT
{"brd_scale", "downscale frames for dynamic B-frame decision", OFFSET(brd_scale), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, 10, V|E},
#endif
{"keyint_min", "minimum interval between IDR-frames", OFFSET(keyint_min), AV_OPT_TYPE_INT, {.i64 = 25 }, INT_MIN, INT_MAX, V|E},
{"refs", "reference frames to consider for motion compensation", OFFSET(refs), AV_OPT_TYPE_INT, {.i64 = 1 }, INT_MIN, INT_MAX, V|E},
#if FF_API_PRIVATE_OPT
{"chromaoffset", "chroma QP offset from luma", OFFSET(chromaoffset), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|E},
#endif
{"trellis", "rate-distortion optimal quantization", OFFSET(trellis), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, V|A|E},
{"mv0_threshold", NULL, OFFSET(mv0_threshold), AV_OPT_TYPE_INT, {.i64 = 256 }, 0, INT_MAX, V|E},
#if FF_API_PRIVATE_OPT
{"b_sensitivity", "adjust sensitivity of b_frame_strategy 1", OFFSET(b_sensitivity), AV_OPT_TYPE_INT, {.i64 = 40 }, 1, INT_MAX, V|E},
#endif
{"compression_level", NULL, OFFSET(compression_level), AV_OPT_TYPE_INT, {.i64 = FF_COMPRESSION_DEFAULT }, INT_MIN, INT_MAX, V|A|E},
#if FF_API_PRIVATE_OPT
{"min_prediction_order", NULL, OFFSET(min_prediction_order), AV_OPT_TYPE_INT, {.i64 = -1 }, INT_MIN, INT_MAX, A|E},
{"max_prediction_order", NULL, OFFSET(max_prediction_order), AV_OPT_TYPE_INT, {.i64 = -1 }, INT_MIN, INT_MAX, A|E},
{"timecode_frame_start", "GOP timecode frame start number, in non-drop-frame format", OFFSET(timecode_frame_start), AV_OPT_TYPE_INT64, {.i64 = -1 }, -1, INT64_MAX, V|E},
#endif
{"bits_per_raw_sample", NULL, OFFSET(bits_per_raw_sample), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX},
{"channel_layout", NULL, OFFSET(channel_layout), AV_OPT_TYPE_UINT64, {.i64 = DEFAULT }, 0, UINT64_MAX, A|E|D, "channel_layout"},
{"request_channel_layout", NULL, OFFSET(request_channel_layout), AV_OPT_TYPE_UINT64, {.i64 = DEFAULT }, 0, UINT64_MAX, A|D, "request_channel_layout"},
{"rc_max_vbv_use", NULL, OFFSET(rc_max_available_vbv_use), AV_OPT_TYPE_FLOAT, {.dbl = 0 }, 0.0, FLT_MAX, V|E},
{"rc_min_vbv_use", NULL, OFFSET(rc_min_vbv_overflow_use),  AV_OPT_TYPE_FLOAT, {.dbl = 3 },     0.0, FLT_MAX, V|E},
{"ticks_per_frame", NULL, OFFSET(ticks_per_frame), AV_OPT_TYPE_INT, {.i64 = 1 }, 1, INT_MAX, A|V|E|D},
{"color_primaries", "color primaries", OFFSET(color_primaries), AV_OPT_TYPE_INT, {.i64 = AVCOL_PRI_UNSPECIFIED }, 1, INT_MAX, V|E|D, "color_primaries_type"},
{"bt709",       "BT.709",         0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_BT709 },        INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"unknown",     "Unspecified",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_UNSPECIFIED },  INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"bt470m",      "BT.470 M",       0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_BT470M },       INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"bt470bg",     "BT.470 BG",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_BT470BG },      INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"smpte170m",   "SMPTE 170 M",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_SMPTE170M },    INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"smpte240m",   "SMPTE 240 M",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_SMPTE240M },    INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"film",        "Film",           0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_FILM },         INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"bt2020",      "BT.2020",        0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_BT2020 },       INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"smpte428",    "SMPTE 428-1",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_SMPTE428 },     INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"smpte428_1",  "SMPTE 428-1",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_SMPTE428 },     INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"smpte431",    "SMPTE 431-2",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_SMPTE431 },     INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"smpte432",    "SMPTE 422-1",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_SMPTE432 },     INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"jedec-p22",   "JEDEC P22",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_JEDEC_P22 },    INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"unspecified", "Unspecified",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_PRI_UNSPECIFIED },  INT_MIN, INT_MAX, V|E|D, "color_primaries_type"},
{"color_trc", "color transfer characteristics", OFFSET(color_trc), AV_OPT_TYPE_INT, {.i64 = AVCOL_TRC_UNSPECIFIED }, 1, INT_MAX, V|E|D, "color_trc_type"},
