The VideoLAN Forums

Posted: **19 Aug 2019 19:03**

Hello,

On what multicast IP and what port does the VLC listen for SAP?

I am sending periodically this SAP packet (please see screenshot below), however no success to get it shown in the VLC playlist@SAP.

The packet seems to be formed correctly - Wireshark seems to catch it and decode correctly. I am sending to 224.2.127.254 to port 9875 as per RFC2974. I don't know where to look for the mistake. Can you please help?

Thank you for any hints. (hopefully the image will display correctly)

Posted: **19 Aug 2019 20:13**

Code: Select all

udp        0      0 224.0.0.255:9875        0.0.0.0:*                          
udp        0      0 239.255.255.255:9875    0.0.0.0:*                          
udp        0      0 239.195.255.255:9875    0.0.0.0:*                          
udp        0      0 224.2.127.254:9875      0.0.0.0:*                          
udp6       0      0 ff02::2:7ffe:9875       :::*                               
udp6       0      0 ff02::2:7ffe:9875       :::*                               
udp6       0      0 ff04::2:7ffe:9875       :::*                               
udp6       0      0 ff05::2:7ffe:9875       :::*                               
udp6       0      0 ff06::2:7ffe:9875       :::*                               
udp6       0      0 ff07::2:7ffe:9875       :::*                               
udp6       0      0 ff08::2:7ffe:9875       :::*                               
udp6       0      0 ff09::2:7ffe:9875       :::*                               
udp6       0      0 ff0a::2:7ffe:9875       :::*                               
udp6       0      0 ff0b::2:7ffe:9875       :::*                               
udp6       0      0 ff0c::2:7ffe:9875       :::*                               
udp6       0      0 ff0d::2:7ffe:9875       :::*                               
udp6       0      0 ff0e::2:7ffe:9875       :::*

Posted: **19 Aug 2019 22:19**

Thank you for the table. So it indeed listens on the IP/port mentioned in the RFC, despite not showing my SAP announcement.

Is there a way to debug the SAP on the VLC side, too see if the VLC indeed receives these packets and the (possible) reason why VLC does ignore it (if it is received)? Is there any trace for this available?

Could anyone please check the sample SAP packet is built properly? (The UDP payload in HEX is below, if anyone interested)

Code: Select all

20 00 12 34   c0 a8 01 04   61 70 70 6c   69 63 61 74
69 6f 6e 2f   73 64 70 00   76 3d 30 0d   0a 73 3d 54   
65 73 74 20   53 65 73 73   69 6f 6e 0d   0a 63 3d 49
4e 20 49 50   34 20 32 33   39 2e 30 2e   30 2e 31 0d
0a 6d 3d 61   75 64 69 6f   20 35 30 30   34 20 52 54
50 2f 41 56   50 20 31 30   0d 0a

The SDP data file contains the following, \r\n used as a line end:

Code: Select all

v=0
s=Test Session
c=IN IP4 239.0.0.1
m=audio 5004 RTP/AVP 10

This short descriptor should be (is) enough for VLC to play a stream normally (without SAP announcement).

Posted: **19 Aug 2019 23:14**

Okay, never mind... just if I would look in the damn debug log file sooner. dammit!

So after tweaking the SDP a bit to not omit any mandatory SDP parameter, it still does not work.

I do have implemented all mandatory: v, o, s, t, m and c.

Code: Select all

v=0
o=- 0 0 IN IP4 192.168.1.4
s=Test Session
t=0 0
c=IN IP4 239.0.0.1
m=audio 5004 RTP/AVP 10

yet VLC still tells me "sap debug: missing SDP media description". Does not make sense. A correct "m" line is already present. What does VLC think is missing?

Posted: **19 Aug 2019 23:32**

Okay, finally with a bit of (mostly moral) help from a friend, I found a solution for the problem from previous post:

I had the SDP descriptor lines in this order: V O S T C M. --> VLC says missing media description.

If I swap the C and M, it works in this order correctly: V O S T M C.

It is probably quite brave to say that I have found a bug in VLC SDP parser now, but look, in RFC4566 there is this example of SDP:

Code: Select all

      v=0
      o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5
      s=SDP Seminar
      i=A Seminar on the session description protocol
      u=http://www.example.com/seminars/sdp.pdf
      e=j.doe@example.com (Jane Doe)
      c=IN IP4 224.2.17.12/127
      t=2873397496 2873404696
      a=recvonly
      m=audio 49170 RTP/AVP 0
      m=video 51372 RTP/AVP 99
      a=rtpmap:99 h263-1998/90000

clearly, C line is before M line. And it seems C before M is even a valid option.

Why does this order (V O S T C M) not work with VLC?

Posted: **20 Aug 2019 18:49**

It does not work because it is syntactically invalid.

Posted: **21 Aug 2019 01:22**

...which is what it seems it indeed is. :-/

It must either be V O S C T M ot V O S T M C order.

V O S T C M order is violating the specified order. Silly me have not read the RFC thoroughly enough and programming at well past midnight after a full work day shall be prohibited and sleep hours mandatory, as is the strong order of the SDP lines

Thanks for helping, it is currently working fine (until I'll break it somewhere again, sigh).

Posted: **19 Feb 2020 10:42**

Please share the complete vlc cli command to stream multicast with sap announcement.

Posted: **20 Feb 2020 04:55**

can any one share the cli format on how to streaming rtp multicast with SAP announcement ?

Posted: **20 Feb 2020 19:46**

Can you not hijack discussion threads?

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