Better threshold for the gcd based r_frame_rate calculation.

Fixes Gilmore Girls_Net 5_2011_01_08_16_10_53.wtv and RTL GP- WK Superbike - Qatar_RTL7_2009_03_14_15_49_23.wtv.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/utils.c

@@ -2404,7 +2404,7 @@ int av_find_stream_info(AVFormatContext *ic)
             // the check for tb_unreliable() is not completely correct, since this is not about handling
             // a unreliable/inexact time base, but a time base that is finer than necessary, as e.g.
             // ipmovie.c produces.
-            if (tb_unreliable(st->codec) && st->info->duration_count > 15 && st->info->duration_gcd > 1 && !st->r_frame_rate.num)
+            if (tb_unreliable(st->codec) && st->info->duration_count > 15 && st->info->duration_gcd > FFMAX(1, st->time_base.den/(500LL*st->time_base.num)) && !st->r_frame_rate.num)
                 av_reduce(&st->r_frame_rate.num, &st->r_frame_rate.den, st->time_base.den, st->time_base.num * st->info->duration_gcd, INT_MAX);
             if (st->info->duration_count && !st->r_frame_rate.num
                && tb_unreliable(st->codec) /*&&