ff_choose_timebase: only try factors upto 14

otherwise a unexpected timebase could be choosen
that is one that is thousand times more precisse than requested
which can have sideeffects.
Signed-off-by: NMichael Niedermayer <michaelni@gmx.at>

libavformat/mux.c

@@ -113,7 +113,7 @@ AVRational ff_choose_timebase(AVFormatContext *s, AVStream *st, int min_precissi
     } else {
         q = st->codec->time_base;
     }
-    for (j=2; j<2000; j+= 1+(j>2))
+    for (j=2; j<14; j+= 1+(j>2))
         while (q.den / q.num < min_precission && q.num % j == 0)
             q.num /= j;
     while (q.den / q.num < min_precission && q.den < (1<<24))