utils: consider mpeg4 in mp4/mov to have a unreliable timebase

Partly fixes Ticket1664
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/utils.c

@@ -2475,6 +2475,7 @@ static int tb_unreliable(AVCodecContext *c){
        || c->time_base.den <    5L*c->time_base.num
 /*       || c->codec_tag == AV_RL32("DIVX")
        || c->codec_tag == AV_RL32("XVID")*/
+       || c->codec_tag == AV_RL32("mp4v")
        || c->codec_id == AV_CODEC_ID_MPEG2VIDEO
        || c->codec_id == AV_CODEC_ID_H264
        )