标签：AVpacket audio int frame 源码 av AVFrame data

FFmpeg有两个存储帧数据的结构体，其中AVPacket是解封装后保存压缩数据包，AVFrame是解码后保存音视频帧。

AVPacket结构体以前放在avcodec.h头文件中，在FFmpeg4.4以后放在单独packet.h头文件。官方对AVPacket的说明如下：

/**
 * This structure stores compressed data. It is typically exported by demuxers
 * and then passed as input to decoders, or received as output from encoders and
 * then passed to muxers.
 *
 * For video, it should typically contain one compressed frame. For audio it may
 * contain several compressed frames. Encoders are allowed to output empty
 * packets, with no compressed data, containing only side data
 * (e.g. to update some stream parameters at the end of encoding).
 *
 */

AVPacket结构体定义如下：

typedef struct AVPacket {

    AVBufferRef *buf;
    // 显示时间戳，单位为AVStream->time_base
    int64_t pts;
    // 解码时间戳，单位为AVStream->time_base
    int64_t dts;
    // 音视频数据
    uint8_t *data;
    // 数据包大小
    int   size;
    // 码流索引下标
    int   stream_index;
    // 帧类型
    int   flags;
    // 额外数据
    AVPacketSideData *side_data;
    int side_data_elems;
    // 帧显示时长，单位为AVStream->time_base
    int64_t duration;
    // 数据包所在码流的position
    int64_t pos;

} AVPacket;

AVPacket的分配与释放有对应的API，需要注意的是释放所传的参数为AVPacket指针的地址。API与示例如下：

API:
AVPacket *av_packet_alloc(void);

void av_packet_free(AVPacket **pkt);

demo:
AVPacket *pkt = av_packet_alloc();

av_packet_free(&pkt);

AVFrame结构体位于frame.h头文件，用于存储解码后的音视频帧数据，使用av_frame_alloc进行分配，使用av_frame_free进行释放，AVFrame分配一次，多次复用，使用av_frame_unref可以去引用。官方关于AVFrame的描述如下：

/**
 * This structure describes decoded (raw) audio or video data.
 *
 * AVFrame must be allocated using av_frame_alloc(). Note that this only
 * allocates the AVFrame itself, the buffers for the data must be managed
 * through other means (see below).
 * AVFrame must be freed with av_frame_free().
 *
 * AVFrame is typically allocated once and then reused multiple times to hold
 * different data (e.g. a single AVFrame to hold frames received from a
 * decoder). In such a case, av_frame_unref() will free any references held by
 * the frame and reset it to its original clean state before it
 * is reused again.
 */

AVFrame是解码后用于存储音视频帧，包括：data数组、width、height、pts、pkt_dts、pkt_size、pkt_duration、pkt_pos等信息，我们在判断是否为关键帧时，用key_frame参数进行判断。结构体的定义如下：

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.
     *
     * For audio, only linesize[0] may be set. For planar audio, each channel
     * plane must be the same size.
     *
     * For video the linesizes should be multiples of the CPUs alignment
     * preference, this is 16 or 32 for modern desktop CPUs.
     * Some code requires such alignment other code can be slower without
     * correct alignment, for yet other it makes no difference.
     */
    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.
     */
    uint8_t **extended_data;

    /**
     * @name Video dimensions
     */
    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
     * Values correspond to enum AVPixelFormat for video frames,
     * enum AVSampleFormat for audio)
     */
    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.
     */
    int64_t pts;

    /**
     * DTS copied from the AVPacket that triggered returning this frame.
     * 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;

    /**
     * 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;

    /**
     * reordered opaque 64 bits.
     */
    int64_t reordered_opaque;

    /**
     * Sample rate of the audio data.
     */
    int sample_rate;

    /**
     * Channel layout of the audio data.
     */
    uint64_t channel_layout;

    /**
     * AVBuffer references backing the data for this frame. 
	 * If all elements of this array are NULL, 
     * then this frame is not reference counted.
     */
    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;

/**
 * The frame data may be corrupted, e.g. due to decoding errors.
 */
#define AV_FRAME_FLAG_CORRUPT       (1 << 0)
/**
 * A flag to mark the frames which need to be decoded.
 */
#define AV_FRAME_FLAG_DISCARD   (1 << 2)

    /**
     * Frame flags, a combination of @ref lavu_frame_flags
     */
    int flags;

    /**
     * MPEG vs JPEG YUV range.
     * - encoding: Set by user
     * - decoding: Set by libavcodec
     */
    enum AVColorRange color_range;

    enum AVColorPrimaries color_primaries;

    enum AVColorTransferCharacteristic color_trc;

    /**
     * YUV colorspace type.
     * - encoding: Set by user
     * - decoding: Set by libavcodec
     */
    enum AVColorSpace colorspace;

    enum AVChromaLocation chroma_location;

    /**
     * frame timestamp estimated using various heuristics, in stream time base
     * - 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
     * - encoding: unused
     * - decoding: Read by user.
     */
    int64_t pkt_pos;

    /**
     * duration of the corresponding packet, expressed in
     * AVStream->time_base units, 0 if unknown.
     * - encoding: unused
     * - decoding: Read by user.
     */
    int64_t pkt_duration;

    /**
     * metadata.
     * - 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.
     */
    int decode_error_flags;
#define FF_DECODE_ERROR_INVALID_BITSTREAM   1
#define FF_DECODE_ERROR_MISSING_REFERENCE   2
#define FF_DECODE_ERROR_CONCEALMENT_ACTIVE  4
#define FF_DECODE_ERROR_DECODE_SLICES       8

    // number of audio channels, only used for audio.
    int channels;

    // size of the corresponding packet containing the compressed frame.
    int pkt_size;

    /**
     * For hwaccel-format frames, this should be a reference to the
     * AVHWFramesContext describing the frame.
     */
    AVBufferRef *hw_frames_ctx;

    /**
     * AVBufferRef for free use by the API user. FFmpeg will never check the
     * contents of the buffer ref. FFmpeg calls av_buffer_unref() on it when
     * the frame is unreferenced. av_frame_copy_props() calls create a new
     * reference with av_buffer_ref() for the target frame's opaque_ref field.
     */
    AVBufferRef *opaque_ref;

    /**
     * Video frames only. The number of pixels to discard from the the
     * top/bottom/left/right border of the frame to obtain the sub-rectangle of
     * the frame intended for presentation.
     */
    size_t crop_top;
    size_t crop_bottom;
    size_t crop_left;
    size_t crop_right;

    /**
     * AVBufferRef for internal use by a single libav* library.
     * Must not be used to transfer data between libraries.
     */
    AVBufferRef *private_ref;
} AVFrame;

其中，帧类型使用AVPictureType(位于libavutil/avutil.h)表示，枚举定义如下：

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
};

AVFrame的分配与释放也有相应API，具体API以及使用实例如下：

API:
AVFrame *av_frame_alloc(void);
void av_frame_free(AVFrame **frame);

demo:
AVFrame *frame = av_frame_alloc();
av_frame_free(&frame);

标签：AVpacket,audio,int,frame,源码,av,AVFrame,data
来源： https://blog.csdn.net/u011686167/article/details/121551041

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