#8474: rtcpport param doesn't add a=rtcp to SDP
----------------------------------+----------------------------------
             Reporter:  juannm    |                     Type:  defect
               Status:  new       |                 Priority:  normal
            Component:  ffmpeg    |                  Version:  4.2
             Keywords:  rtp, sdp  |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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 Summary of the bug:
 It is possible to specify an RTCP port that is not the default RTP + 1.
 For this, we just have to add the parameter "rtcpport" to the output URL:

 {{{
 rtp://127.0.0.1:5004?rtcpport=54321
 }}}

 However, FFmpeg is not adding the corresponding media-level attribute
 "a=rtcp:54321" to the generated SDP file.

 This seems like a bug to me instead of a missing feature, because in SDP,
 the omission of the "a=rtcp" attribute is nominally equivalent to an
 implicit presence of that attribute, where the value is RTP + 1.

 So, in short, FFmpeg is generating an SDP where the RTCP port is wrong.



 How to reproduce:
 {{{
 ffmpeg \
     -re \
     -i video.mp4 \
     -an \
     -c:v copy \
     -f rtp \
     -sdp_file video.sdp \
     "rtp://127.0.0.1:5004?rtcpport=54321"
 }}}

 generates an SDP file, "video.sdp", with these contents:

 {{{
 SDP:
 v=0
 o=- 0 0 IN IP4 127.0.0.1
 s=No Name
 c=IN IP4 127.0.0.1
 t=0 0
 a=tool:libavformat 58.29.100
 m=video 5004 RTP/AVP 96
 a=rtpmap:96 H264/90000
 a=fmtp:96 packetization-mode=1; sprop-parameter-
 sets=Z0LAH9kAUAW7ARAAAD6QAAu4CPGDJIA=,aMuMsg==; profile-level-id=42C01F
 }}}

 Expected SDP would NOT have the invalid first line "SDP:" (that's a
 different bug: #7068), and also it would have the "a=rtcp" line:

 {{{
 v=0
 o=- 0 0 IN IP4 127.0.0.1
 s=No Name
 c=IN IP4 127.0.0.1
 t=0 0
 a=tool:libavformat 58.29.100
 m=video 5004 RTP/AVP 96
 a=rtcp:54321
 a=rtpmap:96 H264/90000
 a=fmtp:96 packetization-mode=1; sprop-parameter-
 sets=Z0LAH9kAUAW7ARAAAD6QAAu4CPGDJIA=,aMuMsg==; profile-level-id=42C01F
 }}}

 Full, uncut console output generated with '-report' and provided in the
 attached file.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/8474>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker
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