Reset pts_correction state on codec flush.

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

libavcodec/utils.c

@@ -1879,6 +1879,9 @@ void avcodec_flush_buffers(AVCodecContext *avctx)
         ff_thread_flush(avctx);
     else if(avctx->codec->flush)
         avctx->codec->flush(avctx);
+
+    avctx->pts_correction_last_pts =
+    avctx->pts_correction_last_dts = INT64_MIN;
 }
 
 static void video_free_buffers(AVCodecContext *s)