{"bt709",        "BT.709",           0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_BT709 },        INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"unknown",      "Unspecified",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_UNSPECIFIED },  INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"gamma22",      "BT.470 M",         0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_GAMMA22 },      INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"gamma28",      "BT.470 BG",        0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_GAMMA28 },      INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"smpte170m",    "SMPTE 170 M",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_SMPTE170M },    INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"smpte240m",    "SMPTE 240 M",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_SMPTE240M },    INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"linear",       "Linear",           0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_LINEAR },       INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"log100",       "Log",              0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_LOG },          INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"log316",       "Log square root",  0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_LOG_SQRT },     INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"iec61966-2-4", "IEC 61966-2-4",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_IEC61966_2_4 }, INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"bt1361e",      "BT.1361",          0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_BT1361_ECG },   INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"iec61966-2-1", "IEC 61966-2-1",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_IEC61966_2_1 }, INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"bt2020-10",    "BT.2020 - 10 bit", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_BT2020_10 },    INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"bt2020-12",    "BT.2020 - 12 bit", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_BT2020_12 },    INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"smpte2084",    "SMPTE 2084",       0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_SMPTE2084 },    INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"smpte428",     "SMPTE 428-1",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_SMPTE428 },     INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"arib-std-b67", "ARIB STD-B67",     0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_ARIB_STD_B67 }, INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"unspecified",  "Unspecified",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_UNSPECIFIED },  INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"log",          "Log",              0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_LOG },          INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"log_sqrt",     "Log square root",  0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_LOG_SQRT },     INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"iec61966_2_4", "IEC 61966-2-4",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_IEC61966_2_4 }, INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"bt1361",       "BT.1361",          0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_BT1361_ECG },   INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"iec61966_2_1", "IEC 61966-2-1",    0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_IEC61966_2_1 }, INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"bt2020_10bit", "BT.2020 - 10 bit", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_BT2020_10 },    INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"bt2020_12bit", "BT.2020 - 12 bit", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_BT2020_12 },    INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"smpte428_1",   "SMPTE 428-1",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_SMPTE428 },     INT_MIN, INT_MAX, V|E|D, "color_trc_type"},
{"colorspace", "color space", OFFSET(colorspace), AV_OPT_TYPE_INT, {.i64 = AVCOL_SPC_UNSPECIFIED }, 0, INT_MAX, V|E|D, "colorspace_type"},
{"rgb",         "RGB",         0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_RGB },         INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"bt709",       "BT.709",      0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_BT709 },       INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"unknown",     "Unspecified", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_UNSPECIFIED }, INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"fcc",         "FCC",         0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_FCC },         INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"bt470bg",     "BT.470 BG",   0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_BT470BG },     INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"smpte170m",   "SMPTE 170 M", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_SMPTE170M },   INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"smpte240m",   "SMPTE 240 M", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_SMPTE240M },   INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"ycgco",       "YCGCO",       0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_YCGCO },       INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"bt2020nc",    "BT.2020 NCL", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_BT2020_NCL },  INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"bt2020c",     "BT.2020 