AVPacket
AVPacket是儲存壓縮編碼資料相關資訊的結構體。
typedef struct AVPacket {
/**
* 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.
*/
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.
*/
int64_t dts;
uint8_t *data;
int size;
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.
*/
struct {
uint8_t *data;
int size;
enum AVPacketSideDataType type;
} *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.
*/
int duration;
void (*destruct)(struct AVPacket *);
void *priv;
int64_t pos; ///< byte position in stream, -1 if unknown
/**
* Time difference in AVStream->time_base units from the pts of this
* packet to the point at which the output from the decoder has converged
* independent from the availability of previous frames. That is, the
* frames are virtually identical no matter if decoding started from
* the very first frame or from this keyframe.
* Is AV_NOPTS_VALUE if unknown.
* This field is not the display duration of the current packet.
* This field has no meaning if the packet does not have AV_PKT_FLAG_KEY
* set.
*
* The purpose of this field is to allow seeking in streams that have no
* keyframes in the conventional sense. It corresponds to the
* recovery point SEI in H.264 and match_time_delta in NUT. It is also
* essential for some types of subtitle streams to ensure that all
* subtitles are correctly displayed after seeking.
*/
int64_t convergence_duration;
} AVPacket;
pts 表示該幀的呈現時間戳(Presentation Timestamp),以AVStream->time_base為單位。即解壓後的幀將呈現給使用者的時間。如果不在檔案中儲存,則可以是AV_NOPTS_VALUE。
dts:表示該幀的解壓時間戳(Decompression Timestamp),以AVStream->time_base為單位。即該幀解壓的時間。如果不在檔案中儲存,則可以是AV_NOPTS_VALUE。
data:指向資料緩衝區的指標。
size:資料緩衝區的大小。
stream_index:表示該幀所屬的流在AVFormatContext中的索引。
flags：標誌位的組合,表示AV_pKT_FLAG的值。
side_data:(AVPacketSideData結構體指標陣列)：指向可以由容器提供的附加包資料的指標陣列。
duration:以AVStream->time_base為單位的該幀的持續時間。如果未知,則為0。
destruct:指向一個函式的指標,用於銷燬AVPacket。
priv:私有資料指標。
pos：該幀在流中的位元組位置,如果未知則為-1.
convergence_duration:表示從該幀的pts到解碼器輸出收斂的時間差。用AVStream->time_base單位表示。如果未知,則為AV_NOPTS_VALUE。這個欄位在沒有傳統關鍵幀的流中進行定位非常重要。