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一、FFmpeg基础介绍
1.FFmpeg 介绍
FFmpeg它是一套开源计算机程序，可用于记录、转换数字音频和视频，并将其转换为流程。LGPL或GPL许可证。它提供了音视频提供了完整的录制、转换和解决方案。它包含了非常先进的音频/视频编解码库。
2.FFmpeg 组成
- libavformat：用于各种音视频[封装格式](https://baike.baidu.com/item/包装格式)的生成和分析包括获取解码所需的信息，生成解码上下文结构和读取音视频帧；
- libavcodec：编解码各种类型的声音/图像；
- libavutil：包含一些公共工具函数；
- libswscale：用于视频场景比例缩放和色彩映射转换；
- libpostproc：用于后期效果处理；
- ffmpeg：该项目提供的工具可用于格式转换、解码或[电视卡](https://baike.baidu.com/item/电视卡)即时编码等；
- ffsever：一个 HTTP 多媒体即时广播串流服务器；
- ffplay：使用简单的播放器ffmpeg 通过库分析和解码SDL显示；
3.FFmpeg包括类库说明
3.1 类库说明
- libavformat - 用于各种音视频封装格式的生成和解析，包括获取解码所需信息、读取音视频数据等功能。各种流媒体协议代码(如rtmpproto.c等)和音视频格式(解)复用代码(如flvdec.c、flvenc.c等)都位于目录下。
- libavcodec - 各种格式的音视频编解码。各种格式的编解码代码(如aacenc.c、aacdec.c等)都位于目录下。
- libavutil - 使用库包括一些公共工具函数，包括算数操作、字符操作等。
- libswscale - 提供原始视频的比例缩放、色彩映射转换、图像色彩空间或格式转换。
- libswresample - 提供音频重采样、采样格式转换、混合等功能。
- libavfilter - 各种音视频滤波器。
- libpostproc - 用于后期效果处理，如图像果处理。
- libavdevice - 音视频采集、加速和显示用于硬件。
假如没有阅读FFmpeg建议优先阅读代码经验libavformat、libavcodec以及libavutil下面的代码，它们提供了音视频开发的最基本功能，应用范围也是最广的。
3.2 常用结构
FFmpeg根据功能，最常用的数据结构大致可以分为以下类别（以下代码行数）branch: origin/release/3.4为准)：
(1)封装格式
- AVFormatContext - 它描述了媒体文件的构成和基本信息，是整体领先的基本结构，贯穿程序，许多函数应作为参数；
- AVInputFormat - 解复用器对象，每种封装格式作为输入(例如FLV、MP4、TS等)对应结构体，如libavformat/flvdec.c的ff_flv_demuxer；
- AVOutputFormat - 复用器对象，每个封装格式作为输出(例如FLV, MP4、TS等)对应该结构体，如libavformat/flvenc.c的ff_flv_muxer；
- AVStream - 描述视频/音频流的相关数据信息。
（2）编解码
- AVCodecContext - 描述编解码器上下文的数据结构，包含编解码器所需的许多参数信息；
- AVCodec - 编解码对象，每个编解码格式(如H.264、AAC等)对应该结构体，如libavcodec/aacdec.c的ff_aac_decoder。每个AVCodecContext中含有一个AVCodec；
- AVCodecParameters - 编解码参数，每个AVStream中都含有一个AVCodecParameters，用于存储当前流的编解码参数。
(3)网络协议
- AVIOContext - 管理输入输出数据的结构；
- URLProtocol - 描述了音视频数据传输中使用的各种传输协议(如HTTP、RTMP)等等，会对应一个URLProtocol结构，如libavformat/http.c中的ff_http_protocol；
- URLContext - 包装协议对象和协议操作对象。
(4)数据存储
- AVPacket - 存储编码和解码前的压缩数据，即ES数据；
- AVFrame - 存储编码前、解码后的原始数据，如YUV格式视频数据或PCM音频数据格式等；
4.ffmpeg相关术语
(1)容器/文件（Container/File）**：即具体格式的多媒体文件，如MP4，flv，mov等。
（2） 媒体流（Stream）**：表示时间轴上的连续数据，如声音数据、视频数据或字母数据，可以压缩或非压缩。压缩数据需要与特定的编解码器相关联。
（3） 数据帧/数据包（Frame/Packet）**：通常，媒体流由大量的数据帧组成。对于压缩数据，帧对应编解码器的最小处理单元，分为不同媒体流的数据帧交错存储和容器。
（4） 编解码器**：编解码器实现压缩数据与原始数据之间的相互转换。
前面介绍的术语是FFmpeg抽象概念。
（1）AVFormatContext**：是对容器或媒体文件层次的抽象。
（2） AVStream**：多路流(音频流、视频流、字幕流)在文件中包含，AVStream 对流抽象。
（3） AVCodecContext 与 AVCodec**：这条路流的编码格式将在每条路流中描述。编解码器格式和编解码器的抽象是AVCodecContext 与 AVCodec。
（4） AVPacket 与 AVFrame**：对于编码器或解码器的输入输出部分，即压缩数据和原始数据的抽象AVPacket与AVFrame。
**5. AVFilte**r：除编解码外，音视频的处理必须针对原始数据，即AVFrame用于处理AVFilter。
二、FFmpeg结构体
1.AVFormatContext结构体
typedef struct AVFormatContext { /** * A class for logging and @ref avoptions. Set by avformat_alloc_context(). * Exports (de)muxer private options if they exist. */ const AVClass *av_class; /** * The input container format. * * Demuxing only, set by avformat_open_input(). */ ff_const59 struct AVInputFormat *iformat; /** * The output container format. * * Muxing only, must be set by the caller before avformat_write_header(). */ ff_const59 struct AVOutputFormat *oformat; /** * Format private data. This is an AVOptions-enabled struct * if and only if iformat/oformat.priv_class is not NULL. * * - muxing: set by avformat_write_header() * - demuxing: set by avformat_open_input() */ void *priv_data; /** * I/O context. * * - demuxing: either set by the user before avformat_open_input() (then * the user must close it manually) or set by avformat_open_input(). * - muxing: set by the user before avformat_write_header(). The caller must * take care of closing / freeing the IO context. * * Do NOT set this field if AVFMT_NOILE flag is set in
* iformat/oformat.flags. In such a case, the (de)muxer will handle
* I/O in some other way and this field will be NULL.
*/
AVIOContext *pb;
/* stream info */
/**
* Flags signalling stream properties. A combination of AVFMTCTX_*.
