pkt_dts
/** * DTS copied from the AVPacket that triggered returning this frame. (if frame threading isn't used) * This is also the Presentation time of this AVFrame calculated from * only AVPacket.dts values without pts values. */ int64_t pkt_dts;此frame对应的packet中的解码时间戳。是从对应packet(解码生成此frame)中拷贝DTS得到此值。
如果对应的packet中只有dts而未设置pts，则此值也是此frame的pts。
coded_picture_number
/** * picture number in bitstream order */ int coded_picture_number;在编码流中当前图像的序号。
display_picture_number
/** * picture number in display order */ int display_picture_number;在显示序列中当前图像的序号。
interlaced_frame
/** * The content of the picture is interlaced. */ int interlaced_frame;图像逐行/隔行模式标识。
sample_rate
/** * Sample rate of the audio data. */ int sample_rate;音频采样率。
channel_layout
/** * Channel layout of the audio data. */ uint64_t channel_layout;音频声道布局。每bit代表一个特定的声道，参考channel_layout.h中的定义，一目了然：
/** * @defgroup channel_masks Audio channel masks * * A channel layout is a 64-bits integer with a bit set for every channel. * The number of bits set must be equal to the number of channels. * The value 0 means that the channel layout is not known. * @note this data structure is not powerful enough to handle channels * combinations that have the same channel multiple times, such as * dual-mono. * * @{ */ #define AV_CH_FRONT_LEFT 0x00000001 #define AV_CH_FRONT_RIGHT 0x00000002 #define AV_CH_FRONT_CENTER 0x00000004 #define AV_CH_LOW_FREQUENCY 0x00000008 ...... /** * @} * @defgroup channel_mask_c Audio channel layouts * @{ * */ #define AV_CH_LAYOUT_MONO (AV_CH_FRONT_CENTER) #define AV_CH_LAYOUT_STEREO (AV_CH_FRONT_LEFT|AV_CH_FRONT_RIGHT) #define AV_CH_LAYOUT_2POINT1 (AV_CH_LAYOUT_STEREO|AV_CH_LOW_FREQUENCY)buf
/** * AVBuffer references backing the data for this frame. If all elements of * this array are NULL, then this frame is not reference counted. This array * must be filled contiguously -- if buf[i] is non-NULL then buf[j] must * also be non-NULL for all j < i. * * There may be at most one AVBuffer per data plane, 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];此帧的数据可以由AVBufferRef管理，AVBufferRef提供AVBuffer引用机制。这里涉及到缓冲区引用计数概念：
AVBuffer是FFmpeg中很常用的一种缓冲区，缓冲区使用引用计数(reference-counted)机制。
AVBufferRef则对AVBuffer缓冲区提供了一层封装，最主要的是作引用计数处理，实现了一种安全机制。用户不应直接访问AVBuffer，应通过AVBufferRef来访问AVBuffer，以保证安全。
FFmpeg中很多基础的数据结构都包含了AVBufferRef成员，来间接使用AVBuffer缓冲区。
相关内容参考“FFmpeg数据结构AVBuffer”
????帧的数据缓冲区AVBuffer就是前面的data成员，用户不应直接使用data成员，应通过buf成员间接使用data成员。那extended_data又是做什么的呢????
如果buf[]的所有元素都为NULL，则此帧不会被引用计数。必须连续填充buf[] - 如果buf[i]为非NULL，则对于所有j<i，buf[j]也必须为非NULL。
每个plane最多可以有一个AVBuffer，一个AVBufferRef指针指向一个AVBuffer，一个AVBuffer引用指的就是一个AVBufferRef指针。
对于视频来说，buf[]包含所有AVBufferRef指针。对于具有多于AV_NUM_DATA_POINTERS个声道的planar音频来说，可能buf[]存不下所有的AVBbufferRef指针，多出的AVBufferRef指针存储在extended_buf数组中。
extended_buf&nb_extended_buf
/** * 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. * * Note that this is different from AVFrame.extended_data, which always * contains all the pointers. This array only contains the extra pointers, * which cannot fit into AVFrame.buf. * * This array is always allocated using av_malloc() by whoever constructs * the frame. It is freed in av_frame_unref(). */ AVBufferRef **extended_buf; /** * Number of elements in extended_buf. */ int nb_extended_buf;