跟写视频文件相关的三个配套接口是

avformat_write_header()用于写视频文件头

av_write_frame()用于写视频数据

av_interleaved_write_frame() 用于交错写视频数据

av_write_trailer()用于写视频文件尾

avformat_write_header

接口声明位于ffmpeg/libavformat/avformat.h中

/*** Allocate the stream private data and write the stream header to* an output media file.** @param s Media file handle, must be allocated with avformat_alloc_context().*          Its oformat field must be set to the desired output format;*          Its pb field must be set to an already opened AVIOContext.* @param options  An AVDictionary filled with AVFormatContext and muxer-private options.*                 On return this parameter will be destroyed and replaced with a dict containing*                 options that were not found. May be NULL.** @return AVSTREAM_INIT_IN_WRITE_HEADER on success if the codec had not already been fully initialized in avformat_init,*         AVSTREAM_INIT_IN_INIT_OUTPUT  on success if the codec had already been fully initialized in avformat_init,*         negative AVERROR on failure.** @see av_opt_find, av_dict_set, avio_open, av_oformat_next, avformat_init_output.*/
av_warn_unused_result
int avformat_write_header(AVFormatContext *s, AVDictionary **options);

参数含义：

s：用于输出的AVFormatContext。
options：额外的选项，目前没有深入研究过，一般为NULL。

avformat_write_header()的调用关系如下图所示。

avformat_write_header()完成了以下工作：

（1）调用init_muxer()初始化复用器
（2）调用AVOutputFormat的write_header()

具体可以参见：
FFmpeg源代码简单分析：avformat_write_header()

av_write_frame

av_write_frame()用于输出一帧视音频数据，它的声明位于libavformat\avformat.h


/*** Write a packet to an output media file.** This function passes the packet directly to the muxer, without any buffering* or reordering. The caller is responsible for correctly interleaving the* packets if the format requires it. Callers that want libavformat to handle* the interleaving should call av_interleaved_write_frame() instead of this* function.** @param s media file handle* @param pkt The packet containing the data to be written. Note that unlike*            av_interleaved_write_frame(), this function does not take*            ownership of the packet passed to it (though some muxers may make*            an internal reference to the input packet).*            <br>*            This parameter can be NULL (at any time, not just at the end), in*            order to immediately flush data buffered within the muxer, for*            muxers that buffer up data internally before writing it to the*            output.*            <br>*            Packet's @ref AVPacket.stream_index "stream_index" field must be*            set to the index of the corresponding stream in @ref*            AVFormatContext.streams "s->streams".*            <br>*            The timestamps (@ref AVPacket.pts "pts", @ref AVPacket.dts "dts")*            must be set to correct values in the stream's timebase (unless the*            output format is flagged with the AVFMT_NOTIMESTAMPS flag, then*            they can be set to AV_NOPTS_VALUE).*            The dts for subsequent packets passed to this function must be strictly*            increasing when compared in their respective timebases (unless the*            output format is flagged with the AVFMT_TS_NONSTRICT, then they*            merely have to be nondecreasing).  @ref AVPacket.duration*            "duration") should also be set if known.* @return < 0 on error, = 0 if OK, 1 if flushed and there is no more data to flush** @see av_interleaved_write_frame()*/
int av_write_frame(AVFormatContext *s, AVPacket *pkt);

参数含义：

s：用于输出的AVFormatContext。
pkt：等待输出的AVPacket。

具体实现参见：FFmpeg源代码简单分析：av_write_frame()

av_interleaved_write_frame

av_interleaved_write_frame 用于将数据包写入输出媒体文件，确保交错正确。确保包按照dts递增的顺序正确交错

该函数无论成功还是失败，其内部都会调用av_packet_unref解引用

它的声明位于libavformat\avformat.h


/*** Write a packet to an output media file ensuring correct interleaving.** This function will buffer the packets internally as needed to make sure the* packets in the output file are properly interleaved in the order of* increasing dts. Callers doing their own interleaving should call* av_write_frame() instead of this function.** Using this function instead of av_write_frame() can give muxers advance* knowledge of future packets, improving e.g. the behaviour of the mp4* muxer for VFR content in fragmenting mode.** @param s media file handle* @param pkt The packet containing the data to be written.*            <br>*            If the packet is reference-counted, this function will take*            ownership of this reference and unreference it later when it sees*            fit.*            The caller must not access the data through this reference after*            this function returns. If the packet is not reference-counted,*            libavformat will make a copy.*            <br>*            This parameter can be NULL (at any time, not just at the end), to*            flush the interleaving queues.*            <br>*            Packet's @ref AVPacket.stream_index "stream_index" field must be*            set to the index of the corresponding stream in @ref*            AVFormatContext.streams "s->streams".*            <br>*            The timestamps (@ref AVPacket.pts "pts", @ref AVPacket.dts "dts")*            must be set to correct values in the stream's timebase (unless the*            output format is flagged with the AVFMT_NOTIMESTAMPS flag, then*            they can be set to AV_NOPTS_VALUE).*            The dts for subsequent packets in one stream must be strictly*            increasing (unless the output format is flagged with the*            AVFMT_TS_NONSTRICT, then they merely have to be nondecreasing).*            @ref AVPacket.duration "duration") should also be set if known.** @return 0 on success, a negative AVERROR on error. Libavformat will always*         take care of freeing the packet, even if this function fails.** @see av_write_frame(), AVFormatContext.max_interleave_delta*/
int av_interleaved_write_frame(AVFormatContext *s, AVPacket *pkt);

参数含义：

AVFormatContext *s：媒体文件对应的结构上下文

AVPacket *pkt：包含要写入数据的数据包

av_write_trailer

av_write_trailer函数写入文件结束符，并关闭文件，声明位于libavformat\avformat.h


/*** Write the stream trailer to an output media file and free the* file private data.** May only be called after a successful call to avformat_write_header.** @param s media file handle* @return 0 if OK, AVERROR_xxx on error*/
int av_write_trailer(AVFormatContext *s);

FFmpeg源代码：avformat_write_header/av_write_frame/av_interleaved_write_frame/av_write_trailer相关推荐

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FFmpeg源代码：avformat_write_header/av_write_frame/av_interleaved_write_frame/av_write_trailer

avformat_write_header

av_write_frame

av_interleaved_write_frame

av_write_trailer

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