* Set by libavformat.
*/
int ctx_flags;
/**
* Number of elements in AVFormatContext.streams.
*
* Set by avformat_new_stream(), must not be modified by any other code.
*/
unsigned int nb_streams;
/**
* A list of all streams in the file. New streams are created with
* avformat_new_stream().
*
* - demuxing: streams are created by libavformat in avformat_open_input().
* If AVFMTCTX_NOHEADER is set in ctx_flags, then new streams may also
* appear in av_read_frame().
* - muxing: streams are created by the user before avformat_write_header().
*
* Freed by libavformat in avformat_free_context().
*/
AVStream **streams;
#if FF_API_FORMAT_FILENAME
/**
* input or output filename
*
* - demuxing: set by avformat_open_input()
* - muxing: may be set by the caller before avformat_write_header()
*
* @deprecated Use url instead.
*/
attribute_deprecated
char filename[1024];
#endif
/**
* input or output URL. Unlike the old filename field, this field has no
* length restriction.
*
* - demuxing: set by avformat_open_input(), initialized to an empty
* string if url parameter was NULL in avformat_open_input().
* - muxing: may be set by the caller before calling avformat_write_header()
* (or avformat_init_output() if that is called first) to a string
* which is freeable by av_free(). Set to an empty string if it
* was NULL in avformat_init_output().
*
* Freed by libavformat in avformat_free_context().
*/
char *url;
/**
* Position of the first frame of the component, in
* AV_TIME_BASE fractional seconds. NEVER set this value directly:
* It is deduced from the AVStream values.
*
* Demuxing only, set by libavformat.
*/
int64_t start_time;
/**
* Duration of the stream, in AV_TIME_BASE fractional
* seconds. Only set this value if you know none of the individual stream
* durations and also do not set any of them. This is deduced from the
* AVStream values if not set.
*
* Demuxing only, set by libavformat.
*/
int64_t duration;
/**
* Total stream bitrate in bit/s, 0 if not
* available. Never set it directly if the file_size and the
* duration are known as FFmpeg can compute it automatically.
*/
int64_t bit_rate;
unsigned int packet_size;
int max_delay;
/**
* Flags modifying the (de)muxer behaviour. A combination of AVFMT_FLAG_*.
* Set by the user before avformat_open_input() / avformat_write_header().
*/
int flags;
#define AVFMT_FLAG_GENPTS 0x0001 ///< Generate missing pts even if it requires parsing future frames.
#define AVFMT_FLAG_IGNIDX 0x0002 ///< Ignore index.
#define AVFMT_FLAG_NONBLOCK 0x0004 ///< Do not block when reading packets from input.
#define AVFMT_FLAG_IGNDTS 0x0008 ///< Ignore DTS on frames that contain both DTS & PTS
#define AVFMT_FLAG_NOFILLIN 0x0010 ///< Do not infer any values from other values, just return what is stored in the container
#define AVFMT_FLAG_NOPARSE 0x0020 ///< Do not use AVParsers, you also must set AVFMT_FLAG_NOFILLIN as the fillin code works on frames and no parsing -> no frames. Also seeking to frames can not work if parsing to find frame boundaries has been disabled
#define AVFMT_FLAG_NOBUFFER 0x0040 ///< Do not buffer frames when possible
#define AVFMT_FLAG_CUSTOM_IO 0x0080 ///< The caller has supplied a custom AVIOContext, don't avio_close() it.
#define AVFMT_FLAG_DISCARD_CORRUPT 0x0100 ///< Discard frames marked corrupted
#define AVFMT_FLAG_FLUSH_PACKETS 0x0200 ///< Flush the AVIOContext every packet.
/**
* When muxing, try to avoid writing any random/volatile data to the output.
* This includes any random IDs, real-time timestamps/dates, muxer version, etc.
*
* This flag is mainly intended for testing.
*/
#define AVFMT_FLAG_BITEXACT 0x0400
#if FF_API_LAVF_MP4A_LATM
#define AVFMT_FLAG_MP4A_LATM 0x8000 ///< Deprecated, does nothing.
#endif
#define AVFMT_FLAG_SORT_DTS 0x10000 ///< try to interleave outputted packets by dts (using this flag can slow demuxing down)
#if FF_API_LAVF_PRIV_OPT
#define AVFMT_FLAG_PRIV_OPT 0x20000 ///< Enable use of private options by delaying codec open (deprecated, will do nothing once av_demuxer_open() is removed)
#endif
#if FF_API_LAVF_KEEPSIDE_FLAG
#define AVFMT_FLAG_KEEP_SIDE_DATA 0x40000 ///< Deprecated, does nothing.
#endif
#define AVFMT_FLAG_FAST_SEEK 0x80000 ///< Enable fast, but inaccurate seeks for some formats
#define AVFMT_FLAG_SHORTEST 0x100000 ///< Stop muxing when the shortest stream stops.
#define AVFMT_FLAG_AUTO_BSF 0x200000 ///< Add bitstream filters as requested by the muxer
/**
* Maximum size of the data read from input for determining
* the input container format.
* Demuxing only, set by the caller before avformat_open_input().
*/
int64_t probesize;
/**
* Maximum duration (in AV_TIME_BASE units) of the data read
* from input in avformat_find_stream_info().
* Demuxing only, set by the caller before avformat_find_stream_info().
* Can be set to 0 to let avformat choose using a heuristic.
*/
int64_t max_analyze_duration;
const uint8_t *key;
int keylen;
unsigned int nb_programs;
AVProgram **programs;
/**
* Forced video codec_id.
* Demuxing: Set by user.
*/
enum AVCodecID video_codec_id;
/**
* Forced audio codec_id.
* Demuxing: Set by user.
*/
enum AVCodecID audio_codec_id;
/**
* Forced subtitle codec_id.
* Demuxing: Set by user.
*/
enum AVCodecID subtitle_codec_id;
/**
* Maximum amount of memory in bytes to use for the index of each stream.
* If the index exceeds this size, entries will be discarded as
* needed to maintain a smaller size. This can lead to slower or less
* accurate seeking (depends on demuxer).
* Demuxers for which a full in-memory index is mandatory will ignore
* this.
* - muxing: unused
* - demuxing: set by user
*/
unsigned int max_index_size;
/**
* Maximum amount of memory in bytes to use for buffering frames
* obtained from realtime capture devices.
*/
unsigned int max_picture_buffer;
/**
* Number of chapters in AVChapter array.
