lavf: dont try to find fps for attached pictures

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

libavformat/utils.c

@@ -2769,6 +2769,8 @@ int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
                 fps_analyze_framecount *= 2;
             if (ic->fps_probe_size >= 0)
                 fps_analyze_framecount = ic->fps_probe_size;
+            if (st->disposition & AV_DISPOSITION_ATTACHED_PIC)
+                fps_analyze_framecount = 0;
             /* variable fps and no guess at the real fps */
             if(   tb_unreliable(st->codec) && !(st->r_frame_rate.num && st->avg_frame_rate.num)
                && st->info->duration_count < fps_analyze_framecount