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

Florian Lohoff flo at rfc822.org
Thu Apr 6 21:19:09 CEST 2006

On Thu, Apr 06, 2006 at 07:51:12PM +0200, Derk-Jan Hartman wrote:
> On 6-apr-2006, at 17:51, Florian Lohoff wrote:
> >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.
> Did you read the RFCs ?

When you mean reading like reading in a book then No. By looking up
the relations between the protocols and protocol numbers Yes. RFC2327
RFC3550 come to my mind having open most of the time. But you seem to
have something more specific on your mind - probably willing to share ?

> >My first guess from looking at the source seems to be that VLC is not
> >capable of doing RTP/RTCP for RTP/AVP 33.
> It was built for it.

Okay - i cant find any reference to RTCP in the code except the live.com
module. As module/access/udp.c is the one trying to bind to the port/ip
address in the SAP/SDP and complaining about the servers address not
beeing a local address and beeing able to bind to i would expect to see
RTCP mentioned there. It isnt but RTP is. So my assumption was that VLC
tries to handle RTP/AVP 33 itself but failing to see the connection
point not beeing a multicast address and even missing RTCP code for
handling this.

> VLC assumes that any SAP originated SDP announce of a MPEG-TS stream  
> is multicast, yes. it being unicast is also very uncommon.

It beeing uncommon i see. It beeing impossible or against any standard/rfc
i couldnt find. It would solve my problem with old Cat5500 not beeing
able to handle multicast traffic as good (Not beeing able to handle
multilayer multiprotocol switching concerning multicast, forwarding all
mcast traffic the route-switch engine and overflowing the 100MBit/s link
between layer 2 and layer 3 engine).

> Use --no-sap-preparse (or something) to avoid this behaviour.

Could you specify the "or something" ?

vlc --help --advanced --longhelp | egrep "sap|pre|parse"
VLC media player 0.8.4 Janus
            and that overrides previous settings.
      --sap-flow-control, --no-sap-flow-control
      --sap-interval <integer>   SAP announcement interval
      --key-prev <integer>       Previous
      --key-title-prev <integer> Select previous DVD title
      --key-chapter-prev <integer>
                                 Select prev DVD chapter
                                 Select prev DVD chapter

I see a ChangeLog entry mentioning "--sap-parse" but giving that 
doesnt change anything.

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