ffmpeg: check pts like dts for being in the past.

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

ffmpeg.c

@@ -3129,7 +3129,8 @@ static int transcode(OutputFile *output_files, int nb_output_files,
                     int64_t pkt_pts = av_rescale_q(pkt.pts, ist->st->time_base, AV_TIME_BASE_Q);
                     delta   = pkt_pts - ist->next_dts;
                     if ( delta < -1LL*dts_error_threshold*AV_TIME_BASE ||
-                        (delta > 1LL*dts_error_threshold*AV_TIME_BASE && ist->st->codec->codec_type != AVMEDIA_TYPE_SUBTITLE)) {
+                        (delta > 1LL*dts_error_threshold*AV_TIME_BASE && ist->st->codec->codec_type != AVMEDIA_TYPE_SUBTITLE) ||
+                        pkt_pts+1<ist->pts) {
                         av_log(NULL, AV_LOG_WARNING, "PTS %"PRId64", next:%"PRId64" invalid droping st:%d\n", pkt.pts, ist->next_dts, pkt.stream_index);
                         pkt.pts = AV_NOPTS_VALUE;
                     }