[vlc-devel] Unicast RTP/RTCP - SDP RTP/AVP 33

Florian Lohoff flo at rfc822.org
Thu Apr 6 17:51:41 CEST 2006


Hi,
i wrote a little streaming server myself which is capable of doing
UDP or UDP/RTP Unicast/Multicast. Now as we have some Multicast
difficulties concerning bandwidth i tried to go the path of sending
SAP/SDP multicast and the datastream unicast via RTP/RTCP. I am
streaming MPEG2-TS directly from an DVB source. 

The problem now is that VLC seems to be unable to accept the SDP packet.
My first guess from looking at the source seems to be that VLC is not
capable of doing RTP/RTCP for RTP/AVP 33.

This is a SAP packet i am sending out:

sap_send: Sent SAP pkt
0000 20 00 6d d2 e0 02 7f fe 76 3d 30 0d 0a 73 3d 50     .m.....v=0..s=P
0010 68 6f 65 6e 69 78 0d 0a 74 3d 30 20 30 0d 0a 61    hoenix..t=0 0..a
0020 3d 74 6f 6f 6c 3a 67 65 74 73 74 72 65 61 6d 0d    =tool:getstream.
0030 0a 61 3d 74 79 70 65 3a 62 72 6f 61 64 63 61 73    .a=type:broadcas
0040 74 0d 0a 6f 3d 2d 20 36 64 64 32 20 31 31 34 34    t..o=- 6dd2 1144
0050 33 33 31 31 38 39 20 49 4e 20 49 50 34 20 73 74    331189 IN IP4 st
0060 72 65 61 6d 32 0d 0a 6d 3d 76 69 64 65 6f 20 33    ream2..m=video 3
0070 30 30 30 20 52 54 50 2f 41 56 50 20 33 33 0d 0a    000 RTP/AVP 33..
0080 63 3d 49 4e 20 49 50 34 20 73 74 72 65 61 6d 32    c=IN IP4 stream2
0090 2f 31 35 0d 0a                                     /15..

It shows up in the VLC Playlist - Double clicking leads to:

[00000277] access_udp access error: cannot open socket
[00000275] main input error: no suitable access module for `rtp://@stream2:3000'

Which is obviously correct - Stracing shows VLC trying to bind to the
ip address of stream2 as it assumes multicast traffic:

31527 socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 22
31527 setsockopt(22, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
31527 setsockopt(22, SOL_SOCKET, SO_RCVBUF, [524288], 4) = 0
31527 setsockopt(22, SOL_SOCKET, SO_SNDBUF, [524288], 4) = 0
31527 bind(22, {sa_family=AF_INET, sin_port=htons(3000), sin_addr=inet_addr("195.71.4.177")},
16) = -1 EADDRNOTAVAIL (Cannot assign requested address)
31527 close(22)                         = 0
31527 write(2, "[00000277] access_udp access err"..., 55 <unfinished ...>

Switching the RTP/AVP from 33 MP2T to 31 H261 sends the control to the LIVE.COM
lib which is happy to send out an RTCP RR Packet and gets a stream. (Which is
obviously the wrong encoding and thus nothing happens)

Flo
-- 
Florian Lohoff                  flo at rfc822.org             +49-171-2280134
                        Heisenberg may have been here.
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