ffmpeg AVPacket、AVPicture、AVFrame

一、AVPacket

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/**

• AVPacket 作为解码器的输入 或 编码器的输出。
• 当作为解码器的输入时，它由demuxer生成，然后传递给解码器
• 当作为编码器的输出时，由编码器生成，然后传递给muxer
• 在视频中，AVPacket 只能包含不大于1帧的内容，而视频的1帧可能要包含在多个AVPacket中，AVPacket < AVFrame
• AVPacket 是ffmpeg中少数的几个公共ABI，它只能被libavcodec和libformat在栈上分配
• The side data is always allocated with av_malloc() and is freed in
• av_free_packet().
  */

typedef struct AVPacket {  
/** 
     * packet的内存空间来自于一个叫做“引用计数缓冲区”的地方，这个指针就指向一块引用计数缓冲区 
     */  
    AVBufferRef *buf;  
/** 
     * 显示时间戳 单位是 AVStream->time_base units 
     */  
    int64_t pts;  
/** 
     * 解压时间戳，在这个时刻该包需要被解码 
     */  
    int64_t dts;  
    uint8_t *data;  
int   size;  
int   stream_index;  
/** 
     * A combination of AV_PKT_FLAG values 
     */  
int   flags;  
/** 
     * 存放额外的包信息 
     */  
struct {  
        uint8_t *data;  
int      size;  
enum AVPacketSideDataType type;  
    } *side_data;  
int side_data_elems;  
/** 
     * 这个包的时间长度 in AVStream->time_base units, 设置0 表示未知. 
     * duration = next_pts - this_pts i. 
     */  
int   duration;  
    int64_t pos;                            ///< 在数据流中的字节偏移量, -1 if unknown  
    int64_t convergence_duration;  
} AVPacket;  

二、AVPicture

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typedef struct AVPicture {  
    uint8_t *data[AV_NUM_DATA_POINTERS];    ///< pointers to the image data planes  
int linesize[AV_NUM_DATA_POINTERS];     ///< number of bytes per line  
}  

三、AVFrame

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/**

• AVFrame表示解码过后的一个数据帧
• AVFrame 通过使用 av_frame_alloc()来创建. 这个函数只是创建了AVFrame结构本身，在结构
• 中定义的指向其他内存块的缓冲区指针要用其他方法来分配
• 使用 av_frame_free()来释放AVFrame.

 */  
typedef struct AVFrame {  
#define AV_NUM_DATA_POINTERS 8  
/** 
     * pointer to the picture/channel planes. 
     */  
    uint8_t *data[AV_NUM_DATA_POINTERS];  
/** 
     * For video, size in bytes of each picture line. 
     * For audio, size in bytes of each plane. 
     */  
int linesize[AV_NUM_DATA_POINTERS];  
/** 
     * pointers to the data planes/channels. 
     */  
    uint8_t **extended_data;  
/** 
     * width and height of the video frame 
     */  
int width, height;  
/** 
     * number of audio samples (per channel) described by this frame 
     */  
int nb_samples;  
/** 
     * format of the frame, -1 if unknown or unset 
     */  
int format;  
/** 
     * 1 -> keyframe, 0-> not 
     */  
int key_frame;  
/** 
     * Picture type of the frame. 
     */  
enum AVPictureType pict_type;  
/** 
     * Sample aspect ratio for the video frame, 0/1 if unknown/unspecified. 
     */  
    AVRational sample_aspect_ratio;  
/** 
     * Presentation timestamp in time_base units (time when frame should be shown to user). 
     */  
    int64_t pts;  
/** 
     * PTS copied from the AVPacket that was decoded to produce this frame. 
     */  
    int64_t pkt_pts;  
/** 
     * DTS copied from the AVPacket that triggered returning this frame. (if frame threading isnt used) 
     * This is also the Presentation time of this AVFrame calculated from 
     * only AVPacket.dts values without pts values. 
     */  
    int64_t pkt_dts;  
/** 
     * picture number in bitstream order 
     */  
int coded_picture_number;  
/** 
     * picture number in display order 
     */  
int display_picture_number;  
/** 
     * quality (between 1 (good) and FF_LAMBDA_MAX (bad)) 
     */  
int quality;  
/** 
     * for some private data of the user 
     */  
void *opaque;  
/** 
     * error 
     */  
    uint64_t error[AV_NUM_DATA_POINTERS];  
/** 
     * When decoding, this signals how much the picture must be delayed. 
     * extra_delay = repeat_pict / (2*fps) 
     */  
int repeat_pict;  
/** 
     * The content of the picture is interlaced. 
     */  
int interlaced_frame;  
/** 
     * If the content is interlaced, is top field displayed first. 
     */  
int top_field_first;  
/** 
     * Tell user application that palette has changed from previous frame. 
     */  
int palette_has_changed;  
/** 
     * Sample rate of the audio data. 
     */  
int sample_rate;  
/** 
     * Channel layout of the audio data. 
     */  
    uint64_t channel_layout;  
/** 
     * 指向这个帧要用到的AVBuffer中的数据缓冲区. 
     * 
     * 一般每个图像位面（就时data[0],data[1] data[2]）只有一个指向AVBuffer的缓冲区, so for video this array 
     * always contains all the references. For planar audio with more than 
     * AV_NUM_DATA_POINTERS channels, there may be more buffers than can fit in 
     * this array. Then the extra AVBufferRef pointers are stored in the 
     * extended_buf array. 
     */  
    AVBufferRef *buf[AV_NUM_DATA_POINTERS];  
/** 
     * For planar audio which requires more than AV_NUM_DATA_POINTERS 
     * AVBufferRef pointers, this array will hold all the references which 
     * cannot fit into AVFrame.buf. 
     */  
    AVBufferRef **extended_buf;  
/** 
     * Number of elements in extended_buf. 
     */  
int        nb_extended_buf;  
    AVFrameSideData **side_data;  
int            nb_side_data;  
/** 
 * 可能因为解码错误，数据帧Frame会成为无效的帧，下面的结构就是当数据帧无效时使用的 
 */  
#define AV_FRAME_FLAG_CORRUPT       (1 << 0)  
/** 
     * Frame flags, a combination of AV_FRAME_FLAG_* 
     */  
int flags;  
    int64_t best_effort_timestamp;  
    int64_t pkt_pos;  
    int64_t pkt_duration;  
    AVDictionary *metadata;  
int decode_error_flags;  
#define FF_DECODE_ERROR_INVALID_BITSTREAM   1  
#define FF_DECODE_ERROR_MISSING_REFERENCE   2  
int channels;  
int pkt_size;  
enum AVColorSpace colorspace;  
enum AVColorRange color_range;  
/** 
     * Not to be accessed directly from outside libavutil 
     */  
    AVBufferRef *qp_table_buf;  
} AVFrame;