static int s302m_encode2_frame(AVCodecContext *avctx, AVPacket *avpkt,
                               const AVFrame *frame, int *got_packet_ptr)
{
    S302MEncContext *s = avctx->priv_data;
    const int buf_size = AES3_HEADER_LEN +
                        (frame->nb_samples *
                         avctx->channels *
                        (avctx->bits_per_raw_sample + 4)) / 8;
    int ret, c, channels;
    uint8_t *o;
    PutBitContext pb;

    if ((ret = ff_alloc_packet2(avctx, avpkt, buf_size)) < 0)
        return ret;

    o = avpkt->data;
    init_put_bits(&pb, o, buf_size * 8);
    put_bits(&pb, 16, buf_size - AES3_HEADER_LEN);
    put_bits(&pb, 2, (avctx->channels - 2) >> 1);   // number of channels
    put_bits(&pb, 8, 0);                            // channel ID
    put_bits(&pb, 2, (avctx->bits_per_raw_sample - 16) / 4); // bits per samples (0 = 16bit, 1 = 20bit, 2 = 24bit)
    put_bits(&pb, 4, 0);                            // alignments
    flush_put_bits(&pb);
    o += AES3_HEADER_LEN;

    if (avctx->bits_per_raw_sample == 24) {
        const uint32_t *samples = (uint32_t *)frame->data[0];

        for (c = 0; c < frame->nb_samples; c++) {
            uint8_t vucf = s->framing_index == 0 ? 0x10: 0;

            for (channels = 0; channels < avctx->channels; channels += 2) {
                o[0] = ff_reverse[(samples[0] & 0x0000FF00) >> 8];
                o[1] = ff_reverse[(samples[0] & 0x00FF0000) >> 16];
                o[2] = ff_reverse[(samples[0] & 0xFF000000) >> 24];
                o[3] = ff_reverse[(samples[1] & 0x00000F00) >> 4] | vucf;
                o[4] = ff_reverse[(samples[1] & 0x000FF000) >> 12];
                o[5] = ff_reverse[(samples[1] & 0x0FF00000) >> 20];
                o[6] = ff_reverse[(samples[1] & 0xF0000000) >> 28];
                o += 7;
                samples += 2;
            }

            s->framing_index++;
            if (s->framing_index >= 192)
                s->framing_index = 0;
        }
    } else if (avctx->bits_per_raw_sample == 20) {
        const uint32_t *samples = (uint32_t *)frame->data[0];

        for (c = 0; c < frame->nb_samples; c++) {
            uint8_t vucf = s->framing_index == 0 ? 0x80: 0;

            for (channels = 0; channels < avctx->channels; channels += 2) {
                o[0] = ff_reverse[ (samples[0] & 0x000FF000) >> 12];
                o[1] = ff_reverse[ (samples[0] & 0x0FF00000) >> 20];
                o[2] = ff_reverse[((samples[0] & 0xF0000000) >> 28) | vucf];
                o[3] = ff_reverse[ (samples[1] & 0x000FF000) >> 12];
                o[4] = ff_reverse[ (samples[1] & 0x0FF00000) >> 20];
                o[5] = ff_reverse[ (samples[1] & 0xF0000000) >> 28];
                o += 6;
                samples += 2;
            }

            s->framing_index++;
            if (s->framing_index >= 192)
                s->framing_index = 0;
        }
    } else if (avctx->bits_per_raw_sample == 16) {
        const uint16_t *samples = (uint16_t *)frame->data[0];

        for (c = 0; c < frame->nb_samples; c++) {
            uint8_t vucf = s->framing_index == 0 ? 0x10 : 0;

            for (channels = 0; channels < avctx->channels; channels += 2) {
                o[0] = ff_reverse[ samples[0] & 0xFF];
                o[1] = ff_reverse[(samples[0] & 0xFF00) >>  8];
                o[2] = ff_reverse[(samples[1] & 0x0F)   <<  4] | vucf;
                o[3] = ff_reverse[(samples[1] & 0x0FF0) >>  4];
                o[4] = ff_reverse[(samples[1] & 0xF000) >> 12];
                o += 5;
                samples += 2;

            }

            s->framing_index++;
            if (s->framing_index >= 192)
                s->framing_index = 0;
        }
    }

    *got_packet_ptr = 1;

    return 0;
}