int stereo2mono(unsigned char *buf_stereo, int stereo_size, int bit)
{
    int i = 0;
    int j = 0;
    switch (bit>>3){
    case 1:
        for (; j < stereo_size; j += 2) {
			buf_stereo[i++] = buf_stereo[j];
		}
        break;
    case 2:
        for (; j < stereo_size; j += 4) {
			buf_stereo[i++] = buf_stereo[j];
			buf_stereo[i++] = buf_stereo[j+1];
		}
        break;
    case 3:
        for (; j < stereo_size; j += 6) {
			buf_stereo[i++] = buf_stereo[j];
			buf_stereo[i++] = buf_stereo[j+1];
			buf_stereo[i++] = buf_stereo[j+2];
		}
        break;
    case 4:
        for (; j < stereo_size; j += 8) {
			buf_stereo[i++] = buf_stereo[j];
			buf_stereo[i++] = buf_stereo[j+1];
			buf_stereo[i++] = buf_stereo[j+2];
			buf_stereo[i++] = buf_stereo[j+3];
	    }
        break;
    default:
            printf("stereo2mono(): Unsupport bits-per-sample: %i\n", bit);
            return 0;
    }
    
    return stereo_size >> 1;
}

unsigned char *mono2stereo(unsigned char *buf_mono, int mono_size, int bit, int *stereo_size)
{
    int i, j;
    unsigned char *pszBufStereo = NULL;
    *stereo_size = mono_size * 2;
    pszBufStereo = ortp_malloc(*stereo_size);
    if (pszBufStereo == NULL)
    {
        printf("mono2stereo(): Allocate stereo buffer error, size %d\n", *stereo_size);
        return NULL;
    }
    
    i = 0;
    j = 0;
    switch (bit>>3)
    {
        case 1:
            for (; mono_size > 0; mono_size--)
            {
                pszBufStereo[i++] = buf_mono[j];
                pszBufStereo[i++] = buf_mono[j];
                j++;
            }
            break;
            
        case 2:
            for (; mono_size > 0; mono_size -= 2)
            {
                pszBufStereo[i++] = buf_mono[j];
                pszBufStereo[i++] = buf_mono[j+1];
                pszBufStereo[i++] = buf_mono[j];
                pszBufStereo[i++] = buf_mono[j+1];
                j += 2;
            }
            break;
            
        case 3:
            for (; mono_size > 0; mono_size -= 3)
            {
                pszBufStereo[i++] = buf_mono[j];
                pszBufStereo[i++] = buf_mono[j+1];
                pszBufStereo[i++] = buf_mono[j+2];
                pszBufStereo[i++] = buf_mono[j];
                pszBufStereo[i++] = buf_mono[j+1];
                pszBufStereo[i++] = buf_mono[j+2];
                j += 3;
            }
            break;
            
        case 4:
            for (; mono_size > 0; mono_size -= 4)
            {
                pszBufStereo[i++] = buf_mono[j];
                pszBufStereo[i++] = buf_mono[j+1];
                pszBufStereo[i++] = buf_mono[j+2];
                pszBufStereo[i++] = buf_mono[j+3];
                pszBufStereo[i++] = buf_mono[j];
                pszBufStereo[i++] = buf_mono[j+1];
                pszBufStereo[i++] = buf_mono[j+2];
                pszBufStereo[i++] = buf_mono[j+3];
                j += 4;
            }
            break;
            
        default:
            printf("mono2stereo(): Unsupport bits-per-sample: %i\n", bit);
            ortp_free(pszBufStereo);
            return NULL;
    }
    
    return pszBufStereo;
}