Hi, I have installed KnoppMyth to the following system:

PII 350MHz
SE440BX motherboard
384MB SDRAM (3x128MB @ 100MHz)
160GB Hard Disk (Western Digital WD160BB)
GeForce 4400Ti 8x AGP (overkill)
Medion tv-tuner (based on saa7413 from philips, got it to work)
A PAL TV that is connected via a S-Video to composite connector to the TV.

I've got it to display on my PAL TV (I set the resolution to 720x576 in XF86Config-4 and used COMPOSITE) but when I watch live TV, it is slow and jerky. I haven't even dared to try and record something because that would probably mean a non-responding computer.
Because I have a good gfx-card in there, I wanted to know if it is possible to put more stress on the GPU and less on the CPU. Some general speed optimizations are also much aprriciated. (Also when recording/watching recording: a codec that uses the GPU's hardware encoding instead of CPU)
Because I'm displaying on a TV, I don't need the incoming signal to be adjusted (I don't need it to be de-interlaced because a TV is interlaced, I don't need it to be stretched out (same amount of pixels), ... etc). I just want the raw image from the tuner to the tv-out with the least of stress on my CPU.

I also like to know how you permanently change the keyboard layout to azerty. In a console mode (ctrl-alt-f1) when I use "loadkeys azerty" I get a working azertt-keyboard like I want it. I've allready changed in in XF86Config-4 but that doesn't seem to change annything (both the console and mythtv (ctrl+alt+f7) stay in qwerty).

I also like to get my USB-stick working, more on that here: http://mysettopbox.tv/phpBB2/viewtopic.php?p=64156

And (I'll stop after this one, guys ) I had to connecte the sound from my TV-tuner card to the sound-in on my motherboard that is normally used to connect to a CD-ROM drive (I hope you guys understand this) because the (old) mobo doesn't have a sound-connection for TV-tuner cards. I haven't been able to get my sound to work, is there some way where I can configure the source of my sound (which should be something like "CD-player")


Thanks

The Crazy Noob - A linux newbie

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Hi. A machine of that spec is barely capable of being used with MythTV, especially with analogue TV (unless you had a hardware accelerated capture card).

You can get better performance by turning down the capture resolution, (I think it is in Settings -> TV Settings -> Recording Profiles), but that just means a blurrier picture.

I have had reasonable success with an analogue card on a PIII 800, or digital cards on a PIII 500, but I don't think a PII 350 will cut it.

Of course, you could use this machine in a split setup (separate frontend and backend), but digitising/compressing and decompressing analogue TV is CPU intensive. You would be better off with either digital TV cards,a hardware-accelerated capture card (e.g. PVR-250), or a much faster CPU.

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Hi,

I have had some experience getting low-end systems to work with MythTV. You should be able to get some level of performance out of your system. I have gotten a P2-266MHz to work at some level as a PVR.

I think the previous poster is correct though, I recommend reducing your horizontal capture resolution by 50% or more. It is the video playback process which requires most of the CPU throughput so if you reduce your load it will improve playback quality dramatically. You will probably be surprised at how little this affects video quality. Keep the vertical resolution at 576 if possible.

Try 352x576 resolution and see how that works out. Failing that, fall back to 352x288. A P2-350MHz with a NVidia card should be able to do that much.

Make sure you are running the proprietary NVidia driver and not the NV driver. Avoid deinterlacing until you get the playback to work correctly first.

You may want to experiment by getting the record function to work, then the playback. Trying both simultaneously is extremely demanding so try them separate until you get them to work properly. Avoid watching "live TV" until the record and playback functions are working separately as it is the worst case system load.

Also, reduce your screen resolution as much as practical to say, 640x480 or 800x600 at most. 720x576 would be ideal if possible. Larger resolutions are CPU intensive and require expensive scaling.

Make sure DMA is enabled for your harddrive. Do a search on the forum and you will see there is a package called "hdparm" that will set your HD to perform at maximum efficiency.

You may want to look into getting more memory as well as that has a large effect on slow system stability.

You can get your sound card to work with alsaconf and alsamixer programs. I recommend using the external patch cable from the TV capture card to the "line in" on the audio card or motherboard. I would avoid using the internal lines until you get that working.

Getting the USB memory stick to work should be no problem. Just do:

mount -t vfat /dev/sda1 /cdrom

substitute vfat for whatever filesystem you are using and /cdrom for your mount directory.

Best of luck.

Andrew Lynch

Thanks for the reply, I'll thry the things you have propose and I will post the results (or problems)

By the way: the screen resolution allready is set to 720x576.

Howerver: about reducing capture resolution: I allready get jerky video when I'm only watching live TV, no recording or playback going on there. Maybe if i change the resolution of linux to 360x576 (50% of horizontal resolution) but I think that it will look very disorted.

I still want to know if it is possible for most of the work to be done by the GPU instead of the CPU because the Gf4400Ti is definately powerfull enough to do those things (at normal PAL resolution).
You said that video en/decoding requires most of the CPU time, can't this be done by the GPU? I tought that there were some codecs that would allow that...

[edit]
Ok, the recordingprofile settings have fixed the choppy playback. I had the software encoder for livetv set to 720x576 at first but that was obviously too much. But which one is the better: the RTJpeg or the MPEG-4 mode (I tought that the last one could get some hardware accelleration?). Should I use MP3 or uncompressed audio for the livetv-profile? (I don't see why it should get encoded and then decoded again??) Is the liveTV-profile only used when watching tv or is it also used when recording (then it would make sense to encode the audio to mp3)

[edit2]
DMA is enabled on my harddrive (I did: "hdparm /dev/hda" and it showed "using_dma = 1 (on)" )

[edit3]

Where can I check this?

