c - Forcing global headers in LibAV -

i'm trying write c program using libav takes input video webcam , saves h264 mp4 file. i'm modifying working program saves .ppm frames webcam. i'm unable convert avpackets may written, though--specifically, avformat_write_header() failing, messages

[mp4 @ 0050c000] codec stream 0 not use global headers container format requires global headers [mp4 @ 0050c000] not find tag codec none in stream #0, codec not supported in container 

the call apparently returning error -22, can find no place error code explained. how can force avformat_write_header() add in global headers when it's trying write mp4? code below; of adapted this question, i'm trying adapt input video file webcam.

int _tmain(int argc, _tchar* argv[]) {     avinputformat *inputformat = null;     avdictionary *inputdictionary= null;     avformatcontext *inputformatctx = null;     avformatcontext *outputformatctx = null;     avcodeccontext *inputcodecctxorig = null;     avcodeccontext *inputcodecctx = null;     avcodeccontext *outputcodecctx;     avcodec *inputcodec = null;     avcodec *outputcodec = null;     avstream *stream = null;     aviocontext *aviocontext = null;     avcodec_register_all();     av_register_all();     avdevice_register_all();     av_dict_set(&inputdictionary, "logitech hd pro webcam c920", "video", 0);     avformat_alloc_output_context2(&outputformatctx, null, null, "output.mp4");     avio_open(&aviocontext, "output.mp4", avio_flag_write);     outputformatctx->pb = aviocontext;     stream = avformat_new_stream(outputformatctx, outputcodec);     inputformat = av_find_input_format("dshow");     int r = avformat_open_input(&inputformatctx, "video=logitech hd pro webcam c920", inputformat, &inputdictionary);     if (r != 0) {         fprintf(stderr, "avformat_open_input() failed error %d!\n", r);         return -1; }     r = avformat_find_stream_info(inputformatctx, null);     if (r != 0) {         fprintf(stderr, "avformat_find_stream_info() failed!\n");         return -1; }     av_dump_format(inputformatctx, 0, "video=logitech hd pro webcam c920", 0);     unsigned int i;     int videostream;     videostream = -1;     (i = 0; < inputformatctx->nb_streams; i++) {         if (inputformatctx->streams[i]->codec->codec_type == avmedia_type_video {             videostream = i;             break; }     }     if (videostream == -1)         { return -1; }     inputcodecctxorig = inputformatctx->streams[videostream]->codec;     inputcodec = avcodec_find_decoder(inputcodecctxorig->codec_id);     if (inputcodec == null) {         fprintf(stderr, "avcodec_find_decoder() failed!\n");         return -1; }     else { printf("supported codec!\n"); }     inputcodecctx = avcodec_alloc_context3(inputcodec);     if (inputcodecctx == null) {         fprintf(stderr, "avcodec_alloc_context3() failed!\n");         return -1; }     if (avcodec_copy_context(inputcodecctx, inputcodecctxorig) != 0) {         fprintf(stderr, "avcodec_copy_context() failed!\n");         return -1; }     if (avcodec_open2(inputcodecctx,inputcodec,&inputdictionary) < 0) {         fprintf(stderr, "avcodec_open2() failed!\n");         return -1; }     outputformatctx->oformat = av_guess_format(null, "output.mp4", null);     outputformatctx->oformat->flags |= avfmt_globalheader;     outputcodecctx = avcodec_alloc_context3(outputcodec);     avcodec_copy_context(outputcodecctx, inputcodecctx);     outputcodec = inputcodec;     avcodec_open2(outputcodecctx, outputcodec, null);     avpacket packet;     printf("foo\n");     int errnum = avformat_write_header(outputformatctx, &inputdictionary);     printf("bar %d\n", errnum);     while(av_read_frame(inputformatctx, &packet)>=0) {         av_interleaved_write_frame(outputformatctx, &packet);         av_free_packet(&packet);     }     avcodec_close(inputcodecctx);     avcodec_close(inputcodecctxorig);     avformat_close_input(&inputformatctx);     return 0; } 

how can force avformat_write_header() add in global headers

global headers written encoder, later muxer reads them codec's extra_data field. should set flag in codec's context, before call avcodec_open2().

outputcodecctx->flags |= av_codec_flag_global_header; 

[mp4 @ 0050c000] not find tag codec none in stream #0, codec not supported in container

you can try setup encoder explicitly (i.e. manually), or copy codeccontext original input codeccontext.

outputcodec = av_codec_find_encoder(av_codec_id_h264); if(!outputcodec) return -1; //no encoder found  outputcodecctx = avcodec_alloc_context3(outputcodec); avcodec_copy_context(outputcodecctx, inputcodecctxorig); //copy orig  //you have make sure each field populated correctly //with debugger or assertations assert(outputcodecctx->codec_id == av_codec_id_h264); //etc  outputcodecctx->flags |= av_codec_flag_global_header; if(avcodec_open2(outputcodecctx, outputcodec, null) <0) return -1;