/* Are we at the start of a block? */
if (!cur_frame)
ret = avcodec_decode_video2(s->avctx, mjpeg_data, &s->mjpeg_data_size, avpkt);
+ else if (!s->mjpeg_data_size)
+ return AVERROR(EINVAL);
desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
if (desc && mjpeg_data->height % (s->frames_per_jpeg << desc->log2_chroma_h)) {