ffmpeg: trivial simplification

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

ffmpeg.c

@@ -1730,7 +1730,7 @@ static int output_packet(InputStream *ist, const AVPacket *pkt)
     if (pkt->dts != AV_NOPTS_VALUE) {
         ist->next_dts = ist->dts = av_rescale_q(pkt->dts, ist->st->time_base, AV_TIME_BASE_Q);
         if (ist->st->codec->codec_type != AVMEDIA_TYPE_VIDEO || !ist->decoding_needed)
-            ist->next_pts = ist->pts = av_rescale_q(pkt->dts, ist->st->time_base, AV_TIME_BASE_Q);
+            ist->next_pts = ist->pts = ist->dts;
     }
 
     // while we have more to decode or while the decoder did output something on EOF