[mythtv] distributed master/slaves configuration questions

[Bruce Markey]

Michael J. Hammel wrote:
...
> I'd like to set this box up as a MythTV master backend server and then
> set up a series of MiniMyth slaves throughout the house (in the long
> term I'll have to migrate to a much bigger server, but this box will do
> for now).  My goal is to have the slaves tell the server when to record
> and what to feed to the slave - including live TV if possible.  I have
> some questions on if/how this might be done.

First, it appears that most of this message is based on some
confusion about what the frontend and backend do.

A frontend is run on a system where you have an X display and
what to see the GUI and watch recordings (LiveTV is a form of
recording that is stored in a temporary file then you play as
it records).

A backend controls the tuner(s) on a system and therefore is
only run on machines that actually have tuners. The master
backend has extra duties of managing the scheduler and such.

To clarify some terminology, "slave" refers to a remote backend
process. Remote frontends should not be referred to as "slaves".
 
> 1. I take it that slaves require a slave backend configured and that it
> is the backends that talk to one another to get the master to feed the
> slave the video/audio.  The frontend only talks to the local backend. 
> Is this a correct view of the architecture?  As long as the master
> backend is running (the master frontend does not have to be running),
> recordings requested by slaves will be made and LiveTV can be fed to
> slaves.  Correct?

Nope. A slave is only needed on a machine other than the master
which has a tuner. A remote frontend only machine does not need
a slave backend unless there is a tuner card on the machine. The
frontends always connect to the master backend. It is only after
the master tells the frontend that a slave has the recording that
it is looking for that the frontend connects to the slave backend.

> 2. The documentation suggests that part of the slave backend does not
> need to be run but it isn't clear on if a TV input (re: a TV or PVR
> card) is required.  Can a slave run without a hardware TV input directly
> in the slave system?

No tuner, no slave.

> 3. Can a slave with a TV card be configured to watch LiveTV directly
> from that card (without recording features)?  The reason this might be
> desirable is if the lag in a local network makes watching recorded
> LiveTV distracting then the user could switch to a more direct feed.

If there is a local tuner, it is chosen first for LiveTV. If
the local tuner is already busy then a remote tuner is used.
Ironically, there are so many busy threads with local LiveTV
that there is actually less jitter if the tuner is on another
machine.

> 4. What does a master do (and what does the slave front end show) when
> no video input sources are available for either recording or live TV?

If you go to live TV when all tuner are busy you get a message
to that effect that suggests you can go to Watch Recordings to
watch what is being recorded right now.

> 5. Can slaves access all of MythTVs add-ons via the master - for
> example, can games be fed to the slave to be run on the slave hardware
> and can photos (re: MythGallery) be viewed on the slave if they are
> stored on the server?  I know in the latter case you could set up NFS
> mounts, but I was wondering if there was a mechanism (either by design
> or already coded) that allows feeding the images via TCP to the slave
> for display?  This would be preferable to reduce admin overhead on the
> slaves.  

Each of the add-ons are different. Note that only TV has backends
and slave backend processes. Most of the add-ons are frontend
only.

> 6. Do recordings get streamed to the slaves or do the slaves have to
> pick them up via NFS mount points?  If the former, what protocol is
> being used for streaming?  RTSP?  Something simpler?

The frontend opens a control socket to the backend and another
socket to transfer and buffer data. The protocol is specific
to mythtv. If a prerecorded show is local (or appears as local
due to NFS), the frontend reads the file directly.

> I've got a couple of bugs to report.  Two are minor although I do need
> to track down a serious problem with stability when LiveTV is left
> running for extended periods.  This might be an ivtv problem, though the
> backend is segfaulting too.

http://www.mythtv.org/docs/mythtv-HOWTO-20.html#ss20.9

--  bjm