封装API：avformat_write_header，av_write_trailer，av_interleaved_write

封装API：avformat_write_header，av_write_trailer，av_interleaved_write_frame

avformat_write_header 写头部，

FFmpeg源码分析：写媒体文件头avformat_write_header()_ffmpeg 加入header-CSDN博客

原型

/**
* 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);

函数作用：

* Allocate the stream private data and write the stream header to an output media file.

在复用时，写文件的头部，这个文件指的就是 mp4,等具体文件的头部。

在使用时，AVDictionary 一般用于特殊具体的mp4，MP3等的特殊参数，

而通用的参数一般都在 AVFormatContext 中设置好

参数

AVFormatContext *s, 给那个头部写

AVDictionary **options 其他参数

返回值

negative AVERROR on failure.

成功 AVSTREAM_INIT_IN_WRITE_HEADER (对应0)

或 AVSTREAM_INIT_IN_INIT_OUTPUT （对应1）

av_interleaved_write_frame

原型

/**
* 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);

函数作用

av_interleaved_write_frame是FFmpeg库中的一个函数，用于将一个已编码的媒体数据包（AVPacket）写入到输出媒体文件或流中。
此函数特别关注于维护正确的交错（interleaving）顺序，即确保视频和音频帧按照它们应该播放的顺序被写入，这对于生成可正确播放的多媒体文件至关重要。

参数

AVFormatContext *s, 写入到 AVFormatContext 中

AVPacket *pkt 已编码的媒体数据包（AVPacket）

返回值

* @return 0 on success, a negative AVERROR on error. Libavformat will always
* take care of freeing the packet, even if this function fails.

av_write_trailer 写尾部

原型

/**
* 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);