AVPacket:存儲一幀壓縮編碼數據 AVPacket 結構體定義在ffmpeg/libavcodec/packet.h中 /*** 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).** The semantics of data ownership depends on the buf field.* If it is set, the packet data is dynamically allocated and is* valid indefinitely until a call to av_packet_unref() reduces the* reference count to 0.** If the buf field is not set av_packet_ref() would make a copy instead* of increasing the reference count.** The side data is always allocated with av_malloc(), copied by* av_packet_ref() and freed by av_packet_unref().** sizeof(AVPacket) being a part of the public ABI is deprecated. once* av_init_packet() is removed, new packets will only be able to be allocated* with av_packet_alloc(), and new fields may be added to the end of the struct* with a minor bump.** @see av_packet_alloc* @see av_packet_ref* @see av_packet_unref*/ typedef struct AVPacket {/*** A reference to the reference-counted buffer where the packet data is* stored.* May be NULL, then the packet data is not reference-counted.*/AVBufferRef *buf;/*** Presentation timestamp in AVStream->time_base units; the time at which* the decompressed packet will be presented to the user.* Can be AV_NOPTS_VALUE if it is not stored in the file.* pts MUST be larger or equal to dts as presentation cannot happen before* decompression, unless one wants to view hex dumps. Some formats misuse* the terms dts and pts/cts to mean something different. Such timestamps* must be converted to true pts/dts before they are stored in AVPacket.*///顯示時間戳int64_t pts;/*** Decompression timestamp in AVStream->time_base units; the time at which* the packet is decompressed.* Can be AV_NOPTS_VALUE if it is not stored in the file.*///解碼時間戳int64_t dts;//壓縮編碼的數據uint8_t *data;//data的大小int size;//標識該AVPacket所屬的視頻/音頻流int stream_index;/*** A combination of AV_PKT_FLAG values*/int flags;/*** Additional packet data that can be provided by the container.* Packet can contain several types of side information.*/AVPacketSideData *side_data;int side_data_elems;/*** Duration of this packet in AVStream->time_base units, 0 if unknown.* Equals next_pts - this_pts in presentation order.*/int64_t duration;int64_t pos; ///< byte position in stream, -1 if unknown } AVPacket;

跟這個結構體相關的三個函數為：
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AVPacket *av_packet_alloc(void); 創建一個AVPacket并將其字段設置為默認值。使用av_packet_free()釋放內存 int av_packet_ref(AVPacket *dst, const AVPacket *src); 創建一個src->data的新的引用計數。如果src已經設置了引用計數發（src->buffer不為空），則直接將其引用計數+1；如果src沒有設置引用計數（src->buffer為空），則為dst創建一個新的引用計數buf，并復制src->data到buf->buffer中。最后，復制src的其他字段到dst中。 void av_packet_unref(AVPacket *pkt); 將緩存空間的引用計數-1，并將Packet中的其他字段設為初始值。如果引用計數為0，自動的釋放緩存空間。 void av_packet_free(AVPacket **pkt); 釋放數據包，如果數據包是引用計數的，它將首先被取消引用。

參考：FFmpeg: AVPacket

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