ffmpeg-AVStream解析

AVStream是存储在每个视频/音频流信息的结构体

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typedef struct AVStream {
int index; /**AVFormatContext流索引 */

int id;
#if FF_API_LAVF_AVCTX
/**
* @deprecated use the codecpar struct instead
*/
attribute_deprecated
AVCodecContext *codec;
#endif
void *priv_data;

/**
* 时基。通过该值可以把PTS,DTS转化为真正的时间。FFMPEG其他结构体中也有这个字段
* PTS*time_base=真正的时间
*/
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.
*
* Encoding: May be set by the caller before avformat_write_header() to
* provide a hint to the muxer about the estimated duration.
*/
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.

/**
* 采样率(如果未知,该值为0)
*/
AVRational sample_aspect_ratio;

AVDictionary *metadata;

/**
* Average framerate
*
* - demuxing: May be set by libavformat when creating the stream or in
* avformat_find_stream_info().
* - muxing: May be set by the caller before avformat_write_header().
*/
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;

/**
* An array of side data that applies to the whole stream (i.e. the
* container does not allow it to change between packets).
*
* There may be no overlap between the side data in this array and side data
* in the packets. I.e. a given side data is either exported by the muxer
* (demuxing) / set by the caller (muxing) in this array, then it never
* appears in the packets, or the side data is exported / sent through
* the packets (always in the first packet where the value becomes known or
* changes), then it does not appear in this array.
*
* - demuxing: Set by libavformat when the stream is created.
* - muxing: May be set by the caller before avformat_write_header().
*
* Freed by libavformat in avformat_free_context().
*
* @see av_format_inject_global_side_data()
*/
AVPacketSideData *side_data;
/**
* The number of elements in the AVStream.side_data array.
*/
int nb_side_data;

/**
* Flags for the user to detect events happening on the stream. Flags must
* be cleared by the user once the event has been handled.
* A combination of AVSTREAM_EVENT_FLAG_*.
*/
int event_flags;
#define AVSTREAM_EVENT_FLAG_METADATA_UPDATED 0x0001 ///< The call resulted in updated metadata.

/**
* 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;

#if FF_API_LAVF_FFSERVER
/**
* String containing pairs of key and values describing recommended encoder configuration.
* Pairs are separated by ','.
* Keys are separated from values by '='.
*
* @deprecated unused
*/
attribute_deprecated
char *recommended_encoder_configuration;
#endif

/**
* Codec parameters associated with this stream. Allocated and freed by
* libavformat in avformat_new_stream() and avformat_free_context()
* respectively.
*
* - demuxing: filled by libavformat on stream creation or in
* avformat_find_stream_info()
* - muxing: filled by the caller before avformat_write_header()
*/
AVCodecParameters *codecpar;

/*****************************************************************
* 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.
* Internal note: be aware that physically removing these fields
* will break ABI. Replace removed fields with dummy fields, and
* add new fields to AVStreamInternal.
*****************************************************************
*/

#define MAX_STD_TIMEBASES (30*12+30+3+6)
/**
* Stream information used internally by avformat_find_stream_info()
*/
struct {
int64_t last_dts;
int64_t duration_gcd;
int duration_count;
int64_t rfps_duration_sum;
double (*duration_error)[2][MAX_STD_TIMEBASES];
int64_t codec_info_duration;
int64_t codec_info_duration_fields;
int frame_delay_evidence;

/**
* 0 -> decoder has not been searched for yet.
* >0 -> decoder found
* <0 -> decoder with codec_id == -found_decoder has not been found
*/
int found_decoder;

int64_t last_duration;

/**
* Those are used for average framerate estimation.
*/
int64_t fps_first_dts;
int fps_first_dts_idx;
int64_t fps_last_dts;
int fps_last_dts_idx;

} *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 first_dts;
int64_t cur_dts;
int64_t last_IP_pts;
int last_IP_duration;

/**
* Number of packets to buffer for codec probing
*/
int probe_packets;

/**
* Number of frames that have been demuxed during avformat_find_stream_info()
*/
int codec_info_nb_frames;

/* 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;

/**
* Stream Identifier
* This is the MPEG-TS stream identifier +1
* 0 means unknown
*/
int stream_identifier;

/**
* Details of the MPEG-TS program which created this stream.
*/
int program_num;
int pmt_version;
int pmt_stream_idx;

int64_t interleaver_chunk_size;
int64_t interleaver_chunk_duration;

/**
* stream probing state
* -1 -> probing finished
* 0 -> no probing requested
* rest -> perform probing with request_probe being the minimum score to accept.
* NOT PART OF PUBLIC API
*/
int request_probe;
/**
* Indicates that everything up to the next keyframe
* should be discarded.
*/
int skip_to_keyframe;

/**
* Number of samples to skip at the start of the frame decoded from the next packet.
*/
int skip_samples;

/**
* If not 0, the number of samples that should be skipped from the start of
* the stream (the samples are removed from packets with pts==0, which also
* assumes negative timestamps do not happen).
* Intended for use with formats such as mp3 with ad-hoc gapless audio
* support.
*/
int64_t start_skip_samples;

/**
* If not 0, the first audio sample that should be discarded from the stream.
* This is broken by design (needs global sample count), but can't be
* avoided for broken by design formats such as mp3 with ad-hoc gapless
* audio support.
*/
int64_t first_discard_sample;

/**
* The sample after last sample that is intended to be discarded after
* first_discard_sample. Works on frame boundaries only. Used to prevent
* early EOF if the gapless info is broken (considered concatenated mp3s).
*/
int64_t last_discard_sample;

/**
* Number of internally decoded frames, used internally in libavformat, do not access
* its lifetime differs from info which is why it is not in that structure.
*/
int nb_decoded_frames;

/**
* Timestamp offset added to timestamps before muxing
* NOT PART OF PUBLIC API
*/
int64_t mux_ts_offset;

/**
* Internal data to check for wrapping of the time stamp
*/
int64_t pts_wrap_reference;

/**
* Options for behavior, when a wrap is detected.
*
* Defined by AV_PTS_WRAP_ values.
*
* If correction is enabled, there are two possibilities:
* If the first time stamp is near the wrap point, the wrap offset
* will be subtracted, which will create negative time stamps.
* Otherwise the offset will be added.
*/
int pts_wrap_behavior;

/**
* Internal data to prevent doing update_initial_durations() twice
*/
int update_initial_durations_done;

/**
* Internal data to generate dts from pts
*/
int64_t pts_reorder_error[MAX_REORDER_DELAY+1];
uint8_t pts_reorder_error_count[MAX_REORDER_DELAY+1];

/**
* Internal data to analyze DTS and detect faulty mpeg streams
*/
int64_t last_dts_for_order_check;
uint8_t dts_ordered;
uint8_t dts_misordered;

/**
* Internal data to inject global side data
*/
int inject_global_side_data;

/**
* display aspect ratio (0 if unknown)
* - encoding: unused
* - decoding: Set by libavformat to calculate sample_aspect_ratio internally
*/
AVRational display_aspect_ratio;

/**
* An opaque field for libavformat internal usage.
* Must not be accessed in any way by callers.
*/
AVStreamInternal *internal;
} AVStream;