CL",  0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_BT2020_CL },   INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"smpte2085",   "SMPTE 2085",  0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_SMPTE2085 },   INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"unspecified", "Unspecified", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_UNSPECIFIED }, INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"ycocg",       "YCGCO",       0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_YCGCO },       INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"bt2020_ncl",  "BT.2020 NCL", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_BT2020_NCL },  INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"bt2020_cl",   "BT.2020 CL",  0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_SPC_BT2020_CL },   INT_MIN, INT_MAX, V|E|D, "colorspace_type"},
{"color_range", "color range", OFFSET(color_range), AV_OPT_TYPE_INT, {.i64 = AVCOL_RANGE_UNSPECIFIED }, 0, INT_MAX, V|E|D, "color_range_type"},
{"unknown", "Unspecified",     0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_RANGE_UNSPECIFIED }, INT_MIN, INT_MAX, V|E|D, "color_range_type"},
{"tv", "MPEG (219*2^(n-8))",   0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_RANGE_MPEG },        INT_MIN, INT_MAX, V|E|D, "color_range_type"},
{"pc", "JPEG (2^n-1)",         0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_RANGE_JPEG },        INT_MIN, INT_MAX, V|E|D, "color_range_type"},
{"unspecified", "Unspecified", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_RANGE_UNSPECIFIED }, INT_MIN, INT_MAX, V|E|D, "color_range_type"},
{"mpeg", "MPEG (219*2^(n-8))", 0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_RANGE_MPEG },        INT_MIN, INT_MAX, V|E|D, "color_range_type"},
{"jpeg", "JPEG (2^n-1)",       0, AV_OPT_TYPE_CONST, {.i64 = AVCOL_RANGE_JPEG },        INT_MIN, INT_MAX, V|E|D, "color_range_type"},
{"chroma_sample_location", "chroma sample location", OFFSET(chroma_sample_location), AV_OPT_TYPE_INT, {.i64 = AVCHROMA_LOC_UNSPECIFIED }, 0, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"unknown",     "Unspecified", 0, AV_OPT_TYPE_CONST, {.i64 = AVCHROMA_LOC_UNSPECIFIED }, INT_MIN, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"left",        "Left",        0, AV_OPT_TYPE_CONST, {.i64 = AVCHROMA_LOC_LEFT },        INT_MIN, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"center",      "Center",      0, AV_OPT_TYPE_CONST, {.i64 = AVCHROMA_LOC_CENTER },      INT_MIN, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"topleft",     "Top-left",    0, AV_OPT_TYPE_CONST, {.i64 = AVCHROMA_LOC_TOPLEFT },     INT_MIN, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"top",         "Top",         0, AV_OPT_TYPE_CONST, {.i64 = AVCHROMA_LOC_TOP },         INT_MIN, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"bottomleft",  "Bottom-left", 0, AV_OPT_TYPE_CONST, {.i64 = AVCHROMA_LOC_BOTTOMLEFT },  INT_MIN, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"bottom",      "Bottom",      0, AV_OPT_TYPE_CONST, {.i64 = AVCHROMA_LOC_BOTTOM },      INT_MIN, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"unspecified", "Unspecified", 0, AV_OPT_TYPE_CONST, {.i64 = AVCHROMA_LOC_UNSPECIFIED }, INT_MIN, INT_MAX, V|E|D, "chroma_sample_location_type"},
{"log_level_offset", "set the log level offset", OFFSET(log_level_offset), AV_OPT_TYPE_INT, {.i64 = 0 }, INT_MIN, INT_MAX },
{"slices", "set the number of slices, used in parallelized encoding", OFFSET(slices), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, INT_MAX, V|E},
{"thread_type", "select multithreading type", OFFSET(thread_type), AV_OPT_TYPE_FLAGS, {.i64 = FF_THREAD_SLICE|FF_THREAD_FRAME }, 0, INT_MAX, V|A|E|D, "thread_type"},
{"slice", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_THREAD_SLICE }, INT_MIN, INT_MAX, V|E|D, "thread_type"},
{"frame", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_THREAD_FRAME }, INT_MIN, INT_MAX, V|E|D, "thread_type"},
{"audio_service_type", "audio service type", OFFSET(audio_service_type), AV_OPT_TYPE_INT, {.i64 = AV_AUDIO_SERVICE_TYPE_MAIN }, 0, AV_AUDIO_SERVICE_TYPE_NB-1, A|E, "audio_service_type"},
{"ma", "Main Audio Service", 0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_MAIN },              INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"ef", "Effects",            0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_EFFECTS },           INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"vi", "Visually Impaired",  0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_VISUALLY_IMPAIRED }, INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"hi", "Hearing Impaired",   0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_HEARING_IMPAIRED },  INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"di", "Dialogue",           0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_DIALOGUE },          INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"co", "Commentary",         0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_COMMENTARY },        INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"em", "Emergency",          0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_EMERGENCY },         INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"vo", "Voice Over",         0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_VOICE_OVER },        INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"ka", "Karaoke",            0, AV_OPT_TYPE_CONST, {.i64 = AV_AUDIO_SERVICE_TYPE_KARAOKE },           INT_MIN, INT_MAX, A|E, "audio_service_type"},