* When muxing, chapters are normally written in the file header,
* so nb_chapters should normally be initialized before write_header
* is called. Some muxers (e.g. mov and mkv) can also write chapters
* in the trailer. To write chapters in the trailer, nb_chapters
* must be zero when write_header is called and non-zero when
* write_trailer is called.
* - muxing: set by user
* - demuxing: set by libavformat
*/
unsigned int nb_chapters;
AVChapter **chapters;
/**
* Metadata that applies to the whole file.
*
* - demuxing: set by libavformat in avformat_open_input()
* - muxing: may be set by the caller before avformat_write_header()
*
* Freed by libavformat in avformat_free_context().
*/
AVDictionary *metadata;
/**
* Start time of the stream in real world time, in microseconds
* since the Unix epoch (00:00 1st January 1970). That is, pts=0 in the
* stream was captured at this real world time.
* - muxing: Set by the caller before avformat_write_header(). If set to
* either 0 or AV_NOPTS_VALUE, then the current wall-time will
* be used.
* - demuxing: Set by libavformat. AV_NOPTS_VALUE if unknown. Note that
* the value may become known after some number of frames
* have been received.
*/
int64_t start_time_realtime;
/**
* The number of frames used for determining the framerate in
* avformat_find_stream_info().
* Demuxing only, set by the caller before avformat_find_stream_info().
*/
int fps_probe_size;
/**
* Error recognition; higher values will detect more errors but may
* misdetect some more or less valid parts as errors.
* Demuxing only, set by the caller before avformat_open_input().
*/
int error_recognition;
/**
* Custom interrupt callbacks for the I/O layer.
*
* demuxing: set by the user before avformat_open_input().
* muxing: set by the user before avformat_write_header()
* (mainly useful for AVFMT_NOFILE formats). The callback
* should also be passed to avio_open2() if it's used to
* open the file.
*/
AVIOInterruptCB interrupt_callback;
/**
* Flags to enable debugging.
*/
int debug;
#define FF_FDEBUG_TS 0x0001
/**
* Maximum buffering duration for interleaving.
*
* To ensure all the streams are interleaved correctly,
* av_interleaved_write_frame() will wait until it has at least one packet
* for each stream before actually writing any packets to the output file.
* When some streams are "sparse" (i.e. there are large gaps between
* successive packets), this can result in excessive buffering.
*
* This field specifies the maximum difference between the timestamps of the
* first and the last packet in the muxing queue, above which libavformat
* will output a packet regardless of whether it has queued a packet for all
* the streams.
*
* Muxing only, set by the caller before avformat_write_header().
*/
int64_t max_interleave_delta;
/**
* Allow non-standard and experimental extension
* @see AVCodecContext.strict_std_compliance
*/
int strict_std_compliance;
/**
* Flags indicating events happening on the file, a combination of
* AVFMT_EVENT_FLAG_*.
*
* - demuxing: may be set by the demuxer in avformat_open_input(),
* avformat_find_stream_info() and av_read_frame(). Flags must be cleared
* by the user once the event has been handled.
* - muxing: may be set by the user after avformat_write_header() to
* indicate a user-triggered event. The muxer will clear the flags for
* events it has handled in av_[interleaved]_write_frame().
*/
int event_flags;
/**
* - demuxing: the demuxer read new metadata from the file and updated
* AVFormatContext.metadata accordingly
* - muxing: the user updated AVFormatContext.metadata and wishes the muxer to
* write it into the file
*/
#define AVFMT_EVENT_FLAG_METADATA_UPDATED 0x0001
/**
* Maximum number of packets to read while waiting for the first timestamp.
* Decoding only.
*/
int max_ts_probe;
/**
* Avoid negative timestamps during muxing.
* Any value of the AVFMT_AVOID_NEG_TS_* constants.
* Note, this only works when using av_interleaved_write_frame. (interleave_packet_per_dts is in use)
* - muxing: Set by user
* - demuxing: unused
*/
int avoid_negative_ts;
#define AVFMT_AVOID_NEG_TS_AUTO -1 ///< Enabled when required by target format
#define AVFMT_AVOID_NEG_TS_MAKE_NON_NEGATIVE 1 ///< Shift timestamps so they are non negative
#define AVFMT_AVOID_NEG_TS_MAKE_ZERO 2 ///< Shift timestamps so that they start at 0
/**
* Transport stream id.
* This will be moved into demuxer private options. Thus no API/ABI compatibility
*/
int ts_id;
/**
* Audio preload in microseconds.
* Note, not all formats support this and unpredictable things may happen if it is used when not supported.
* - encoding: Set by user
* - decoding: unused
*/
int audio_preload;
/**
* Max chunk time in microseconds.
* Note, not all formats support this and unpredictable things may happen if it is used when not supported.
* - encoding: Set by user
* - decoding: unused
*/
int max_chunk_duration;
/**
* Max chunk size in bytes
* Note, not all formats support this and unpredictable things may happen if it is used when not supported.
* - encoding: Set by user
* - decoding: unused
*/
int max_chunk_size;
/**
* forces the use of wallclock timestamps as pts/dts of packets
* This has undefined results in the presence of B frames.
* - encoding: unused
* - decoding: Set by user
*/
int use_wallclock_as_timestamps;
/**
* avio flags, used to force AVIO_FLAG_DIRECT.
* - encoding: unused
* - decoding: Set by user
*/
int avio_flags;
/**
* The duration field can be estimated through various ways, and this field can be used
* to know how the duration was estimated.
* - encoding: unused
* - decoding: Read by user
*/
enum AVDurationEstimationMethod duration_estimation_method;
/**
* Skip initial bytes when opening stream
* - encoding: unused
* - decoding: Set by user
*/
int64_t skip_initial_bytes;
/**
* Correct single timestamp overflows
* - encoding: unused
* - decoding: Set by user
*/
unsigned int correct_ts_overflow;
/**
* Force seeking to any (also non key) frames.
* - encoding: unused
* - decoding: Set by user
*/
int seek2any;
/**
* Flush the I/O context after each packet.
* - encoding: Set by user
* - decoding: unused
*/
int flush_packets;
/**
* format probing score.
* The maximal score is AVPROBE_SCORE_MAX, its set when the demuxer probes
* the format.
* - encoding: unused
* - decoding: set by avformat, read by user
*/
int probe_score;
/**
* number of bytes to read maximally to identify format.
* - encoding: unused
* - decoding: set by user
*/
int format_probesize;
/**
* ',' separated list of allowed decoders.
