Function av_resample

libavcodec/resample2.c:214–302

}

int av_resample(AVResampleContext *c, short *dst, short *src, int *consumed, int src_size, int dst_size, int update_ctx){
    int dst_index, i;
    int index= c->index;
    int frac= c->frac;
    int dst_incr_frac= c->dst_incr % c->src_incr;
    int dst_incr=      c->dst_incr / c->src_incr;
    int compensation_distance= c->compensation_distance;

  if(compensation_distance == 0 && c->filter_length == 1 && c->phase_shift==0){
        int64_t index2= ((int64_t)index)<<32;
        int64_t incr= (1LL<<32) * c->dst_incr / c->src_incr;
        dst_size= FFMIN(dst_size, (src_size-1-index) * (int64_t)c->src_incr / c->dst_incr);

        for(dst_index=0; dst_index < dst_size; dst_index++){
            dst[dst_index] = src[index2>>32];
            index2 += incr;
        }
        frac += dst_index * dst_incr_frac;
        index += dst_index * dst_incr;
        index += frac / c->src_incr;
        frac %= c->src_incr;
  }else{
    for(dst_index=0; dst_index < dst_size; dst_index++){
        FELEM *filter= c->filter_bank + c->filter_length*(index & c->phase_mask);
        int sample_index= index >> c->phase_shift;
        FELEM2 val=0;

        if(sample_index < 0){
            for(i=0; i<c->filter_length; i++)
                val += src[FFABS(sample_index + i) % src_size] * filter[i];
        }else if(sample_index + c->filter_length > src_size){
            break;
        }else if(c->linear){
            FELEM2 v2=0;
            for(i=0; i<c->filter_length; i++){
                val += src[sample_index + i] * (FELEM2)filter[i];
                v2  += src[sample_index + i] * (FELEM2)filter[i + c->filter_length];
            }
            val+=(v2-val)*(FELEML)frac / c->src_incr;
        }else{
            for(i=0; i<c->filter_length; i++){
                val += src[sample_index + i] * (FELEM2)filter[i];
            }
        }

#ifdef CONFIG_RESAMPLE_AUDIOPHILE_KIDDY_MODE
        dst[dst_index] = av_clip_int16(lrintf(val));
#else
        val = (val + (1<<(FILTER_SHIFT-1)))>>FILTER_SHIFT;
        dst[dst_index] = (unsigned)(val + 32768) > 65535 ? (val>>31) ^ 32767 : val;
#endif

        frac += dst_incr_frac;
        index += dst_incr;
        if(frac >= c->src_incr){
            frac -= c->src_incr;
            index++;
        }