avformat: dont run update_initial_duration() twice

This should avoid floods of first_dts not matching debug messages
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avformat.h

@@ -893,6 +893,10 @@ typedef struct AVStream {
      */
     int pts_wrap_behavior;
 
+    /**
+     * Internal data to prevent doing update_initial_durations() twice
+     */
+    int update_initial_durations_done;
 } AVStream;
 
 AVRational av_stream_get_r_frame_rate(const AVStream *s);

libavformat/utils.c

@@ -998,6 +998,9 @@ static void update_initial_durations(AVFormatContext *s, AVStream *st,
     int64_t cur_dts= RELATIVE_TS_BASE;
 
     if(st->first_dts != AV_NOPTS_VALUE){
+        if (st->update_initial_durations_done)
+            return;
+        st->update_initial_durations_done = 1;
         cur_dts= st->first_dts;
         for(; pktl; pktl= get_next_pkt(s, st, pktl)){
             if(pktl->pkt.stream_index == stream_index){