[mythtv-users] Good system design documentation?

Steve Tate srt at cs.unt.edu
Sat Jun 4 22:04:16 UTC 2005

On Fri, 3 Jun 2005, Michael T. Dean wrote:

> Steve Tate wrote:
>> Is there a document available that goes through the various components
>> of a mythtv system and talks about various system design tradeoffs?
> Not yet, but Robert Kulagowski is extremely good at incorporating 
> patches/changes/additions into the official documentation.  Perhaps once you 
> get the information you need, you can help improve the docs.

Thank you!  (and Mudit and Robert) for the comments.  I had seen the
Wiki, and I guess I'm just nervous about laying out cash for hardware
when I'm not entirely clear on how things work.  If I've got the time
later, after I figure thigns out, I'll take your advice and write
something up to "give back".

I've got the PVR-250 already, so decided to go ahead and put that in
an existing system, install the software, and play with it, even if
that's now how I'm going to do it in "production."  I do understand
things MUCH better after having played with it a little bit.

One curious question though, on this comment of yours:

>> (which is why I'd want the tuner in the frontend box in the first
>> place)?  And then I'd have problems using the remote control from the
>> PVR-250 as well...   I'd really like a RAM-based ringbuffer for live
>> TV, so that doesn't hit the network at all,
> You could do the same with a HDD-based ring buffer.

Not if my system doesn't have a HDD!  :-)

> Remember that MPEG-2 
> video will take up at least a GiB/hr, so you'd have to have a 512MB area of 
> memory dedicated to the LiveTV Ring Buffer (i.e. above and beyond the memory 
> required to run the system) to get a half hour buffer.  Besides saving a 
> little wear on a HDD, the RAM buffer wouldn't provide any benefits (bandwidth 
> is not a limitation for video playback).

You're saying that a half hour buffer is small?????  I'm having a hard
time imagining any situation where I'd want to rewind live tv that I
was watching by more than 30 seconds or so.  I mean, how long does it
take to grab a remote after you say "what did he say?" or "was that a
wardrobe malfunction?"   Ideally, I'd say that you'd get maybe a
minute or two in RAM, and then if you hit pause or rewind or something
then you'd hit the disk for a larger buffer.  But anyway, that's just
something else for me to play with, I suppose...

>> Anyway, maybe some of those questions are confused, but it's mainly
>> because I have a very poor mental image of the mythtv architecture,
>> and can't find any documentation that explains this.  Does anyone know
>> of something decent that's out there for me to read?
> IMHO, the best way to learn is to set up your system.  I doubt that anyone on 
> the list set up their dream system on the first try, but that's what makes 
> Myth so great--there's always room to improve your configuration and since 
> it's "free" ( http://www.fsf.org/ ), you're free to modify it as much as you 
> like.  And, the funny thing about the "dream" Myth system is that it's a 
> moving target.  The closer you get to your dream system, the more you learn 
> about Myth.  The more you learn about Myth, the more ways you can imagine to 
> improve your configuration.  The more ways you can imagine to imrpove the 
> configuration, the farther you get from your dream system...  :)
> I set up one Myth box as a test system and used what I learned when setting 
> it up to make a second system even better.  My main production box has gone 
> through many different changes throughout it's lifetime--from all local hard 
> drives to network filesystem to all local hard drives and that's just one 
> example.  If you approach a Myth box as a way to learn, it's well worth the 
> amount of time it takes.  If you just want a digital video recorder up and 
> running really quickly so you can record every episode of Lost and you don't 
> particularly want to spend time playing with it, you might be better off with 
> a TiVo.

Yep, I've decided I just need to "take the plunge" and start mucking
around with it.  The funny thing about all this is that I really don't
watch TV, so would never consider buying a TiVo -- I'm interested in
this just because the technology looks very cool to play around with.
I just wanted a clear picture so that I didn't spend lots of money and
then later decide "Oh, I really don't want to do it like that..."


Steve Tate
srt at cs.unt.edu

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