static int encode_frame(AVCodecContext *avctx, unsigned char *buf,
                        int buf_size, void *data)
{
    const AVFrame *pic = data;
    int aligned_width = ((avctx->width + 47) / 48) * 48;
    int stride = aligned_width * 8 / 3;
    int h, w;
    const uint16_t *y = (const uint16_t*)pic->data[0];
    const uint16_t *u = (const uint16_t*)pic->data[1];
    const uint16_t *v = (const uint16_t*)pic->data[2];
    uint8_t *p = buf;
    uint8_t *pdst = buf;

    if (buf_size < aligned_width * avctx->height * 8 / 3) {
        av_log(avctx, AV_LOG_ERROR, "output buffer too small\n");
        return -1;
    }

#define CLIP(v) av_clip(v, 4, 1019)

#define WRITE_PIXELS(a, b, c)           \
    do {                                \
        val =   CLIP(*a++);             \
        val |= (CLIP(*b++) << 10) |     \
               (CLIP(*c++) << 20);      \
        bytestream_put_le32(&p, val);   \
    } while (0)

    for (h = 0; h < avctx->height; h++) {
        uint32_t val;
        for (w = 0; w < avctx->width - 5; w += 6) {
            WRITE_PIXELS(u, y, v);
            WRITE_PIXELS(y, u, y);
            WRITE_PIXELS(v, y, u);
            WRITE_PIXELS(y, v, y);
        }
        if (w < avctx->width - 1) {
            WRITE_PIXELS(u, y, v);

            val = CLIP(*y++);
            if (w == avctx->width - 2)
                bytestream_put_le32(&p, val);
        }
        if (w < avctx->width - 3) {
            val |= (CLIP(*u++) << 10) | (CLIP(*y++) << 20);
            bytestream_put_le32(&p, val);

            val = CLIP(*v++) | (CLIP(*y++) << 10);
            bytestream_put_le32(&p, val);
        }

        pdst += stride;
        memset(p, 0, pdst - p);
        p = pdst;
        y += pic->linesize[0] / 2 - avctx->width;
        u += pic->linesize[1] / 2 - avctx->width / 2;
        v += pic->linesize[2] / 2 - avctx->width / 2;
    }

    return p - buf;
}