[mythtv-users] MythTV questions...

Eduardo mythtv at ease.mb.ca
Wed Apr 7 13:05:42 EDT 2004

John Sutherland said:
> Hi guys/gals..
> I just setup and got working a basic mythtv box, and I have some
> questions..
> First, a little about the system it its on.. I'm using this box more of a
> proof of concept for myself.. It is a Pentium II 400Mhz, 128M, PVR-350,
> and a "broken" 40G drive.. By "broken" I mean that I can not get more than
> 2M/sec rates from hdparm -t.. The drive works, its just slow... I'm using
> the 350's TV-Out, and for a distrib, Gentoo...
> Now for the questions...
> 1) I've noticed that channel changing is ---slow---.. Nearly 30 secs to
> change the channel... I'm assuming its either the slow drive, or the slow
> processor.. Which do you think it is?

There is always a delay as the backend buffers up some of the video (more
on that later). 30 seconds seems very long. Unless everything is playing
VERY SLOW, and this is just adding to the channel change time.

> 2) What is the difference between the frontend and the backend? I haven't
> seen a good description of what both of them really do... Does the backend
> do the storage?? If I move my backend to another (much faster) machine,
> would that solve the channel changing slowness??

Backend controls the tuners and records the shows. Even when you are
watching "live tv" you are really recording a show. If you didn't you
couldn't jump forwards and backwards. All the storage takes place on the
backend. The CPU power it needs is for doing the encoding.

The frontend accesses the backend to receive the video streams. So when
you change the channel on a frontend, it tells the tuners on the backend
to change. The CPU power it needs is for decoding the video data.

These rules all go out the window for all the other plugins, mythmusic,
mythvideo, etc, which all run on the frontend and don't have that nice
"client server" behaviour. This is why everyone seems to map drives from
the frontends to the backends. The backend usually has all the storage
capacity, so people put their images, videos and MP3's on the backend.

Note, the backend and frontend can be the same machine. You just need the
CPU power to do the encoding and decoding at the same time. Your 400 is
pobably slow, because it has to do encoding and decoding at the same time.

> 3) When using the TV-out on the 350, how's it really work? Does it read
> the input from the tuner, then store it to disk, then read it, and send it
> to the tv-out? (kinda related to the previous question I guess)

It is encoded by the hardware encoder on the PVR, stored to disk, and then
decoded through the hardware decoder on the PVR. The PVR takes away lots
of CPU load on both encoding and decoding.

> 4) Has anyone coded up a burner plugin? To burn DVD's, VCD's from recorded
> video? Or even music? If not, I might consider writing one..

Dunno on this one. Probably.

> Thanks guys/gals!
> --John
> --
> --John
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