AVStream是儲存每一個影片/音訊資訊的結構體。
/**
* Stream structure.
* New fields can be added to the end with minor version bumps.
* Removal, reordering and changes to existing fields require a major
* version bump.
* sizeof(AVStream) must not be used outside libav*.
*/
typedef struct AVStream {
int index; /**< stream index in AVFormatContext */
/**
* Format-specific stream ID.
* decoding: set by libavformat
* encoding: set by the user
*/
int id;
AVCodecContext *codec; /**< codec context */
/**
* Real base framerate of the stream.
* This is the lowest framerate with which all timestamps can be
* represented accurately (it is the least common multiple of all
* framerates in the stream). Note, this value is just a guess!
* For example, if the time base is 1/90000 and all frames have either
* approximately 3600 or 1800 timer ticks, then r_frame_rate will be 50/1.
*/
AVRational r_frame_rate;
void *priv_data;
/**
* encoding: pts generation when outputting stream
*/
struct AVFrac pts;
/**
* This is the fundamental unit of time (in seconds) in terms
* of which frame timestamps are represented. For fixed-fps content,
* time base should be 1/framerate and timestamp increments should be 1.
* decoding: set by libavformat
* encoding: set by libavformat in av_write_header
*/
AVRational time_base;
/**
* Decoding: pts of the first frame of the stream in presentation order, in stream time base.
* Only set this if you are absolutely 100% sure that the value you set
* it to really is the pts of the first frame.
* This may be undefined (AV_NOPTS_VALUE).
* @note The ASF header does NOT contain a correct start_time the ASF
* demuxer must NOT set this.
*/
int64_t start_time;
/**
* Decoding: duration of the stream, in stream time base.
* If a source file does not specify a duration, but does specify
* a bitrate, this value will be estimated from bitrate and file size.
*/
int64_t duration;
int64_t nb_frames; ///< number of frames in this stream if known or 0
int disposition; /**< AV_DISPOSITION_* bit field */
enum AVDiscard discard; ///< Selects which packets can be discarded at will and do not need to be demuxed.
/**
* sample aspect ratio (0 if unknown)
* - encoding: Set by user.
* - decoding: Set by libavformat.
*/
AVRational sample_aspect_ratio;
AVDictionary *metadata;
/**
* Average framerate
*/
AVRational avg_frame_rate;
/**
* For streams with AV_DISPOSITION_ATTACHED_PIC disposition, this packet
* will contain the attached picture.
*
* decoding: set by libavformat, must not be modified by the caller.
* encoding: unused
*/
AVPacket attached_pic;
/*****************************************************************
* All fields below this line are not part of the public API. They
* may not be used outside of libavformat and can be changed and
* removed at will.
* New public fields should be added right above.
*****************************************************************
*/
/**
* Stream information used internally by av_find_stream_info()
*/
#define MAX_STD_TIMEBASES (60*12+5)
struct {
int64_t last_dts;
int64_t duration_gcd;
int duration_count;
double duration_error[2][2][MAX_STD_TIMEBASES];
int64_t codec_info_duration;
int nb_decoded_frames;
int found_decoder;
} *info;
int pts_wrap_bits; /**< number of bits in pts (used for wrapping control) */
// Timestamp generation support:
/**
* Timestamp corresponding to the last dts sync point.
*
* Initialized when AVCodecParserContext.dts_sync_point >= 0 and
* a DTS is received from the underlying container. Otherwise set to
* AV_NOPTS_VALUE by default.
*/
int64_t reference_dts;
int64_t first_dts;
int64_t cur_dts;
int64_t last_IP_pts;
int last_IP_duration;
/**
* Number of packets to buffer for codec probing
*/
#define MAX_PROBE_PACKETS 2500
int probe_packets;
/**
* Number of frames that have been demuxed during av_find_stream_info()
*/
int codec_info_nb_frames;
/**
* Stream Identifier
* This is the MPEG-TS stream identifier +1
* 0 means unknown
*/
int stream_identifier;
int64_t interleaver_chunk_size;
int64_t interleaver_chunk_duration;
/* av_read_frame() support */
enum AVStreamParseType need_parsing;
struct AVCodecParserContext *parser;
/**
* last packet in packet_buffer for this stream when muxing.
*/
struct AVPacketList *last_in_packet_buffer;
AVProbeData probe_data;
#define MAX_REORDER_DELAY 16
int64_t pts_buffer[MAX_REORDER_DELAY+1];
AVIndexEntry *index_entries; /**< Only used if the format does not
support seeking natively. */
int nb_index_entries;
unsigned int index_entries_allocated_size;
/**
* flag to indicate that probing is requested
* NOT PART OF PUBLIC API
*/
int request_probe;
} AVStream;
AVStream重要的變數如下所示:
int index:標識該影片/音訊流在AVFormatContext中的索引。
int id:表示流的格式特定ID。在解碼時由libavformat設定,在編碼時由使用者設定
codec (ACCodecContext指標):指向編解碼器上下文的指標。
r_frame_rate(AVRational):流的實際基礎幀率。這是能夠準確表示所有時間戳的最低幀率。
priv_data(void指標):私有資料指標。
pts(AVFrac結構體)：用於輸出流時的PTS生成。
time_base(AVRational):表示時間戳的基本單位(以秒為單位)。解碼時由libavformat設定,在av_write_header中由libavformat設定。
start_time(int64_t):流的第一幀在呈現順序中的PTS(演示時間基準)
duration(int64_t):流的持續時間,以流時間基準表示。
nb_frames(int64_t):如果已知,表示流中的幀數。
disposition(int):AV_DISPOSITION_*位欄位,表示流的性質。
discard(AVDiscard列舉)：選擇可以隨意丟棄的資料包。
sample_aspect_ratio(AVRational):樣本寬高比。
metadata(AVDictionary指標)：後設資料。
avg_frame_rate(AVRational):平均幀率
attached_pic(AVPacket):用於具有AV_DISPOSITION_ATTACHED_PIC性質的流中的附加圖片。
info(內部使用結構體)：內部結構,用於av__find_stream_info()。
pts_wrap_bits(int):PTS位數。
reference_dts,first_dts,cur——dts，last——IP_pts，last_IP_duration(int64_t型別)時間戳生成支援相關。
probe_packets(int):用於編解碼器探測的資料包流量。
codec_info_nb_frames:在av_find_stream_info()期間解混的幀數。
stream_identifier:流識別符號
interleaver_chunk_size,interleaver_chunk_duration:交錯塊大小和持續時間。
need_parsing(AVStreamParseType列舉)：av_read_frame()支援相關。
parser(AVCodecParserContext指標):解析器。
last_in_packet_buffer(AVPacketList指標)：用於複用時流的最後一個包。
probe_data:探測資料。
pts_buffer:PTS緩衝區。
index_entries:僅在格式不支援本地定址時使用。
nb_index_entries:索引條目數。
index_entries_allocated_size(unsigned int):分配給索引條目的記憶體大小。
request_probe(int):指示是否請求探測的標誌。
以上的欄位用於描述音影片流的各種屬性和後設資料,以便在處理和解碼音影片檔案時進行有效的管理和操作。