* If NULL then all are allowed
* - encoding: unused
* - decoding: set by user
*/
char *codec_whitelist;
/**
* ',' separated list of allowed demuxers.
* If NULL then all are allowed
* - encoding: unused
* - decoding: set by user
*/
char *format_whitelist;
/**
* An opaque field for libavformat internal usage.
* Must not be accessed in any way by callers.
*/
AVFormatInternal *internal;
/**
* IO repositioned flag.
* This is set by avformat when the underlaying IO context read pointer
* is repositioned, for example when doing byte based seeking.
* Demuxers can use the flag to detect such changes.
*/
int io_repositioned;
/**
* Forced video codec.
* This allows forcing a specific decoder, even when there are multiple with
* the same codec_id.
* Demuxing: Set by user
*/
AVCodec *video_codec;
/**
* Forced audio codec.
* This allows forcing a specific decoder, even when there are multiple with
* the same codec_id.
* Demuxing: Set by user
*/
AVCodec *audio_codec;
/**
* Forced subtitle codec.
* This allows forcing a specific decoder, even when there are multiple with
* the same codec_id.
* Demuxing: Set by user
*/
AVCodec *subtitle_codec;
/**
* Forced data codec.
* This allows forcing a specific decoder, even when there are multiple with
* the same codec_id.
* Demuxing: Set by user
*/
AVCodec *data_codec;
/**
* Number of bytes to be written as padding in a metadata header.
* Demuxing: Unused.
* Muxing: Set by user via av_format_set_metadata_header_padding.
*/
int metadata_header_padding;
/**
* User data.
* This is a place for some private data of the user.
*/
void *opaque;
/**
* Callback used by devices to communicate with application.
*/
av_format_control_message control_message_cb;
/**
* Output timestamp offset, in microseconds.
* Muxing: set by user
*/
int64_t output_ts_offset;
/**
* dump format separator.
* can be ", " or "\n " or anything else
* - muxing: Set by user.
* - demuxing: Set by user.
*/
uint8_t *dump_separator;
/**
* Forced Data codec_id.
* Demuxing: Set by user.
*/
enum AVCodecID data_codec_id;
#if FF_API_OLD_OPEN_CALLBACKS
/**
* Called to open further IO contexts when needed for demuxing.
*
* This can be set by the user application to perform security checks on
* the URLs before opening them.
* The function should behave like avio_open2(), AVFormatContext is provided
* as contextual information and to reach AVFormatContext.opaque.
*
* If NULL then some simple checks are used together with avio_open2().
*
* Must not be accessed directly from outside avformat.
* @See av_format_set_open_cb()
*
* Demuxing: Set by user.
*
* @deprecated Use io_open and io_close.
*/
attribute_deprecated
int (*open_cb)(struct AVFormatContext *s, AVIOContext **p, const char *url, int flags, const AVIOInterruptCB *int_cb, AVDictionary **options);
#endif
/**
* ',' separated list of allowed protocols.
* - encoding: unused
* - decoding: set by user
*/
char *protocol_whitelist;
/**
* A callback for opening new IO streams.
*
* Whenever a muxer or a demuxer needs to open an IO stream (typically from
* avformat_open_input() for demuxers, but for certain formats can happen at
* other times as well), it will call this callback to obtain an IO context.
*
* @param s the format context
* @param pb on success, the newly opened IO context should be returned here
* @param url the url to open
* @param flags a combination of AVIO_FLAG_*
* @param options a dictionary of additional options, with the same
* semantics as in avio_open2()
* @return 0 on success, a negative AVERROR code on failure
*
* @note Certain muxers and demuxers do nesting, i.e. they open one or more
* additional internal format contexts. Thus the AVFormatContext pointer
* passed to this callback may be different from the one facing the caller.
* It will, however, have the same 'opaque' field.
*/
int (*io_open)(struct AVFormatContext *s, AVIOContext **pb, const char *url,
int flags, AVDictionary **options);
/**
* A callback for closing the streams opened with AVFormatContext.io_open().
*/
void (*io_close)(struct AVFormatContext *s, AVIOContext *pb);
/**
* ',' separated list of disallowed protocols.
* - encoding: unused
* - decoding: set by user
*/
char *protocol_blacklist;
/**
* The maximum number of streams.
* - encoding: unused
* - decoding: set by user
*/
int max_streams;
/**
* Skip duration calcuation in estimate_timings_from_pts.
* - encoding: unused
* - decoding: set by user
*/
int skip_estimate_duration_from_pts;
/**
* Maximum number of packets that can be probed
* - encoding: unused
* - decoding: set by user
*/
int max_probe_packets;
} AVFormatContext;AVFormatContext是一个贯穿始终的数据结构，很多函数都要用到它作为参数
AVFormatContext -- 格式转换过程中实现输入和输出功能、保存相关数据的主要结构，描述了一个媒体文件或媒体流的构成和基本信息：
- nb_streams/streams ：AVStream结构指针数组, 包含了所有内嵌媒体流的描述，其内部有 AVInputFormat + AVOutputFormat 结构体，来表示输入输出的文件格式
- avformat_open_input：创建并初始化部分值，但其他一些值(如 mux_rate、key 等)需要手工设置初始值，否则可能出现异常
- avformat_alloc_output_context2：根据文件的输出格式、扩展名或文件名等分配合适的 AVFormatContext 结构
2. AVStream结构体
存储解码后每一个视频/音频流信息的结构体
typedef struct AVStream {
int index; /**< stream index in AVFormatContext */
/**
* Format-specific stream ID.
* decoding: set by libavformat
* encoding: set by the user, replaced by libavformat if left unset
*/
int id;
#if FF_API_LAVF_AVCTX
/**
* @deprecated use the codecpar struct instead
*/
attribute_deprecated
AVCodecContext *codec;
#endif
void *priv_data;
/**
* This is the fundamental unit of time (in seconds) in terms
* of which frame timestamps are represented.
*
* decoding: set by libavformat
* encoding: May be set by the caller before avformat_write_header() to
* provide a hint to the muxer about the desired timebase. In
* avformat_write_header(), the muxer will overwrite this field
* with the timebase that will actually be used for the timestamps
* written into the file (which may or may not be related to the
* user-provided one, depending on the format).
*/
AVRational time_base;
/**
* Decoding: pts of the first frame of the stream in presentation order, in stream time base.
* Only set this if you are absolutely 100% sure that the value you set
* it to really is the pts of the first frame.
* This may be undefined (AV_NOPTS_VALUE).
