ffmpeg 基本数据结构和对象（一）： AVPacket、AVPicture、AVFrame

来源：http://blog.csdn.net/chance_yin/article/details/16817957

一、AVPacket

/**
* 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

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

/**
* 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;

巴特西

ffmpeg 基本数据结构和对象（一）： AVPacket、AVPicture、AVFrame

最新文章

热门文章