ffmpeg: fix the used maximum dts in the monotone dts workaround

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

ffmpeg.c

@@ -625,10 +625,10 @@ static void write_frame(AVFormatContext *s, AVPacket *pkt, OutputStream *ost)
         }
         av_log(NULL, AV_LOG_WARNING, "changing to %"PRId64". This may result "
                "in incorrect timestamps in the output file.\n",
-               ost->last_mux_dts + 1);
-        pkt->dts = ost->last_mux_dts + 1;
+               max);
+        pkt->dts = max;
         if (pkt->pts != AV_NOPTS_VALUE)
-            pkt->pts = FFMAX(pkt->pts, pkt->dts);
+            pkt->pts = FFMAX(pkt->pts, max);
       }
     }
     ost->last_mux_dts = pkt->dts;