FFMpeg copy streams without transcode

Question

I\'m trying to copy all streams from several files into one file without transcoding streams. Something you usually do with ffmpeg utility by ffmpeg -i “f

Answer 1

The reason is because you didn't set the encoder's codec_tag correctly.

You should set the correct codec_tag, or set the codec_tag to 0 and leave the muxer to handle for you.

Following is a sample code how to do.

AVFormatContext *ofmt_ctx; // todo
AVCodec *oc; // todo

AVStream *stream = avformat_new_stream(ofmt_ctx, oc);

if (stream != NULL) {
    // ...
    unsigned int tag = 0;
    // for ffmpeg new api 3.x
    AVCodecParameters *parameters = stream->codecpar;
    if (av_codec_get_tag2(ofmt_ctx->oformat->codec_tag, oc->id, &tag) == 0) {
        av_log(NULL, AV_LOG_ERROR, "could not find codec tag for codec id %d, default to 0.\n", oc->id);
    }
    parameters->codec_tag = tag;
    stream->codec = avcodec_alloc_context3(oc);
    // more setting for stream->codec
    avcodec_parameters_to_context(stream->codec, parameters);

    // for old ffmpeg version
    stream->codec->codec_tag = tag;
    // ...
}