* @note The ASF header does NOT contain a correct start_time the ASF
* demuxer must NOT set this.
*/
int64_t start_time;
/**
* Decoding: duration of the stream, in stream time base.
* If a source file does not specify a duration, but does specify
* a bitrate, this value will be estimated from bitrate and file size.
*
* Encoding: May be set by the caller before avformat_write_header() to
* provide a hint to the muxer about the estimated duration.
*/
int64_t duration;
int64_t nb_frames; ///< number of frames in this stream if known or 0
int disposition; /**< AV_DISPOSITION_* bit field */
enum AVDiscard discard; ///< Selects which packets can be discarded at will and do not need to be demuxed.
/**
* sample aspect ratio (0 if unknown)
* - encoding: Set by user.
* - decoding: Set by libavformat.
*/
AVRational sample_aspect_ratio;
AVDictionary *metadata;
/**
* Average framerate
*
* - demuxing: May be set by libavformat when creating the stream or in
* avformat_find_stream_info().
* - muxing: May be set by the caller before avformat_write_header().
*/
AVRational avg_frame_rate;
/**
* For streams with AV_DISPOSITION_ATTACHED_PIC disposition, this packet
* will contain the attached picture.
*
* decoding: set by libavformat, must not be modified by the caller.
* encoding: unused
*/
AVPacket attached_pic;
/**
* An array of side data that applies to the whole stream (i.e. the
* container does not allow it to change between packets).
*
* There may be no overlap between the side data in this array and side data
* in the packets. I.e. a given side data is either exported by the muxer
* (demuxing) / set by the caller (muxing) in this array, then it never
* appears in the packets, or the side data is exported / sent through
* the packets (always in the first packet where the value becomes known or
* changes), then it does not appear in this array.
*
* - demuxing: Set by libavformat when the stream is created.
* - muxing: May be set by the caller before avformat_write_header().
*
* Freed by libavformat in avformat_free_context().
*
* @see av_format_inject_global_side_data()
*/
AVPacketSideData *side_data;
/**
* The number of elements in the AVStream.side_data array.
*/
int nb_side_data;
/**
* Flags indicating events happening on the stream, a combination of
* AVSTREAM_EVENT_FLAG_*.
*
* - demuxing: may be set by the demuxer in avformat_open_input(),
* avformat_find_stream_info() and av_read_frame(). Flags must be cleared
* by the user once the event has been handled.
* - muxing: may be set by the user after avformat_write_header(). to
* indicate a user-triggered event. The muxer will clear the flags for
* events it has handled in av_[interleaved]_write_frame().
*/
int event_flags;
/**
* - demuxing: the demuxer read new metadata from the file and updated
* AVStream.metadata accordingly
* - muxing: the user updated AVStream.metadata and wishes the muxer to write
* it into the file
*/
#define AVSTREAM_EVENT_FLAG_METADATA_UPDATED 0x0001
/**
* - demuxing: new packets for this stream were read from the file. This
* event is informational only and does not guarantee that new packets
* for this stream will necessarily be returned from av_read_frame().
*/
#define AVSTREAM_EVENT_FLAG_NEW_PACKETS (1 << 1)
/**
* Real base framerate of the stream.
* This is the lowest framerate with which all timestamps can be
* represented accurately (it is the least common multiple of all
* framerates in the stream). Note, this value is just a guess!
* For example, if the time base is 1/90000 and all frames have either
* approximately 3600 or 1800 timer ticks, then r_frame_rate will be 50/1.
*/
AVRational r_frame_rate;
#if FF_API_LAVF_FFSERVER
/**
* String containing pairs of key and values describing recommended encoder configuration.
* Pairs are separated by ','.
* Keys are separated from values by '='.
*
* @deprecated unused
*/
attribute_deprecated
char *recommended_encoder_configuration;
#endif
/**
* Codec parameters associated with this stream. Allocated and freed by
* libavformat in avformat_new_stream() and avformat_free_context()
* respectively.
*
* - demuxing: filled by libavformat on stream creation or in
* avformat_find_stream_info()
* - muxing: filled by the caller before avformat_write_header()
*/
AVCodecParameters *codecpar;
/*****************************************************************
* All fields below this line are not part of the public API. They
* may not be used outside of libavformat and can be changed and
* removed at will.
* Internal note: be aware that physically removing these fields
* will break ABI. Replace removed fields with dummy fields, and
* add new fields to AVStreamInternal.
*****************************************************************
*/
#if LIBAVFORMAT_VERSION_MAJOR < 59
// kept for ABI compatibility only, do not access in any way
void *unused;
#endif
int pts_wrap_bits; /**< number of bits in pts (used for wrapping control) */
// Timestamp generation support:
/**
* Timestamp corresponding to the last dts sync point.
*
* Initialized when AVCodecParserContext.dts_sync_point >= 0 and
* a DTS is received from the underlying container. Otherwise set to
* AV_NOPTS_VALUE by default.
*/
int64_t first_dts;
int64_t cur_dts;
int64_t last_IP_pts;
int last_IP_duration;
/**
* Number of packets to buffer for codec probing
*/
int probe_packets;
/**
* Number of frames that have been demuxed during avformat_find_stream_info()
*/
int codec_info_nb_frames;
/* av_read_frame() support */
enum AVStreamParseType need_parsing;
struct AVCodecParserContext *parser;
#if LIBAVFORMAT_VERSION_MAJOR < 59
// kept for ABI compatibility only, do not access in any way
void *unused7;
AVProbeData unused6;
int64_t unused5[16+1];
#endif
AVIndexEntry *index_entries; /**< Only used if the format does not
support seeking natively. */
int nb_index_entries;
unsigned int index_entries_allocated_size;
/**
* Stream Identifier
* This is the MPEG-TS stream identifier +1
* 0 means unknown
*/
int stream_identifier;
#if LIBAVFORMAT_VERSION_MAJOR < 59
// kept for ABI compatibility only, do not access in any way
int unused8;
int unused9;
int unused10;
#endif
/**
* An opaque field for libavformat internal usage.
* Must not be accessed in any way by callers.
