Hi,
I have been experiementing a bit and was wondering....

Sometimes its useful to have a second X window client running for various reasons. So that is easy enough to start

drop to the command line and type

startx -- :1

use ctl-alt-f7 to get to first frontend and clt-alt-f8 to get to the second frontend.

The command will kick off a second MythTV frontend in a default knoppmyth install. Seems to work just fine as long as you don't start a TV show on the second frontend and switch to the first frontend and start a show there as well. That locks your PC...

But you can start a show on your first frontend and switch to the second frontend to manage recordings, check status, etc. Its kind of neat. Also you can exit out of MythTV Frontend and start an xterm for system maintenance.

However, since MythTV is designed to work with multiple frontends, is there anything inherently dangerous with a single backend and multiple frontends running on a single computer?

Just wondering...

Thanks!

Andrew Lynch

No, there is nothing inherintly dangerous about running multiple front ends against a singe back end. That was part of the design of MythTV to begin with.

The only thing to watch out for with two front ends on the same system is what you have already discovered, trying to watch two shows at the same time. I think the issue is that the internal player expects to have more or less direct access to the hardware, and when you send two video streams to the hardware at the same time, X is having problems figuring out what to do with it. As a result I suspect it is X that is locking up. (A way to check this would be to see if you can ssh to the box from another system. If you can then it is X that has failed, not the system. If you can't then you probably do have a hard failure.)

You can also install gdmflexiserver which you can launch from an xterm, and that will allow you to run multiple X sessions as well. At least I am able to do that on my Mandrake boxes. I have not tried it under KnoppMyth. This gives you a system in X similar to what you can do on Macintoshes with OS-X these days.

About the only hazard with locking things up is that since you are not doing a proper shutdown to reload your system, the partitions are going to be in an unclean state. This will cause your system to either force a fsck, or even drop to a password prompt requesting that you perform an interactive fsck on some partitions. In most cases recovery is fairly quick, though there are exceptions, and you don't get a lot of useful instructions as part of the process.

-Rusty

_________________
Master:
- AMD 1800XP on a MSI KT4V motherboard, via KT400 bios
- 120 G Segate Baracuda /, /cache, /myth, swap
- 200 G Segate Baracuda /myth/tv
- 3 Haupauge! WinTV PVR250s
- 19" Daewoo Monitor (1280x1024 ni)

What if you were using multiple (supported) video cards or a combination of PVR-350 outputs and video cards, each with X running a separate server on each? Would that make it safer?

(This is aside from the speed problems of PCI vs. AGP and/or a vendor's video card/chipset drivers that can't handle multiple cards well. Worst case scenario is it works, but isn't useful due to performance problems.)

I guess the more to the point question is: does the mythfrontend software make any assumptions that would contraindicate running multiple sessions on the same machine (assuming they were all run from separate X sessions using separate video hardware output)?

-brendan

While it may work (log in as a different user and use a different id), I would not recommend this.

_________________
cesman

When the source is open, the possibilities are endless!

Thanks. If you have the time, could you explain your main areas of concern? e.g. potential problems intrinsic to mythfrontend (and related code) or, alternately the difficulty of the X/video_drivers/etc. issues?

-brendan

I don't think it is a hardware problem in the case you are describing, (two different video cards, two seprate X sessions :0 and :1) for video. I am not as comfortable with how well it would work for audio, though I am sure it could be done. You may even be able to use Jacks, or some other audio mixer to accept multiple audio sources and mix to a single audio out, though listening would very likely be somewhat confusing.

I agree that one way to do this would be to have each front end running as a different user. Doing that would require that either each X display log in as a different user automatically, or the first display would log in automatically, and you would need to manually log in the second display.

I am not sure how well lirc would work. You would probably have to dedicate a key to switching displays via a macro of some sort. There is an unlabled key on the Haupauge!, which currently does have an assignment in the lirc file in the /home/mythtv/.mythtv/ folder. You would want to see if that key makes sense to you. I would recomend adding some way to indicate which screen has the remote or keyboard, as I don't think it would be intuitive without having osd's come up, all too often finding that the screen you thought was active isn't.

As an alternative, you could use something like Linux Terminal Server to attempt what you are proposing, and see if you can get a good output to external terminals. I don't think this is a great idea, in that you will be attempting to drive live video and audio across ethernet, but for a single session this might work out. Setting up and using LTS is not something I have done. So I can't offer you any specific advice. There are tutorials out there though.

In all honesty you can pick up a small case, reasonably fast processor and motherboard with an nForce biose, ethernet and audio, as well as an onboard nVidea video card with s-video out, and build up a seprate front end for a lot less than the amount of work you are talking about putting into trying to do two front ends on a single box. If you wish to persue the idea of a single box dual front end, you are going to be doing a lot of exploring into untested stuff as far as KnoppMyth is concerned. I have not delved deep enough into the inner workings of the MythTV software to tell you where any of the potential pitfalls I have not already describbed may be.

At the same time, I am sure that there are more than a few people out there who would love to be able to have a multi-head front end where they can be monitoring the weather channel on one tuner and monitor, and a news channel on another tuner and monitor. Possibly streaming off one video card with dual tuners. (Which the last I checked was not working yet in a stable manner, it may be working for all I know)

If you do decide to strike out on your own, I think I speak for a lot of people that we would appreciate it if you would document what you find does, and does not, work, posting that here and on the wiki.

~Rusty

_________________
Master:
- AMD 1800XP on a MSI KT4V motherboard, via KT400 bios
- 120 G Segate Baracuda /, /cache, /myth, swap
- 200 G Segate Baracuda /myth/tv
- 3 Haupauge! WinTV PVR250s
- 19" Daewoo Monitor (1280x1024 ni)