rtpdec: unwrap RTP timestamps for PTS calculation

The timestamp field in RTPDemuxContext was unused before this.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/rtpdec.c

@@ -439,7 +439,13 @@ static void finalize_packet(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestam
 
     if (!s->base_timestamp)
         s->base_timestamp = timestamp;
-    pkt->pts = s->range_start_offset + timestamp - s->base_timestamp;
+    /* assume that the difference is INT32_MIN < x < INT32_MAX, but allow the first timestamp to exceed INT32_MAX */
+    if (!s->timestamp)
+        s->unwrapped_timestamp += timestamp;
+    else
+        s->unwrapped_timestamp += (int32_t)(timestamp - s->timestamp);
+    s->timestamp = timestamp;
+    pkt->pts = s->unwrapped_timestamp + s->range_start_offset - s->base_timestamp;
 }
 
 static int rtp_parse_packet_internal(RTPDemuxContext *s, AVPacket *pkt,

libavformat/rtpdec.h

@@ -151,6 +151,7 @@ struct RTPDemuxContext {
     uint32_t timestamp;
     uint32_t base_timestamp;
     uint32_t cur_timestamp;
+    int64_t  unwrapped_timestamp;
     int64_t  range_start_offset;
     int max_payload_size;
     struct MpegTSContext *ts;   /* only used for MP2T payloads */

libavformat/rtspdec.c

@@ -52,6 +52,8 @@ static int rtsp_read_play(AVFormatContext *s)
                 rtpctx->last_rtcp_ntp_time  = AV_NOPTS_VALUE;
                 rtpctx->first_rtcp_ntp_time = AV_NOPTS_VALUE;
                 rtpctx->base_timestamp      = 0;
+                rtpctx->timestamp           = 0;
+                rtpctx->unwrapped_timestamp = 0;
                 rtpctx->rtcp_ts_offset      = 0;
             }
         }