[Libav-user] How to access the struct AVCodecTag?

[Anton Shekhovtsov]

вт, 17 мар. 2020 г. в 23:51, Giuseppe Torelli <giutorcom at gmail.com>:

>
>> I'm not sure if this is completely sane but I'm using this method for
>> testing how FFMpeg can mix codec and container: create memory writing
>> context, prepare writing of container, add single stream with the specific
>> encoding format, try to finish.
>> If there is any error assume the format is not supported in the container.
>>
>
> Would you please share some code?
>

https://sourceforge.net/p/vdfiltermod/cch_input/ci/master/tree/export.cpp#l884

This is part of VirtualDub2

    IOWBuffer io;
    int buf_size = 4096;
    void* buf = av_malloc(buf_size);
    AVIOContext* avio_ctx = avio_alloc_context((unsigned
char*)buf,buf_size,1,&io,0,&IOWBuffer::Write,&IOWBuffer::Seek);
    AVFormatContext* ofmt = avformat_alloc_context();
    ofmt->pb = avio_ctx;
    ofmt->oformat = this->ofmt->oformat;
    AVStream* st = avformat_new_stream(ofmt, 0);
    avcodec_parameters_copy(st->codecpar, si.st->codecpar);
    st->sample_aspect_ratio = si.st->sample_aspect_ratio;
    st->avg_frame_rate = si.st->avg_frame_rate;
    av_stream_set_r_frame_rate(st,st->avg_frame_rate);
    st->time_base = si.st->time_base;

    if(st->codecpar->codec_type==AVMEDIA_TYPE_AUDIO){
      if(ofmt->oformat==av_guess_format("mp4", 0, 0)){
        st->codecpar->codec_tag = 0;
      }
    }

    bool failed = true;
    if(avformat_write_header(ofmt, 0)<0) goto cleanup;
    if(av_write_trailer(ofmt)<0) goto cleanup;
    failed = false;

  cleanup:
    av_free(avio_ctx->buffer);
    av_free(avio_ctx);
    avformat_free_context(ofmt);
    if(failed){
      std::string msg;
      msg += avcodec_get_name(codec_id);
      msg += ": codec not currently supported in container ";
      msg += format_name;
      mContext.mpCallbacks->SetError(msg.c_str());
      return false;
    }
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