ffplay ignores a=rtcp SDP attribute for RTP streams

[Juan Navarro]

Summary of the bug:

When sending RTP with ffmpeg, 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. For example:

ffmpeg -re -i video.mp4 -an -c:v copy -f rtp -sdp_file video.sdp \
    "rtp://192.168.1.109:5004?rtcpport=54321"

To play back this stream, ffplay can be used with an SDP file. The equivalent of "rtcpport=54321" in SDP format is an attribute such as "a=rtcp:54321", like in this example SDP (generated by ffmpeg and edited by hand to work around related bugs ​https://trac.ffmpeg.org/ticket/7068 and ​https://trac.ffmpeg.org/ticket/8474):

v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 192.168.1.109
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

However, ffplay ignores the "a=rtcp" attribute, thus it listens for RTCP packets in the default port 5005 (RTP + 1), and packets sent by ffmpeg don't arrive correctly to their destination.

Example playback command:

ffplay \
    -protocol_whitelist file,rtp,udp \
    -i video.sdp

This renders the usage of "rtcpport" URL parameter not viable if all we use is FFmpeg itself for both sending and receiving.

Full, uncut console outputs from ffmpeg and ffplay generated with '-report' and provided in the attached files.

Related bugs:

• ffmpeg SDP file generation: incorrect header (​https://trac.ffmpeg.org/ticket/7068)
• rtcpport param doesn't add a=rtcp to SDP (​https://trac.ffmpeg.org/ticket/8474)

[Juan Navarro]

ffmpeg comand (RTP sender)

[Juan Navarro]

ffplay comand (RTP receiver)

[Carl Eugen Hoyos]

Is this issue reproducible with current FFmpeg git head?

[Balling]

Patch here ​https://patchwork.ffmpeg.org/project/ffmpeg/patch/20200202034831.26072-1-junli1026@gmail.com/

[xiaofeng]

The patch does not work with the multicast case.