开发笔记:FFmpeg结构体学习：AVStream分析

/**
* 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; /***/
/**
* Format-specific stream ID.
* decoding: set by libavformat
* encoding: set by the user
*/
int id;
AVCodecContext *codec; /***/
/**
* 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; ///
int disposition; /***/

enum AVDiscard discard; ///
/**
* 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; /***/

// 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; /** 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;