X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=libavformat%2Frtpenc.c;h=7adf687c7f99461bd9cb7da3e6850513a510f2f8;hb=fc2922836bc289e443c0c7a20450bf8f03c0785d;hp=b7502704b16da3abd7459af4c5177e988919ec43;hpb=a0dbe2a58cf5c4c635df238e1d1f680120d5a6bc;p=ffmpeg

diff --git a/libavformat/rtpenc.c b/libavformat/rtpenc.c
index b7502704b16..7adf687c7f9 100644
--- a/libavformat/rtpenc.c
+++ b/libavformat/rtpenc.c
@@ -35,6 +35,7 @@ static const AVOption options[] = {
     { "payload_type", "Specify RTP payload type", offsetof(RTPMuxContext, payload_type), AV_OPT_TYPE_INT, {.i64 = -1 }, -1, 127, AV_OPT_FLAG_ENCODING_PARAM },
     { "ssrc", "Stream identifier", offsetof(RTPMuxContext, ssrc), AV_OPT_TYPE_INT, { .i64 = 0 }, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM },
     { "cname", "CNAME to include in RTCP SR packets", offsetof(RTPMuxContext, cname), AV_OPT_TYPE_STRING, { .str = NULL }, 0, 0, AV_OPT_FLAG_ENCODING_PARAM },
+    { "seq", "Starting sequence number", offsetof(RTPMuxContext, seq), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 65535, AV_OPT_FLAG_ENCODING_PARAM },
     { NULL },
 };
 
@@ -124,6 +125,16 @@ static int rtp_write_header(AVFormatContext *s1)
         /* Round the NTP time to whole milliseconds. */
         s->first_rtcp_ntp_time = (s1->start_time_realtime / 1000) * 1000 +
                                  NTP_OFFSET_US;
+    // Pick a random sequence start number, but in the lower end of the
+    // available range, so that any wraparound doesn't happen immediately.
+    // (Immediate wraparound would be an issue for SRTP.)
+    if (s->seq < 0) {
+        if (st->codec->flags & CODEC_FLAG_BITEXACT) {
+            s->seq = 0;
+        } else
+            s->seq = av_get_random_seed() & 0x0fff;
+    } else
+        s->seq &= 0xffff; // Use the given parameter, wrapped to the right interval
 
     if (s1->packet_size) {
         if (s1->pb->max_packet_size)
@@ -309,7 +320,7 @@ void ff_rtp_send_data(AVFormatContext *s1, const uint8_t *buf1, int len, int m)
     avio_write(s1->pb, buf1, len);
     avio_flush(s1->pb);
 
-    s->seq++;
+    s->seq = (s->seq + 1) & 0xffff;
     s->octet_count += len;
     s->packet_count++;
 }