对于视频来说，linesize是每行图像的大小(字节数)。注意有对齐要求。
对于音频来说，linesize是每个plane的大小(字节数)。音频只使用linesize[0]。对于planar音频来说，每个plane的大小必须一样。
linesize可能会因性能上的考虑而填充一些额外的数据，因此linesize可能比实际对应的音视频数据尺寸要大。
extended_data
/** * 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 should always be set in a valid frame, * but for planar audio with more channels that can fit in data, * extended_data must be used in order to access all channels. */ uint8_t **extended_data;????extended_data是干啥的????
对于视频来说，直接指向data[]成员。
对于音频来说，packet格式音频只有一个plane，一个音频帧中各个声道的采样点交织存储在此plane中；planar格式音频每个声道一个plane。在多声道planar格式音频中，必须使用extended_data才能访问所有声道，什么意思？
在有效的视频/音频frame中，data和extended_data两个成员都必须设置有效值。
width, height
/** * @name Video dimensions * Video frames only. The coded dimensions (in pixels) of the video frame, * i.e. the size of the rectangle that contains some well-defined values. * * @note The part of the frame intended for display/presentation is further * restricted by the @ref cropping "Cropping rectangle". * @{ */ int width, height;视频帧宽和高(像素)。
nb_samples
/** * number of audio samples (per channel) described by this frame */ int nb_samples;音频帧中单个声道中包含的采样点数。
format
/** * format of the frame, -1 if unknown or unset * Values correspond to enum AVPixelFormat for video frames, * enum AVSampleFormat for audio) */ int format;帧格式。如果是未知格式或未设置，则值为-1。
对于视频帧，此值对应于“enum AVPixelFormat”结构：
对于音频帧，此值对应于“enum AVSampleFormat”格式：
enum AVSampleFormat { AV_SAMPLE_FMT_NONE = -1, AV_SAMPLE_FMT_U8, ///< unsigned 8 bits AV_SAMPLE_FMT_S16, ///< signed 16 bits AV_SAMPLE_FMT_S32, ///< signed 32 bits AV_SAMPLE_FMT_FLT, ///< float AV_SAMPLE_FMT_DBL, ///< double AV_SAMPLE_FMT_U8P, ///< unsigned 8 bits, planar AV_SAMPLE_FMT_S16P, ///< signed 16 bits, planar AV_SAMPLE_FMT_S32P, ///< signed 32 bits, planar AV_SAMPLE_FMT_FLTP, ///< float, planar AV_SAMPLE_FMT_DBLP, ///< double, planar AV_SAMPLE_FMT_S64, ///< signed 64 bits AV_SAMPLE_FMT_S64P, ///< signed 64 bits, planar AV_SAMPLE_FMT_NB ///< Number of sample formats. DO NOT USE if linking dynamically };key_frame
/** * 1 -> keyframe, 0-> not */ int key_frame;视频帧是否是关键帧的标识，1->关键帧，0->非关键帧。
pict_type
/** * Picture type of the frame. */ enum AVPictureType pict_type;视频帧类型(I、B、P等)。如下：
/** * @} * @} * @defgroup lavu_picture Image related * * AVPicture types, pixel formats and basic image planes manipulation. * * @{ */ 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 MPEG-4 AV_PICTURE_TYPE_SI, ///< Switching Intra AV_PICTURE_TYPE_SP, ///< Switching Predicted AV_PICTURE_TYPE_BI, ///< BI type };sample_aspect_ratio
/** * Sample aspect ratio for the video frame, 0/1 if unknown/unspecified. */ AVRational sample_aspect_ratio;视频帧的宽高比。
pts
/** * Presentation timestamp in time_base units (time when frame should be shown to user). */ int64_t pts;显示时间戳。单位是time_base。
pkt_pts
#if FF_API_PKT_PTS /** * PTS copied from the AVPacket that was decoded to produce this frame. * @deprecated use the pts field instead */ attribute_deprecated int64_t pkt_pts; #endif此frame对应的packet中的显示时间戳。是从对应packet(解码生成此frame)中拷贝PTS得到此值。