avformat_write_header is not working properly in ffmepg - c

Question

I was working on mp4 file creation project using FFMPEG, i tried to convert the stream information of video packet based on FFMPEG muxing,remuxing code, but header get damaged after convert into so file is corrupted.
/* this code used to set the stream information */
AVFormatContext *input_context,*output_context;
AVDictionary *opt;
AVStream *out_stream;
AVCodecContext *newcontext = NULL;
out_stream= avformat_new_stream(output_context,NULL);
newcontext = avcodec_alloc_context3(codec);
newcontext->codec_id=Output_fmt->video_codec;
newcontext->bit_rate =in_stream->codec->bit_rate;
newcontext->width = in_stream->codec->width;
newcontext->height = in_stream->codec->height;
newcontext->timecode_frame_start = in_stream->codec->timecode_frame_start;
newcontext->gop_size = in_stream->codec->gop_size;
newcontext->profile = in_stream->codec->profile;
newcontext->level = in_stream->codec->level;
newcontext->pix_fmt = PIX_FMT_YUV420P;
newcontext->frame_size = in_stream->codec->frame_size;
newcontext->sample_fmt = in_stream->codec->sample_fmt;
newcontext->sample_rate = in_stream->codec->sample_rate;
time_base = (double)in_stream->time_base.num / (double)in_stream->time_base.den;
duration = (double)in_stream->duration * time_base * 1000.0;
if (!out_stream) {
fprintf(stderr, "Failed allocating output stream\n");
ret = AVERROR_UNKNOWN;
return;
}
ret = avcodec_copy_context(out_stream->codec,newcontext);
if (ret < 0) {
fprintf(stderr, "Failed to copy context from input to output stream codec context\n");
goto end;
}
out_stream->codec->codec_tag = 0;
if (output_context->oformat->flags & AVFMT_GLOBALHEADER)
out_stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
Changed the Header Information using:
/* this code used to set the metadata */
av_dict_set(&opt, "major_brand", "mp42", 0);
av_dict_set(&opt, "minor_version","512" , 0);
av_dict_set(&opt, "compatible_brands","isomiso2avc1mp41",0);
av_dict_set(&opt, "comment","Hash=855738390",0);
output_context->metadata = opt;
ret = avformat_write_header(output_context,NULL);
after create the mp4 file check file using ffmpeg in terminal. getting Error like this:
/this error message/
[mpeg4 # 0x7ff2b9811c00] header damaged Last message repeated 39
times [mov,mp4,m4a,3gp,3g2,mj2 # 0x7ff2ba800000] decoding for stream 0
failed [mov,mp4,m4a,3gp,3g2,mj2 # 0x7ff2ba800000] Could not find codec
parameters for stream 0 (Video: mpeg4 (mp4v / 0x7634706D), none, 376
kb/s): unspecified size Consider increasing the value for the
'analyzeduration' and 'probesize' options.

Answer 1

Easiest thing is to just download a freeware hex editor (for your specific O.S). Next is use desktop (commandline) version of FFmpeg (download a static build)
Use the commandline FFmpeg to convert Source to MP4 (ie: as mp4_ffmpeg.mp4)
Use your code to convert Source to MP4 (ie: as mp4_code.mp4)
Open both mp4_ffmpeg.mp4 & mp4_code.mp4 and compare bytes. The working one should be mp4_ffmpeg.mp4 so what's different from bytes produced with your code?
Things to look for :
All begin with ftyp?
moov is header and should be at start (sometimes at back after mdat which holds all a/v data in one chunk. To move the header of any mp4 to front or beginning bytes then use -movflags +faststart for example in commandline use : ffmpeg -i myfile.avi -movflags +faststart newfile.mp4)
Before each of the words moov or mdat, the previous 4 bytes are the size (in bytes) after you skip the 4 letters of word... are these sizes correct?
Do you have all the MP4 atoms (metadata sections) defined? They match what FFmpeg produced for its version of the MP4 converting?