FFMPEG结构体分析：AVFrame(解码后的数据)

https://blog.csdn.net/jxcr1984/article/details/52766524

本文转自: http://blog.csdn.net/leixiaohua1020/article/details/14214577

/*
*雷霄骅
*[email protected]
*中国传媒大学/数字电视技术
*/
/**
* Audio Video Frame.
* New fields can be added to the end of AVFRAME with minor version
* bumps. Similarly fields that are marked as to be only accessed by
* av_opt_ptr() can be reordered. This allows 2 forks to add fields
* without breaking compatibility with each other.
* Removal, reordering and changes in the remaining cases require
* a major version bump.
* sizeof(AVFrame) must not be used outside libavcodec.
*/
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;

AVFrame结构体为解码后的数据，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，对于音频来说就是PCM），此外还包括一些相关的数据。

如：解码的时候存储了宏块类型表，QP表，运行矢量表等数据。编码的时候也存储了相关的数据。因此在使用FFMPEG进行码流分析的时候，AVFrame是一个很重要的结构体。

uint8_t *data[AV_NUM_DATA_POINTERS]: 解码后原始数据

int linesize[AV_NUM_DATA_PONITERS]: data中"一行"数据的大小。注：未必就是图像的宽，一般大于图像的宽

int width, height: 视频帧宽和高(1920*1080)

int nb_samples: 音频的一个AVFrame中可能包含多个音频帧，在此标记包含了几个

int format: 解码后原始数据型(YUV420, YUV422, RGB24...)

int key_frame: 是否为关键帧

enum AVPictureType pict_type: 帧类型(I,B,P...)

AVRational sample_aspect_ratio: 宽高比(16:9, 4:3...)

int64_t pts: 显示时间戳

int coded_picture_number: 编码帧序号

int display_picture_number: 显示帧序号

int8_t *qscale_table: QP表

uint8_t *mbskip_table: 跳过宏块表

int16_t (*motion_val[2])[2]: 运行矢量表

uint32_t *mb_type: 宏块类型表

short *dct_coeff: DCT系数

int8_t *ref_index[2]: 运动估计参考帧列表

int interlaced_frame: 是否是隔行扫描

uint8_t motion_subsample_log2: 一个宏块中的运行矢量采样个数，取log的