*/
AVStreamInternal *internal;
} AVStream;
- int index：标识该视频/音频流
- AVCodecContext *codec：指向该视频/音频流的AVCodecContext（它们是一一对应的关系）
- AVRational time_base：时基。通过该值可以把PTS，DTS转化为真正的时间。FFMPEG其他结构体中也有这个字段，但是根据我的经验，只有AVStream中的time_base是可用的。PTS*time_base=真正的时间
- int64_t duration：该视频/音频流长度
- AVDictionary *metadata：元数据信息
- AVRational avg_frame_rate：帧率（注：对视频来说，这个挺重要的）
- AVPacket attached_pic：附带的图片。比如说一些MP3，AAC音频文件附带的专辑封面。
AVStream -- 描述一个媒体流，其大部分信息可通过 avformat_open_input 根据文件头信息确定，其他信息可通过 avformat_find_stream_info 获取，典型的有 视频流、中英文音频流、中英文字幕流(Subtitle)，可通过 av_new_stream、avformat_new_stream 等创建。
- index：在AVFormatContext中流的索引，其值自动生成(AVFormatContext::streams[index])
- nb_frames：流内的帧数目
- time_base：流的时间基准，是一个实数，该流中媒体数据的pts和dts都将以这个时间基准为粒度。通常，使用av_rescale/av_rescale_q可以实现不同时间基准的转换
- avformat_find_stream_info：获取必要的编解码器参数(如 AVMediaType、CodecID )，设置到 AVFormatContext::streams[i]::codec 中
- av_read_frame：从多媒体文件或多媒体流中读取媒体数据，获取的数据由 AVPacket 来存放
- av_seek_frame：改变媒体文件的读写指针来实现对媒体文件的随机访问，通常支持基于时间、文件偏移、帧号(AVSEEK_FLAG_FRAME)的随机访问方式
3.AVPacket结构体
typedef struct AVPacket {
/**
* A reference to the reference-counted buffer where the packet data is
* stored.
* May be NULL, then the packet data is not reference-counted.
*/
AVBufferRef *buf;
/**
* Presentation timestamp in AVStream->time_base units; the time at which
* the decompressed packet will be presented to the user.
* Can be AV_NOPTS_VALUE if it is not stored in the file.
* pts MUST be larger or equal to dts as presentation cannot happen before
* decompression, unless one wants to view hex dumps. Some formats misuse
* the terms dts and pts/cts to mean something different. Such timestamps
* must be converted to true pts/dts before they are stored in AVPacket.
*/
int64_t pts;
/**
* Decompression timestamp in AVStream->time_base units; the time at which
* the packet is decompressed.
* Can be AV_NOPTS_VALUE if it is not stored in the file.
*/
int64_t dts;
uint8_t *data;
int size;
int stream_index;
/**
* A combination of AV_PKT_FLAG values
*/
int flags;
/**
* Additional packet data that can be provided by the container.
* Packet can contain several types of side information.
*/
AVPacketSideData *side_data;
int side_data_elems;
/**
* Duration of this packet in AVStream->time_base units, 0 if unknown.
* Equals next_pts - this_pts in presentation order.
*/
int64_t duration;
int64_t pos; ///< byte position in stream, -1 if unknown
#if FF_API_CONVERGENCE_DURATION
/**
* @deprecated Same as the duration field, but as int64_t. This was required
* for Matroska subtitles, whose duration values could overflow when the
* duration field was still an int.
*/
attribute_deprecated
int64_t convergence_duration;
#endif
} AVPacket;AVPacket -- 暂存解码之前的媒体数据（一个音/视频帧、一个字幕包等）及附加信息（解码时间戳、显示时间戳、时长等)，主要用于建立缓冲区并装载数据。
- data/size/pos： 数据缓冲区指针、长度和媒体流中的字节偏移量
- flags：标志域的组合，1(AV_PKT_FLAG_KEY)表示该数据是一个关键帧, 2(AV_PKT_FLAG_CORRUPT)表示该数据已经损坏
- destruct：释放数据缓冲区的函数指针，其值可为 [av_destruct_packet]/av_destruct_packet_nofree, 会被 av_free_packet 调用
4.AVFrame结构体
typedef struct AVFrame {
#define AV_NUM_DATA_POINTERS 8
/**图像数据
* pointer to the picture/channel planes.
* This might be different from the first allocated byte
* - encoding: Set by user
* - decoding: set by AVCodecContext.get_buffer()
*/
uint8_t *data[AV_NUM_DATA_POINTERS];
/**
* Size, in bytes, of the data for each picture/channel plane.
*
* For audio, only linesize[0] may be set. For planar audio, each channel
* plane must be the same size.
*
* - encoding: Set by user
* - decoding: set by AVCodecContext.get_buffer()
*/
int linesize[AV_NUM_DATA_POINTERS];
/**
* pointers to the data planes/channels.
*
* For video, this should simply point to data[].
*
* For planar audio, each channel has a separate data pointer, and
* linesize[0] contains the size of each channel buffer.
* For packed audio, there is just one data pointer, and linesize[0]
* contains the total size of the buffer for all channels.
*
* Note: Both data and extended_data will always be set by get_buffer(),
* but for planar audio with more channels that can fit in data,
* extended_data must be used by the decoder in order to access all
* channels.
*
* encoding: unused
* decoding: set by AVCodecContext.get_buffer()
*/
uint8_t **extended_data;
/**宽高
* width and height of the video frame
* - encoding: unused
* - decoding: Read by user.
*/
int width, height;
/**
* number of audio samples (per channel) described by this frame
* - encoding: Set by user
* - decoding: Set by libavcodec
*/
int nb_samples;
/**
* format of the frame, -1 if unknown or unset
* Values correspond to enum AVPixelFormat for video frames,
* enum AVSampleFormat for audio)
* - encoding: unused
* - decoding: Read by user.
*/
int format;
/**是否是关键帧
* 1 -> keyframe, 0-> not
* - encoding: Set by libavcodec.
* - decoding: Set by libavcodec.
*/
int key_frame;
/**帧类型（I,B,P）
* Picture type of the frame, see ?_TYPE below.
* - encoding: Set by libavcodec. for coded_picture (and set by user for input).
* - decoding: Set by libavcodec.
*/
enum AVPictureType pict_type;
/**
* pointer to the first allocated byte of the picture. Can be used in get_buffer/release_buffer.
* This isn't used by libavcodec unless the default get/release_buffer() is used.
* - encoding:
* - decoding:
*/
uint8_t *base[AV_NUM_DATA_POINTERS];
/**
* sample aspect ratio for the video frame, 0/1 if unknown/unspecified
* - encoding: unused
* - decoding: Read by user.
*/
AVRational sample_aspect_ratio;
/**
* presentation timestamp in time_base units (time when frame should be shown to user)
* If AV_NOPTS_VALUE then frame_rate = 1/time_base will be assumed.
* - encoding: MUST be set by user.
