Allow muxing h264 into ts with startcode "001" instead of "0001".

Fixes ticket #2220.
Fixes ticket #4324.

libavformat/mpegtsenc.c

@@ -1203,7 +1203,7 @@ static void mpegts_write_pes(AVFormatContext *s, AVStream *st,
 
 int ff_check_h264_startcode(AVFormatContext *s, const AVStream *st, const AVPacket *pkt)
 {
-    if (pkt->size < 5 || AV_RB32(pkt->data) != 0x0000001) {
+    if (pkt->size < 5 || AV_RB32(pkt->data) != 0x0000001 && AV_RB24(pkt->data) != 0x000001) {
         if (!st->nb_frames) {
             av_log(s, AV_LOG_ERROR, "H.264 bitstream malformed, "
                    "no startcode found, use the video bitstream filter 'h264_mp4toannexb' to fix it "