static av_cold int validate_options(AVCodecContext *avctx, AC3EncodeContext *s)
{
    int freq = avctx->sample_rate;
    int bitrate = avctx->bit_rate;
    int i, j;

    if (!avctx->channel_layout) {
        av_log(avctx, AV_LOG_WARNING, "No channel layout specified. The "
                                      "encoder will guess the layout, but it "
                                      "might be incorrect.\n");
    }
    if (set_channel_info(s, avctx->channels, &avctx->channel_layout)) {
        av_log(avctx, AV_LOG_ERROR, "invalid channel layout\n");
        return -1;
    }

    /* frequency */
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++)
            if ((ff_ac3_sample_rate_tab[j] >> i) == freq)
                goto found;
    }
    return -1;
 found:
    s->sample_rate        = freq;
    s->bit_alloc.sr_shift = i;
    s->bit_alloc.sr_code  = j;
    s->bitstream_id       = 8 + s->bit_alloc.sr_shift;
    s->bitstream_mode     = 0; /* complete main audio service */

    /* bitrate & frame size */
    for (i = 0; i < 19; i++) {
        if ((ff_ac3_bitrate_tab[i] >> s->bit_alloc.sr_shift)*1000 == bitrate)
            break;
    }
    if (i == 19)
        return -1;
    s->bit_rate        = bitrate;
    s->frame_size_code = i << 1;

    return 0;
}