Muxing AVPackets into mp4 file

Question

I am developing a tool which receives a h.264 live stream from the network (the sender is a hardware encoder), buffers the last x-minutes and creates a video file of the last x-

Answer 1

This might not be the case, but avformat_write_header function should be used for writing header instead of function pointer in AVOutputFormat.write_header

Answer 2

This is a general scheme shows how to mux video file from an existing packets

AVOutputFormat * outFmt = av_guess_format("mp4", NULL, NULL);
AVFormatContext *outFmtCtx = NULL;
avformat_alloc_output_context2(&outFmtCtx, outFmt, NULL, NULL);
AVStream * outStrm = av_new_stream(outFmtCtx, 0);

AVCodec * codec = NULL;
avcodec_get_context_defaults3(outStrm->codec, codec);
outStrm->codec->coder_type = AVMEDIA_TYPE_VIDEO;

///....
/// set some required value, such as
/// outStrm->codec->flags
/// outStrm->codec->sample_aspect_ratio
/// outStrm->disposition
/// outStrm->codec->codec_tag
/// outStrm->codec->bits_per_raw_sample
/// outStrm->codec->chroma_sample_location
/// outStrm->codec->codec_id
/// outStrm->codec->codec_tag
/// outStrm->codec->time_base
/// outStrm->codec->extradata 
/// outStrm->codec->extradata_size
/// outStrm->codec->pix_fmt
/// outStrm->codec->width
/// outStrm->codec->height
/// outStrm->codec->sample_aspect_ratio
/// see ffmpeg.c for details  

avio_open(&outFmtCtx->pb, outputFileName, AVIO_FLAG_WRITE);

avformat_write_header(outFmtCtx, NULL);

for (...)
{
av_write_frame(outFmtCtx, &pkt);
}

av_write_trailer(outFmtCtx);
avio_close(outFmtCtx->pb);
avformat_free_context(outFmtCtx);

For troubleshooting, it is useful to set detailed logging: av_log_set_level(AV_LOG_DEBUG);