{"request_sample_fmt", "sample format audio decoders should prefer", OFFSET(request_sample_fmt), AV_OPT_TYPE_SAMPLE_FMT, {.i64=AV_SAMPLE_FMT_NONE}, -1, INT_MAX, A|D, "request_sample_fmt"},
{"pkt_timebase", NULL, OFFSET(pkt_timebase), AV_OPT_TYPE_RATIONAL, {.dbl = 0 }, 0, INT_MAX, 0},
{"sub_charenc", "set input text subtitles character encoding", OFFSET(sub_charenc), AV_OPT_TYPE_STRING, {.str = NULL}, CHAR_MIN, CHAR_MAX, S|D},
{"sub_charenc_mode", "set input text subtitles character encoding mode", OFFSET(sub_charenc_mode), AV_OPT_TYPE_FLAGS, {.i64 = FF_SUB_CHARENC_MODE_AUTOMATIC}, -1, INT_MAX, S|D, "sub_charenc_mode"},
{"do_nothing",  NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_SUB_CHARENC_MODE_DO_NOTHING},  INT_MIN, INT_MAX, S|D, "sub_charenc_mode"},
{"auto",        NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_SUB_CHARENC_MODE_AUTOMATIC},   INT_MIN, INT_MAX, S|D, "sub_charenc_mode"},
{"pre_decoder", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_SUB_CHARENC_MODE_PRE_DECODER}, INT_MIN, INT_MAX, S|D, "sub_charenc_mode"},
{"ignore",      NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_SUB_CHARENC_MODE_IGNORE},      INT_MIN, INT_MAX, S|D, "sub_charenc_mode"},
#if FF_API_ASS_TIMING
{"sub_text_format", "set decoded text subtitle format", OFFSET(sub_text_format), AV_OPT_TYPE_INT, {.i64 = FF_SUB_TEXT_FMT_ASS_WITH_TIMINGS}, 0, 1, S|D, "sub_text_format"},
#else
{"sub_text_format", "set decoded text subtitle format", OFFSET(sub_text_format), AV_OPT_TYPE_INT, {.i64 = FF_SUB_TEXT_FMT_ASS}, 0, 1, S|D, "sub_text_format"},
#endif
{"ass",              NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_SUB_TEXT_FMT_ASS},              INT_MIN, INT_MAX, S|D, "sub_text_format"},
#if FF_API_ASS_TIMING
{"ass_with_timings", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_SUB_TEXT_FMT_ASS_WITH_TIMINGS}, INT_MIN, INT_MAX, S|D, "sub_text_format"},
#endif
{"refcounted_frames", NULL, OFFSET(refcounted_frames), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, A|V|D },
#if FF_API_SIDEDATA_ONLY_PKT
{"side_data_only_packets", NULL, OFFSET(side_data_only_packets), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, A|V|E },
#endif
{"apply_cropping", NULL, OFFSET(apply_cropping), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, V | D },
{"skip_alpha", "Skip processing alpha", OFFSET(skip_alpha), AV_OPT_TYPE_BOOL, {.i64 = 0 }, 0, 1, V|D },
{"field_order", "Field order", OFFSET(field_order), AV_OPT_TYPE_INT, {.i64 = AV_FIELD_UNKNOWN }, 0, 5, V|D|E, "field_order" },
{"progressive", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = AV_FIELD_PROGRESSIVE }, 0, 0, V|D|E, "field_order" },
{"tt", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = AV_FIELD_TT }, 0, 0, V|D|E, "field_order" },
{"bb", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = AV_FIELD_BB }, 0, 0, V|D|E, "field_order" },
{"tb", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = AV_FIELD_TB }, 0, 0, V|D|E, "field_order" },
{"bt", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = AV_FIELD_BT }, 0, 0, V|D|E, "field_order" },
{"dump_separator", "set information dump field separator", OFFSET(dump_separator), AV_OPT_TYPE_STRING, {.str = NULL}, CHAR_MIN, CHAR_MAX, A|V|S|D|E},
{"codec_whitelist", "List of decoders that are allowed to be used", OFFSET(codec_whitelist), AV_OPT_TYPE_STRING, { .str = NULL },  CHAR_MIN, CHAR_MAX, A|V|S|D },
{"pixel_format", "set pixel format", OFFSET(pix_fmt), AV_OPT_TYPE_PIXEL_FMT, {.i64=AV_PIX_FMT_NONE}, -1, INT_MAX, 0 },
{"video_size", "set video size", OFFSET(width), AV_OPT_TYPE_IMAGE_SIZE, {.str=NULL}, 0, INT_MAX, 0 },
{"max_pixels", "Maximum number of pixels", OFFSET(max_pixels), AV_OPT_TYPE_INT64, {.i64 = INT_MAX }, 0, INT_MAX, A|V|S|D|E },
{"hwaccel_flags", NULL, OFFSET(hwaccel_flags), AV_OPT_TYPE_FLAGS, {.i64 = AV_HWACCEL_FLAG_IGNORE_LEVEL }, 0, UINT_MAX, V|D, "hwaccel_flags"},
{"ignore_level", "ignore level even if the codec level used is unknown or higher than the maximum supported level reported by the hardware driver", 0, AV_OPT_TYPE_CONST, { .i64 = AV_HWACCEL_FLAG_IGNORE_LEVEL }, INT_MIN, INT_MAX, V | D, "hwaccel_flags" },
{"allow_high_depth", "allow to output YUV pixel formats with a different chroma sampling than 4:2:0 and/or other than 8 bits per component", 0, AV_OPT_TYPE_CONST, {.i64 = AV_HWACCEL_FLAG_ALLOW_HIGH_DEPTH }, INT_MIN, INT_MAX, V | D, "hwaccel_flags"},
{"allow_profile_mismatch", "attempt to decode anyway if HW accelerated decoder's supported profiles do not exactly match the stream", 0, AV_OPT_TYPE_CONST, {.i64 = AV_HWACCEL_FLAG_ALLOW_PROFILE_MISMATCH }, INT_MIN, INT_MAX, V | D, "hwaccel_flags"},
{"extra_hw_frames", "Number of extra hardware frames to allocate for the user", OFFSET(extra_hw_frames), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, V|D },
{NULL},
};

