int rtjpeg_decode_frame_yuv420(RTJpegContext *c, AVFrame *f,

                               const uint8_t *buf, int buf_size) {

    GetBitContext gb;

    int w = c->w / 16, h = c->h / 16;

    int x, y;

    uint8_t *y1 = f->data[0], *y2 = f->data[0] + 8 * f->linesize[0];

    uint8_t *u = f->data[1], *v = f->data[2];

    init_get_bits(&gb, buf, buf_size * 8);

    for (y = 0; y < h; y++) {

        for (x = 0; x < w; x++) {

            DCTELEM *block = c->block;

            if (get_block(&gb, block, c->scan, c->lquant) > 0)

                c->dsp->idct_put(y1, f->linesize[0], block);

            y1 += 8;

            if (get_block(&gb, block, c->scan, c->lquant) > 0)

                c->dsp->idct_put(y1, f->linesize[0], block);

            y1 += 8;

            if (get_block(&gb, block, c->scan, c->lquant) > 0)

                c->dsp->idct_put(y2, f->linesize[0], block);

            y2 += 8;

            if (get_block(&gb, block, c->scan, c->lquant) > 0)

                c->dsp->idct_put(y2, f->linesize[0], block);

            y2 += 8;

            if (get_block(&gb, block, c->scan, c->cquant) > 0)

                c->dsp->idct_put(u, f->linesize[1], block);

            u += 8;

            if (get_block(&gb, block, c->scan, c->cquant) > 0)

                c->dsp->idct_put(v, f->linesize[2], block);

            v += 8;

        }

        y1 += 2 * 8 * (f->linesize[0] - w);

        y2 += 2 * 8 * (f->linesize[0] - w);

        u += 8 * (f->linesize[1] - w);

        v += 8 * (f->linesize[2] - w);

    }

    return get_bits_count(&gb) / 8;

}
