- srt_to_ass(avctx, &buffer, avpkt->data, x1, y1, x2, y2);
- ret = ff_ass_add_rect(sub, buffer.str, s->readorder++, 0, NULL, NULL);
+ ret = srt_to_ass(avctx, &buffer, avpkt->data, x1, y1, x2, y2);
+ if (ret >= 0)
+ ret = ff_ass_add_rect(sub, buffer.str, s->readorder++, 0, NULL, NULL);