static int mjpega_dump_header(AVBitStreamFilterContext *bsfc, AVCodecContext *avctx, const char *args,
                              uint8_t **poutbuf, int *poutbuf_size,
                              const uint8_t *buf, int buf_size, int keyframe)
{
    uint8_t *poutbufp;
    unsigned dqt = 0, dht = 0, sof0 = 0;
    int i;

    if (avctx->codec_id != AV_CODEC_ID_MJPEG) {
        av_log(avctx, AV_LOG_ERROR, "mjpega bitstream filter only applies to mjpeg codec\n");
        return 0;
    }

    *poutbuf_size = 0;
    *poutbuf = av_malloc(buf_size + 44 + FF_INPUT_BUFFER_PADDING_SIZE);
    poutbufp = *poutbuf;
    bytestream_put_byte(&poutbufp, 0xff);
    bytestream_put_byte(&poutbufp, SOI);
    bytestream_put_byte(&poutbufp, 0xff);
    bytestream_put_byte(&poutbufp, APP1);
    bytestream_put_be16(&poutbufp, 42); /* size */
    bytestream_put_be32(&poutbufp, 0);
    bytestream_put_buffer(&poutbufp, "mjpg", 4);
    bytestream_put_be32(&poutbufp, buf_size + 44); /* field size */
    bytestream_put_be32(&poutbufp, buf_size + 44); /* pad field size */
    bytestream_put_be32(&poutbufp, 0);             /* next ptr */

    for (i = 0; i < buf_size - 1; i++) {
        if (buf[i] == 0xff) {
            switch (buf[i + 1]) {
            case DQT:  dqt  = i + 46; break;
            case DHT:  dht  = i + 46; break;
            case SOF0: sof0 = i + 46; break;
            case SOS:
                bytestream_put_be32(&poutbufp, dqt); /* quant off */
                bytestream_put_be32(&poutbufp, dht); /* huff off */
                bytestream_put_be32(&poutbufp, sof0); /* image off */
                bytestream_put_be32(&poutbufp, i + 46); /* scan off */
                bytestream_put_be32(&poutbufp, i + 46 + AV_RB16(buf + i + 2)); /* data off */
                bytestream_put_buffer(&poutbufp, buf + 2, buf_size - 2); /* skip already written SOI */
                *poutbuf_size = poutbufp - *poutbuf;
                return 1;
            case APP1:
                if (i + 8 < buf_size && AV_RL32(buf + i + 8) == AV_RL32("mjpg")) {
                    av_log(avctx, AV_LOG_ERROR, "bitstream already formatted\n");
                    memcpy(*poutbuf, buf, buf_size);
                    *poutbuf_size = buf_size;
                    return 1;
                }
            }
        }
    }
    av_freep(poutbuf);
    av_log(avctx, AV_LOG_ERROR, "could not find SOS marker in bitstream\n");
    return 0;
}