2.3AVFrame中的AVClass

AVFrame 中的AVClass定义位于libavcodec\options.c中，是一个名称为av_frame_class的静态结构体。如下所示。

static const AVClass av_frame_class = {
    .class_name              = "AVFrame",
    .item_name               = NULL,
    .option                  = frame_options,
    .version                 = LIBAVUTIL_VERSION_INT,
};

option字段则指向一个元素个数极多的静态数组frame_options。frame_options定义如下所示。

static const AVOption frame_options[]={
{"best_effort_timestamp", "", FOFFSET(best_effort_timestamp), AV_OPT_TYPE_INT64, {.i64 = AV_NOPTS_VALUE }, INT64_MIN, INT64_MAX, 0},
{"pkt_pos", "", FOFFSET(pkt_pos), AV_OPT_TYPE_INT64, {.i64 = -1 }, INT64_MIN, INT64_MAX, 0},
{"pkt_size", "", FOFFSET(pkt_size), AV_OPT_TYPE_INT64, {.i64 = -1 }, INT64_MIN, INT64_MAX, 0},
{"sample_aspect_ratio", "", FOFFSET(sample_aspect_ratio), AV_OPT_TYPE_RATIONAL, {.dbl = 0 }, 0, INT_MAX, 0},
{"width", "", FOFFSET(width), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, INT_MAX, 0},
{"height", "", FOFFSET(height), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, INT_MAX, 0},
{"format", "", FOFFSET(format), AV_OPT_TYPE_INT, {.i64 = -1 }, 0, INT_MAX, 0},
{"channel_layout", "", FOFFSET(channel_layout), AV_OPT_TYPE_INT64, {.i64 = 0 }, 0, INT64_MAX, 0},
{"sample_rate", "", FOFFSET(sample_rate), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, INT_MAX, 0},
{NULL},
};

3、AVClass有关的API

与AVClass相关的API很少。AVFormatContext提供了一个获取当前AVClass的函数avformat_get_class()。它的代码很简单，直接返回全局静态变量av_format_context_class。定义如下所示。

const AVClass *avformat_get_class(void)
{
    return &av_format_context_class;
}

同样，AVCodecContext也提供了一个获取当前AVClass的函数avcodec_get_class()。它直接返回静态变量av_codec_context_class。定义如下所示。

const AVClass *avcodec_get_class(void)
{
    return &av_codec_context_class;
}

4、参考文献

1、https://blog.csdn.net/leixiaohua1020/article/details/44268323

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