avformat/srtdec: speed up probing

libavformat/srtdec.c

@@ -43,6 +43,7 @@ static int srt_probe(AVProbeData *p)
         if (ff_subtitles_read_line(&tr, buf, sizeof(buf)) < 0)
             break;
         if ((num == i || num + 1 == i)
+            && buf[0] >= '0' && buf[1] <= '9' && strstr(buf, " --> ")
             && sscanf(buf, "%*d:%*2d:%*2d%*1[,.]%*3d --> %*d:%*2d:%*2d%*1[,.]%3d", &v) == 1)
             return AVPROBE_SCORE_MAX;
         num = atoi(buf);