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

[Carl Eugen Hoyos]

Am Di., 17. März 2020 um 23:16 Uhr schrieb Anton Shekhovtsov
<shekh.anton at gmail.com>:
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>
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> 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?
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> 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;

As explained, this will not fail for some invalid combinations.

Carl Eugen