* - decoding: Set by libavcodec.
*/
int64_t pts;
/**
* reordered pts from the last AVPacket that has been input into the decoder
* - encoding: unused
* - decoding: Read by user.
*/
int64_t pkt_pts;
/**
* dts from the last AVPacket that has been input into the decoder
* - encoding: unused
* - decoding: Read by user.
*/
int64_t pkt_dts;
/**
* picture number in bitstream order
* - encoding: set by
* - decoding: Set by libavcodec.
*/
int coded_picture_number;
/**
* picture number in display order
* - encoding: set by
* - decoding: Set by libavcodec.
*/
int display_picture_number;
/**
* quality (between 1 (good) and FF_LAMBDA_MAX (bad))
* - encoding: Set by libavcodec. for coded_picture (and set by user for input).
* - decoding: Set by libavcodec.
*/
int quality;
/**
* is this picture used as reference
* The values for this are the same as the MpegEncContext.picture_structure
* variable, that is 1->top field, 2->bottom field, 3->frame/both fields.
* Set to 4 for delayed, non-reference frames.
* - encoding: unused
* - decoding: Set by libavcodec. (before get_buffer() call)).
*/
int reference;
/**QP表
* QP table
* - encoding: unused
* - decoding: Set by libavcodec.
*/
int8_t *qscale_table;
/**
* QP store stride
* - encoding: unused
* - decoding: Set by libavcodec.
*/
int qstride;
/**
*
*/
int qscale_type;
/**跳过宏块表
* mbskip_table[mb]>=1 if MB didn't change
* stride= mb_width = (width+15)>>4
* - encoding: unused
* - decoding: Set by libavcodec.
*/
uint8_t *mbskip_table;
/**运动矢量表
* motion vector table
* @code
* example:
* int mv_sample_log2= 4 - motion_subsample_log2;
* int mb_width= (width+15)>>4;
* int mv_stride= (mb_width << mv_sample_log2) + 1;
* motion_val[direction][x + y*mv_stride][0->mv_x, 1->mv_y];
* @endcode
* - encoding: Set by user.
* - decoding: Set by libavcodec.
*/
int16_t (*motion_val[2])[2];
/**宏块类型表
* macroblock type table
* mb_type_base + mb_width + 2
* - encoding: Set by user.
* - decoding: Set by libavcodec.
*/
uint32_t *mb_type;
/**DCT系数
* DCT coefficients
* - encoding: unused
* - decoding: Set by libavcodec.
*/
short *dct_coeff;
/**参考帧列表
* motion reference frame index
* the order in which these are stored can depend on the codec.
* - encoding: Set by user.
* - decoding: Set by libavcodec.
*/
int8_t *ref_index[2];
/**
* for some private data of the user
* - encoding: unused
* - decoding: Set by user.
*/
void *opaque;
/**
* error
* - encoding: Set by libavcodec. if flags&CODEC_FLAG_PSNR.
* - decoding: unused
*/
uint64_t error[AV_NUM_DATA_POINTERS];
/**
* type of the buffer (to keep track of who has to deallocate data[*])
* - encoding: Set by the one who allocates it.
* - decoding: Set by the one who allocates it.
* Note: User allocated (direct rendering) & internal buffers cannot coexist currently.
*/
int type;
/**
* When decoding, this signals how much the picture must be delayed.
* extra_delay = repeat_pict / (2*fps)
* - encoding: unused
* - decoding: Set by libavcodec.
*/
int repeat_pict;
/**
* The content of the picture is interlaced.
* - encoding: Set by user.
* - decoding: Set by libavcodec. (default 0)
*/
int interlaced_frame;
/**
* If the content is interlaced, is top field displayed first.
* - encoding: Set by user.
* - decoding: Set by libavcodec.
*/
int top_field_first;
/**
* Tell user application that palette has changed from previous frame.
* - encoding: ??? (no palette-enabled encoder yet)
* - decoding: Set by libavcodec. (default 0).
*/
int palette_has_changed;
/**
* codec suggestion on buffer type if != 0
* - encoding: unused
* - decoding: Set by libavcodec. (before get_buffer() call)).
*/
int buffer_hints;
/**
* Pan scan.
* - encoding: Set by user.
* - decoding: Set by libavcodec.
*/
AVPanScan *pan_scan;
/**
* reordered opaque 64bit (generally an integer or a double precision float
* PTS but can be anything).
* The user sets AVCodecContext.reordered_opaque to represent the input at
* that time,
* the decoder reorders values as needed and sets AVFrame.reordered_opaque
* to exactly one of the values provided by the user through AVCodecContext.reordered_opaque
* @deprecated in favor of pkt_pts
* - encoding: unused
* - decoding: Read by user.
*/
int64_t reordered_opaque;
/**
* hardware accelerator private data (FFmpeg-allocated)
* - encoding: unused
* - decoding: Set by libavcodec
*/
void *hwaccel_picture_private;
/**
* the AVCodecContext which ff_thread_get_buffer() was last called on
* - encoding: Set by libavcodec.
* - decoding: Set by libavcodec.
*/
struct AVCodecContext *owner;
/**
* used by multithreading to store frame-specific info
* - encoding: Set by libavcodec.
* - decoding: Set by libavcodec.
*/
void *thread_opaque;
/**
* log2 of the size of the block which a single vector in motion_val represents:
* (4->16x16, 3->8x8, 2-> 4x4, 1-> 2x2)
* - encoding: unused
* - decoding: Set by libavcodec.
*/
uint8_t motion_subsample_log2;
/**（音频）采样率
* Sample rate of the audio data.
*
* - encoding: unused
* - decoding: read by user
*/
int sample_rate;
/**
* Channel layout of the audio data.
*
* - encoding: unused
* - decoding: read by user.
*/
uint64_t channel_layout;
/**
* frame timestamp estimated using various heuristics, in stream time base
* Code outside libavcodec should access this field using:
* av_frame_get_best_effort_timestamp(frame)
* - encoding: unused
* - decoding: set by libavcodec, read by user.
*/
int64_t best_effort_timestamp;
/**
* reordered pos from the last AVPacket that has been input into the decoder
* Code outside libavcodec should access this field using:
* av_frame_get_pkt_pos(frame)
* - encoding: unused
* - decoding: Read by user.
*/
int64_t pkt_pos;
/**
* duration of the corresponding packet, expressed in
* AVStream->time_base units, 0 if unknown.
* Code outside libavcodec should access this field using:
* av_frame_get_pkt_duration(frame)
* - encoding: unused
* - decoding: Read by user.
