参考链接

• FFMPEG结构体分析：AVStream_雷霄骅的博客-CSDN博客_avstream

AVStream

• AVStream是是存储每一个视频/音频流信息的结构体
• 结构体的定义位于avformat.h
• 重要参数介绍
  • 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。

代码

/*** Stream structure. //流结构* New fields can be added to the end with minor version bumps. //可以将新字段添加到末尾，并带有较小的版本颠簸* Removal, reordering and changes to existing fields require a major //移除、重新排序和更改现有字段需要专业版本颠簸* version bump.* sizeof(AVStream) must not be used outside libav*. //sizeof(AVStream) 不得在 libav* 之外使用*/
typedef struct AVStream {
#if FF_API_AVSTREAM_CLASS/*** A class for @ref avoptions. Set on stream creation.*/const AVClass *av_class;
#endifint 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;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/*** Stream disposition - a combination of AV_DISPOSITION_* flags.* - demuxing: set by libavformat when creating the stream or in*             avformat_find_stream_info().* - muxing: may be set by the caller before avformat_write_header().*/int disposition;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;/*** 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;/*** Number of bits in timestamps. Used for wrapping control.** - demuxing: set by libavformat* - muxing: set by libavformat**/int pts_wrap_bits;
} AVStream;