[mythtv-users] Assorted questions from a new user

Bruce Markey bjm at lvcm.com
Mon Mar 22 14:09:23 EST 2004

Matt R. wrote:
> Dear everyone,
> Thanks in advance for any replies.  I've struggled with trying to answer 
> these questions for quite some time now.  I'm sorry if they're all 
> rather dumb questions.  My only defense is that I _HAVE_ been reading 
> through the documentation and the mailing list archives for over a week 
> now, but these questions remain unanswered.
> Fundamental Questions:
> I'm a ReplayTV 4000 series user,

Well then, welcome to a world where there is a list of upcoming
recordings, recordings don't disappear when the rule that recorded
it is removed, previously recorded episodes are remembered long
after the recording is deleted, disk space isn't used up by pre-
allocation, your priorities can be expressed without having to
make cryptic choices to satisfy an algorithm described on page 42
of the manual, etc., etc., etc. ;-).

> so I come to the table with that 
> paradigm.  I am a bit confused by the purpose of the seperable frontend 
> and backend.

The backend controls tuner cards and is used for recording.
It has no GUI and is needed on each machine that has one or
more TV cards but is not needed on any machine that does not
have a tuner.

There is exactly one master backend that runs the scheduler
and assigns recording tasks to other backends (if any) which
are called slave backends. Backend are normally running all
the time so they are ready to record and available to serve
any files they have recorded.

The frontend is the GUI that users use for playback. It can
run on a computer monitor or on a TV if the computer has a
graphics card that supports TV-out. A mythbackend may or may
not also run on the same machine depending on if the system
has a TV card. Any frontend can be stopped or started at any
time with no impact on the recording schedule.

There is no master or slave frontend but frontends are often
referred to as local or remote indicating whether or not they
are on the same machine that holds recorded files. Any frontend
can play files recorded by any of the backends.

> 1. Is this supposed to allow the set-top boxes to be tiny, 
> nearly-diskless terminals?

Not really but it does make that possible. The split is
so that so that GUIs and recorders can be mixed and matched
in a client-server sort of way.

> 1.b. Do the frontend boxes merely stream content from the backend?

Merely? ;-). The frontend process is the GUI and it can read local
files or stream from a remote backend. From a user perspective,
you only have a list of all recordings and shouldn't know or
care where the file was recorded (or is currently recording).
For any frontend on your network you will see the same list and
can play any recording on any machine.

> 2. Is it customary for each set-top box to be both a frontend and a 
> backend? (i.e., the ReplayTV 4000 approach)


> 2.b. Is it wise... ?

Yes. Where ever there is a TV and you are adding a computer
for mythfrontend, there will presumably be an active cable
drop. You might as well have a tuner card also to take full

> 3. If video content streams from the backend box to the set-top 
> frontends (live), what sort of LAN speeds are required?

3.6GB/hour (overkill ;-) = 1MB/second. 2GB/hour is more than
enough for good quality and should work over 10mbit ethernet.
802.11b is possible if you lower the bitrate enough but you can
still get a very watchable picture. 802.11g and certainly 
100mbit are more than adequate.

--  bjm

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