[mythtv] devel/rtp: multiple IPTV streams, same port-no

Kevin Kuphal kkuphal at gmail.com
Mon Apr 30 15:13:05 UTC 2012

On Sun, Apr 29, 2012 at 6:46 AM, Niels Ole Kirkeby <nok at kirkeby.nu> wrote:

> 2012/4/28 Niels Ole Kirkeby <nok at kirkeby.nu>
>> Hi
>> I was trying to figure out why devel/rtp didn't work for me and found a
>> major (if you're struck by it) flaw in the multicast handling in MythTV.
>> The problem is that my provider delivers streams like
>> udp://222.111.222.xx:2000. That is for all streams the port-no is the same.
>> In Linux, basically only the port-no differentiates the various
>> udp-streams. Thus I noticed a strange phenomena in MythTV: two iptv-tuners
>> recording two different streams but all data goes to the first stream !
>> I made a small test-program: Open two sockets, join two different
>> multicast streams (udp:// and udp://
>> I noticed the bind() for the second socket
>> failed. When I read from the sockets, only the first socket has any data
>> but the data was a merge from both streams ! After some digging I found out
>> that apparently you can only have one common socket for all streams and
>> should use sockopt IP_PKTINFO to find the multicast group the data is for.
>> I'm not quite into the class-relations in MythTV yet but are trying to
>> figure out how to handle this. Could anybody responsible for the devel/rtp
>> branch please comment on this ? Whether this is "just" a patch or a major
>> rewrite ?
>> What's strikes me is that appearently I only had minor problems whether
>> the "old" IPTV code and that code didn't use IP_PKTINFO either.
> I just discovered another "hidden" feature of Linux: You can bind to a
> multicast address. Thus if the bind() call in iptvstreamhandler.cpp, line
> 211 includes the multicast adress instead in ANY_HOST it actually works.
> Just tested. However as far as I can understand, using IP_PKTINFO is the
> "portable" way to do, for those OS who understands this option. But since
> mythtv currently is only Linux, does it matter ?

MythTV runs on Linux, MacOS, and Windows so it does...

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