mpegts: prevent division by zero

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavformat/mpegts.c

@@ -2681,8 +2681,17 @@ static int mpegts_read_header(AVFormatContext *s)
                 packet_count[nb_pcrs] = nb_packets;
                 pcrs[nb_pcrs] = pcr_h * 300 + pcr_l;
                 nb_pcrs++;
-                if (nb_pcrs >= 2)
-                    break;
+                if (nb_pcrs >= 2) {
+                    if (pcrs[1] - pcrs[0] > 0) {
+                        /* the difference needs to be positive to make sense for bitrate computation */
+                        break;
+                    } else {
+                        av_log(ts->stream, AV_LOG_WARNING, "invalid pcr pair %"PRId64" >= %"PRId64"\n", pcrs[0], pcrs[1]);
+                        pcrs[0] = pcrs[1];
+                        packet_count[0] = packet_count[1];
+                        nb_pcrs--;
+                    }
+                }
             } else {
                 finished_reading_packet(s, ts->raw_packet_size);
             }