[mythtv-users] Client-Server hardware arch questions?

[Isaac Richards]

On Tuesday 13 May 2003 12:45 pm, Max wrote:
> So here are the questions:
>
> * How does the Myth frontend talk to backend? Is the video (audio, still
> picture, etc) transmitted in-band or do I need to NFS export the directory
> containing the common files? Is the media stream using TCP or UDP?

You can do both, actually.  The backend will stream the file on the fly to the 
frontend for playback using TCP, but if you NFS mount the the recording 
directories so they're in the same place on the frontends as they are on the 
backend, it'll use that instead.  Currently, only TV recordings are 
frontend/backend aware, but I hope to change that sometime after the next 
release.

> * What are the bandwidth requirements for connecting FE to BE? My
> calculations using 2GB per hour as top end PVR250 recording puts it at
> about 5 Mbit/s sustained w/o overhead(which pretty much excludes 802.11b,
> but a/g or FastEthernet may work) Are these numbers anywhere near reality?

Yeah, that's close.  4GB/hour, though, for top end PVR250 recording.

> * I assume the decoding is done on the front end, are there any hardware
> MPEG accellerators that can be used to offload decoding on the front end? I
> mean something a bit more lightweight than PVR250 (which is what I have
> now) - I only need to decode, not encode. Would the old DVD MPEG cards
> work? Any of them supported under linux?

My p3-550 decodes full-resolution (720x480) files produced by the pvr-250 just 
fine, so you may not even need/want a hardware decoder.  The major issue of 
using those cards is that you need to have _everything_ shown be in mpeg 
format -- including the non-video user interfaces.

> * When you have multiple backends, do they communicate to determine optimal
> recording capabilities? Can you set priorities for recuring recordings to
> auto-determine what is recorded in case of conflict?

One backend is designated the 'master' and tells all the other ones what to 
record.  You can't set priorities, no, but you can tell it what you prefer to 
record in case of a conflict.  A couple people have mentioned they may work 
on implementing actual recording priorities, though.

> * When you have multiple backends, are they seen as one by the frontend?

Yup.  All communication from the frontend(s) goes to the master backend.

> * Where do the "plugins" run? On the backend? frontend? both?

Frontend.

> * How many frontends can a backend support?

No idea.  Most I've ever run simultaneously with off of a single backend was 3 
(2 live-tv sessions, one pre-recorded playback).  I don't believe there's any 
hard limit in the code.

> * Is there a possibility of (imaginary right now) "MythDVD" plugin allowing
> DVD playback running on frontend only?

With the DVD drive on the frontend?  Sure, that's easy -- you can add a button 
to the main frontend menu that starts up a dvd player app, or you can add a 
link in mythvideo to do the same.

Isaac