avformat/utils: Preserve packet duration when parsing is done only for headers

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

libavformat/utils.c

@@ -1223,7 +1223,7 @@ static int parse_packet(AVFormatContext *s, AVPacket *pkt, int stream_index)
         }
 
         /* set the duration */
-        out_pkt.duration = 0;
+        out_pkt.duration = (st->parser->flags & PARSER_FLAG_COMPLETE_FRAMES) ? pkt->duration : 0;
         if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
             if (st->codec->sample_rate > 0) {
                 out_pkt.duration =