warn user if video codec timebase is very high

Originally committed as revision 9232 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/movenc.c

@@ -1488,6 +1488,11 @@ static int mov_write_header(AVFormatContext *s)
             track->tag = mov_find_video_codec_tag(s, track);
             track->timescale = st->codec->time_base.den;
             av_set_pts_info(st, 64, 1, st->codec->time_base.den);
+            if (track->timescale > 100000)
+                av_log(NULL, AV_LOG_WARNING,
+                       "WARNING codec timebase is very high. If duration is too long,\n"
+                       "file may not be playable by quicktime. Specify a shorter timebase\n"
+                       "or choose different container.\n");
         }else if(st->codec->codec_type == CODEC_TYPE_AUDIO){
             track->tag = mov_find_audio_codec_tag(s, track);
             track->timescale = st->codec->sample_rate;