static void choose_sample_rate(AVStream *st, AVCodec *codec)
{
    if(codec && codec->supported_samplerates){
        const int *p= codec->supported_samplerates;
        int best=0;
        int best_dist=INT_MAX;
        for(; *p; p++){
            int dist= abs(st->codec->sample_rate - *p);
            if(dist < best_dist){
                best_dist= dist;
                best= *p;
            }
        }
        if(best_dist){
            av_log(st->codec, AV_LOG_WARNING, "Requested sampling rate unsupported using closest supported (%d)\n", best);
        }
        st->codec->sample_rate= best;
    }
}