[mythtv-users] Assorted questions from a new user

Chris Thompson ct-myth at cthompson.com
Wed Mar 24 13:47:17 EST 2004

Matt R. (mattr at erols.com) wrote:
> I'm a ReplayTV 4000 series user, so I come to the table with that 
> paradigm.  I am a bit confused by the purpose of the seperable frontend 
> and backend.
> 1. Is this supposed to allow the set-top boxes to be tiny, 
> nearly-diskless terminals?
> 1.b. Do the frontend boxes merely stream content from the backend?
> 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... ?
> 3. If video content streams from the backend box to the set-top 
> frontends (live), what sort of LAN speeds are required?
> 4. Where does the other content (games, videos, mp3s) live?
> 4.b. Which cpu actually runs a game process?  Does the game executable 
> copy to the frontend box before executing locally?

My personal setup is as follows.

Backend box in the basement running an Athlon 1600, 512megs Ram and a 30gig
drive for the OS with a 160gig drive formatted with XFS instead of ext3
mounted as a file store. Fedora Core 1 installed per Jarod's howto and
running an NFS server.

Three capture cards in the backend, a PVR250 and two Aver M179s. These are
fed by three RCA DirecTV boxes. My DirecTV splitter is mounted on the wall
above the computer shelf in my utility room in the basement.

Three serial ports on the backend connect over home built serial cables for
channel changing.

My first of three frontends is a Chaintech 7NIF2 board in an Antec Minuet
case. Small, Home Theatoer looking. The motherboard is nForce2 with onboard
GeForce 4MX, SVideo out, LAN and sound, though no SPIDF or other sound
output for full home theater experience. I havent solved that part yet.

The frontend box lives under my television. It's an Athlon Barton 2500+
with 256megs of ram, a Sony silver faced DVD-ROM that matches the case and
a 10gig drive running Fedora Core 1.

The frontend mounts the backend box over NFS over standard 100meg ethernet.

Mythfrontend runs, connects to the mysql database for it's config, and, if
I select LiveTV, signals the backend to start writing a video file to the 
160gig drive in the mythtv/livetv directory in what you'd call a RingBuffer. 

Once that starts, the front end begins playing that file over NFS. There is, I
assume, some limit to the size of that ring buffer, though I've not
explored it. So it's not "STREAMING" in the way you'd normally think, it's
simply one machine writing down a file and the other reading it over NFS,
with the writer always staying ahead of the reader.

If I change channels on the front end, it signals the back end to fire off
a note to the DirecTV box over Serial, it clears the ringbuffer and starts
the process anew.

I could easily have done this setup with a card and a directv box under
each TV, but I have no coax run to either of my second and third TVs, and
I'd rather run just ethernet than ether and coax. In my setup, I keep all
the noise and mayhem on a shelf in my basement next to the furnace. When I
get my frontends diskless (see below) I'll be even happier.

My goals for this project are a few enhancements.

I'm keeping an eye out for super deals on 250gig drives. My goal is to
build a proper fileserver with RAID5 to act as my whole house server, not
just big space for myth. This will likely be a separate box, so my backend
would then read video from the capture cards and write it to the fileserver
over NFS.

I need two more front ends, one for the living room, and one for the
bedroom. Both of these will probably be largely identical to the one I've
got now.

I want to add a fourth capture card, and a fourth DirecTV box, as I want to
have one more tuner than I have TVs.

I want to make my frontend diskless. I've done considerable work in this
area, but right now am not really satisfied with the stability of it. If
you have an EPIA based front end, the MiniMyth distribution is intended to
diskless boot. Going diskless in my frontends will reduce power, heat and
noise, as well as remove any issues with a frontend system powering off

Chris Thompson

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