*/
int64_t pkt_duration;
/**
* metadata.
* Code outside libavcodec should access this field using:
* av_frame_get_metadata(frame)
* - encoding: Set by user.
* - decoding: Set by libavcodec.
*/
AVDictionary *metadata;
/**
* decode error flags of the frame, set to a combination of
* FF_DECODE_ERROR_xxx flags if the decoder produced a frame, but there
* were errors during the decoding.
* Code outside libavcodec should access this field using:
* av_frame_get_decode_error_flags(frame)
* - encoding: unused
* - decoding: set by libavcodec, read by user.
*/
int decode_error_flags;
#define FF_DECODE_ERROR_INVALID_BITSTREAM 1
#define FF_DECODE_ERROR_MISSING_REFERENCE 2
/**
* number of audio channels, only used for audio.
* Code outside libavcodec should access this field using:
* av_frame_get_channels(frame)
* - encoding: unused
* - decoding: Read by user.
*/
int64_t channels;
} AVFrame;（1）作用
AVFrame结构体一般用于存储原始数据（即非压缩数据，例如对视频来说是YUV，RGB，对音频来说是PCM），此外还包含了一些相关的信息。比如说，解码的时候存储了宏块类型表，QP表，运动矢量表等数据。编码的时候也存储了相关的数据。
（2）data[]
对于packed格式的数据（例如RGB24），会存到data[0]里面。
对于planar格式的数据（例如YUV420P），则会分开成data[0]，data[1]，data[2]...（YUV420P中data[0]存Y，data[1]存U，data[2]存V）
（3）pict_type
包含以下类型：
enum AVPictureType {
AV_PICTURE_TYPE_NONE = 0, ///< Undefined
AV_PICTURE_TYPE_I, ///< Intra
AV_PICTURE_TYPE_P, ///< Predicted
AV_PICTURE_TYPE_B, ///< Bi-dir predicted
AV_PICTURE_TYPE_S, ///< S(GMC)-VOP MPEG4
AV_PICTURE_TYPE_SI, ///< Switching Intra
AV_PICTURE_TYPE_SP, ///< Switching Predicted
AV_PICTURE_TYPE_BI, ///< BI type
};（4）sample_aspect_ratio
宽高比是一个分数，FFMPEG中用AVRational表达分数：
/**
* rational number numerator/denominator
*/
typedef struct AVRational{
int num; ///< numerator
int den; ///< denominator
} AVRational;（5）qscale_table
QP表指向一块内存，里面存储的是每个宏块的QP值。宏块的标号是从左往右，一行一行的来的。每个宏块对应1个QP。
qscale_table[0]就是第1行第1列宏块的QP值；qscale_table[1]就是第1行第2列宏块的QP值；qscale_table[2]就是第1行第3列宏块的QP值。以此类推...
宏块的个数用下式计算：
注：宏块大小是16x16的。
每行宏块数：int mb_stride = pCodecCtx->width/16+1 宏块的总数：int mb_sum = ((pCodecCtx->height+15)>>4)*(pCodecCtx->width/16+1)
5.AVCodec结构体
typedef struct AVCodec {
/**
* Name of the codec implementation.
* The name is globally unique among encoders and among decoders (but an
* encoder and a decoder can share the same name).
* This is the primary way to find a codec from the user perspective.
*/
const char *name;
/**
* Descriptive name for the codec, meant to be more human readable than name.
* You should use the NULL_IF_CONFIG_SMALL() macro to define it.
*/
const char *long_name;
enum AVMediaType type;
enum CodecID id;
/**
* Codec capabilities.
* see CODEC_CAP_*
*/
int capabilities;
const AVRational *supported_framerates; ///< array of supported framerates, or NULL if any, array is terminated by {0,0}
const enum PixelFormat *pix_fmts; ///< array of supported pixel formats, or NULL if unknown, array is terminated by -1
const int *supported_samplerates; ///< array of supported audio samplerates, or NULL if unknown, array is terminated by 0
const enum AVSampleFormat *sample_fmts; ///< array of supported sample formats, or NULL if unknown, array is terminated by -1
const uint64_t *channel_layouts; ///< array of support channel layouts, or NULL if unknown. array is terminated by 0
uint8_t max_lowres; ///< maximum value for lowres supported by the decoder
const AVClass *priv_class; ///< AVClass for the private context
const AVProfile *profiles; ///< array of recognized profiles, or NULL if unknown, array is terminated by {FF_PROFILE_UNKNOWN}
/*****************************************************************
* No fields below this line are part of the public API. They
* may not be used outside of libavcodec and can be changed and
* removed at will.
* New public fields should be added right above.
*****************************************************************
*/
int priv_data_size;
struct AVCodec *next;
/**
* @name Frame-level threading support functions
* @{
*/
/**
* If defined, called on thread contexts when they are created.
* If the codec allocates writable tables in init(), re-allocate them here.
* priv_data will be set to a copy of the original.
*/
int (*init_thread_copy)(AVCodecContext *);
/**
* Copy necessary context variables from a previous thread context to the current one.
* If not defined, the next thread will start automatically; otherwise, the codec
* must call ff_thread_finish_setup().
*
* dst and src will (rarely) point to the same context, in which case memcpy should be skipped.
*/
int (*update_thread_context)(AVCodecContext *dst, const AVCodecContext *src);
/** @} */
/**
* Private codec-specific defaults.
*/
const AVCodecDefault *defaults;
/**
* Initialize codec static data, called from avcodec_register().
*/
void (*init_static_data)(struct AVCodec *codec);
int (*init)(AVCodecContext *);
int (*encode)(AVCodecContext *, uint8_t *buf, int buf_size, void *data);
/**
* Encode data to an AVPacket.
*
* @param avctx codec context
* @param avpkt output AVPacket (may contain a user-provided buffer)
* @param[in] frame AVFrame containing the raw data to be encoded
* @param[out] got_packet_ptr encoder sets to 0 or 1 to indicate that a
* non-empty packet was returned in avpkt.
* @return 0 on success, negative error code on failure
*/
int (*encode2)(AVCodecContext *avctx, AVPacket *avpkt, const AVFrame *frame,
int *got_packet_ptr);
int (*decode)(AVCodecContext *, void *outdata, int *outdata_size, AVPacket *avpkt);
int (*close)(AVCodecContext *);
/**
* Flush buffers.
* Will be called when seeking
*/
void (*flush)(AVCodecContext *);
} AVCodec;