[mythtv-users] Way out idea on watching same thing in multiplerooms

Greg Oliver oliver.greg at gmail.com
Tue Jan 5 03:05:55 UTC 2010


On Mon, Jan 4, 2010 at 7:52 PM, Tortise <tortise at paradise.net.nz> wrote:
> ----- Original Message ----- From: "Greg Oliver" <oliver.greg at gmail.com>
> To: "Discussion about mythtv" <mythtv-users at mythtv.org>
> Sent: Tuesday, January 05, 2010 2:26 PM
> Subject: Re: [mythtv-users] Way out idea on watching same thing in
> multiplerooms
>
>
>> Without broadcast quality hardware, there will be no synchronization..
>
> Period..  And even then, certain architectures must be met..  You
> cannot have motherboard-x, videocard-y, nic-z and expect to accomplish
> *exactly* synchronized video...  Everyone is kicking a dead horse
> trying to prove how smart we are..  He simply wanted to know the best
> way to watch the same stuff across frontends..  Multicast is the
> obviously best and only answer to accomplish it for free.  It may not
> be to atomic clock precision, but it will have to work...  I would
> assume a script could easily be written to listen for IGMP events, and
> play them with an external player that supports multicast..  I am not
> too sure if there is something in the database that would require
> updating prior, such as the IGMP group to join, etc, but it is not far
> fetched and would not really require mythtv to be patched for
> multicast support..
>
>
> Thanks Greg, I for one appreciate your reading of it all.
>
> I've just played a DVD multicast using the DVD player setting as
>
> vlc file://%d
> :sout=#transcode{vcodec=h264,vb=800,scale=1,acodec=mp4a,ab=128,channels=2,samplerate=44100}:duplicate{dst=std{access=udp,mux=ts,dst=239.0.0.0:1234},dst=display}
> vlc://quit
>
> The  vlc://quit doesn't seem to work - it seems to time out when stopping
> playback.

Unfortunately, I have no experience with vlc..  We generally just
throw them out on the wire and let any player that supports streaming
play them..  As our servers are linux based, unfortunately I would say
that 99.99% of our clients run windows :(

> The DVD plays in a VLC window on the mythtv FE Server.  I imagine an
> additional switch will make it full screen.
>
> Using a VLC client on different machine (I used XP in this case) plays the
> same DVD (with a small acceptable start buffering difference) from
> udp://239.0.0.0:1234.

Multicast and buffering can get tricky since buffering implies that
there is adequate time to revover if packets are not received while
multicast basically says if you do not get the packets, do not expect
them, and do not ask for them - just move on..  A truly multicast
client should not buffer - other than to possibly correct for jerky
video due to missing packets.

> Each new client is each going to have much the same start buffering pause,
> so each client will be pretty close in sync with other clients, however the
> server does not have this buffering delay so will always be a little ahead.
>  For me that is quite acceptable (I'd prefer to see discussion how to move
> it forwards rather than why there is a small sync issue and that is a reason
> to not progress multicasting further...

Yes, the main drawback to multicast is that the first packet is always
unicast (or it should be).  Of course, you can always just throw
packets out on a multicast address and that will work in a non busy
multicast environment, but the necessity for the network hardware and
you PC to "gracefully" handle assignments is a must in a busy network.

> I would test "Watch Videos" also, if I could figure out how to get a source
> file in to the directory to play.(!)  (I copied a .mpg and .ts file in
> however the GUI stills says there are no files...  Hmmm)

You should check out ffserver - it transcodes and kicks out multicast
streams on request..  Or mpeg4ip - vlc users should be familiar with
it..

> Its a shame I cannot do the same with recordings (or even "Live" TV).

You could with scripts (maybe not livetv).. I am not familiar with
livetv enough to know the format and disk writes etc, to know how
reliable what was read from disk would be..  ringbuffer flushes,
etc...

> Still another positive step in the desired direction suggesting the concept
> works - and given this is relatively generic functionality it may not be far
> off progressing further.

Yeah, this is nothing new, but like someone said, the interest may not
be high since not many people would probably try to use it.  Our
company broadcasts to TV, phones, and PC for intercom and emergency
functionality mostly, but also some pretty nifty stuff that clients
want to do - or dream up...


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