[edit4]
Alsaconf doesn't recognise my sound card. It's a "Creative Soundblaster AWE 64" (Model number CT4380, in an ISA slot)

When I do "modprobe snd-sbawe" however, it seems to load up fine and i can use alsamixer. I still haven't managed to get sound yet and when I reboot, I have to do the modprobe-command again. Is there some sorth of startup script where I can put that command so it loads up every time (that way, I can allso make shure that "loadkeys azerty" is executed at boot)

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good


false - if you are using MythTV to watch live TV you are recording video and watching it from that recorded file. The live TV is cached into file and read from there to implement the PVR functions (play, freeze, rewind, etc).

Watching live TV is the most stressful thing you can do with a MythTV PVR, especially with the HD modes. Try breaking your testing up in to getting recording and then playback modes to work.

Don't worry about square pixels or wierd sounding capture resolutions, the horizontal and vertical resolutions are scaled into a PAL 5x4 display ratio regardless of capture resolution. That way even strange capture rates like 352x576 come out looking "normal" on your TV display.



Using the proprietary NVidia driver will do this to the extent it is possible. You can use XvMC IFF your TV tuner card records in MPEG2 format. NVidia GPUs will only help with the video playback and some decoding of MPEG2. Encoding is done either entirely on the CPU or on hardware accelerated TV tuner, not the GPU (to my knowledge).

Most frame grabbers record in raw bitstream or RTJPEG so XvMC is not useful. Only hardware accelerated tuners or DTV tuners (PVR-250, etc) record directly to MPEG2



definitely RTJPEG is a lighter load on the CPU. You can reduce compression quality to further reduce CPU load as well.

Realtime MPEG4 encoding is very stressful and CPU intensive.



uncompressed is less CPU load but uses a lot more space.



That is the way PVRs work... Live TV is really *almost* live recordings of TV you are playing back. Watching live TV forces the PVR to do all its basic functions simultaneously which can be quite stressful on the CPU. Especially if you are using a frame grabber (no HW acceleration) tuner.

Its the video playback that really hammers the CPU. Recording is a lot less demanding.



there are a bunch more settings but DMA=1 is the important one. Once the other things are fixed, try tweaking 32 bit transfers, etc.



there is a script to install it in KnoppMyth. It is called install-nvidia or something like that. At the command prompt, just type in "install" and press tab to see which command it is



Yes, there is a way -- several actually. I just make an init script job to run on startup. KnoppMyth is basically a modified Debian so do a search on update-rc.d and it will tell you a method. There probably is an official KnoppMyth method I am not aware of as well.

I would just install them manually until you find out whether your machine is suitable as a PVR or not.

http://www.debian-administration.org/articles/28

Thanks!

Andrew Lynch

In terms of update-rc.d, the KnoppMyth method is the Debian method. No difference.

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I've just set the resolution form 720x576 to 640x480 because the text in ctrl-alt-F7 was unreadable (after exitting mythtv). Howerver, after changing the resolution it appears as though the size is still the same (resolution didn't change). Is there a way to show the current resolution of the screen to make shure that it changed? In windows, you can change the DPI of your screen so you get bigger text, is that possible in linux too?

Also, in the text-modes (ctrl-alt-F1) the text is bigger but still not perfectly readable. I've find something on the internet about settting "font 8x8" in the modeline but that doesn't work. Is there a way to increase the font size?

I got liveTV working smoothly (@ 320x480) so recording and playback sepperatly must work too. Still problems with the sound though.

Scince it appears that the GPU won't help that much: I've got another similar system laying around here with the same processor but with an onboard gfx and soundcard (nvidia riva 128 and some soundblaster I think). It only has 256MB of RAM. Would the preformance on this system be comparable to the one I'm trying to get working now?


Sooo many questions

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You'll have to make the changes in the /etc/X11/xorg.conf file. Try

dpkg-reconfigure xserver-xfree

or

dpkg-reconfigure xserver-xorg

depending on which X11 you are using. I think KnoppMyth uses xfree86 but they may have upgraded recently.

You may want to just edit the /etc/X11/xorg.conf (or /etc/X11/XF86Config-4) file directly so that you can explore even lower resolution modes such as 512x384, 400x300, 320x240, etc depending on what your video card supports. You'll have to experiment to find those extra low res modes though...




There is info on this in the forums but I do not recall the specific instructions. You'll have to do a search.



cool! progress!

Thats true, if you can watch live TV decently, everything else pretty much works.


try:

echo "snd-sbawe" >> /etc/modules

reboot and see if that doesn't fix your sound issues.



be careful, the NVidia Riva 128 is *NOT* supported by the NVidia proprietary driver so you will not get its benefits if you try to use it. The FOSS NV driver does support Riva 128 and will give you Xv but still it is very slow. It is not really suitable for video unless its on a fast CPU system. (I had a Riva 128 and gave it away for exactly that reason)

If I recall correctly, only the NVidia TNT and later are supported by the proprietary driver and it is pretty much essential to making the older PCs to work properly in my opinion. Take it for what its worth.

If your current system has more RAM and a supported NVidia card using the proprietary driver, then it will beat the pants off your other system running MythTV.

GPU offloading only really works (that I know of) with MPEG2 video format. That is why the PVR-250 (and similar) with a NVidia video card with XvMC is such an awesome combination on low-end PCs.



sooo many blank stares. Good thing they are still free

Thanks

Andrew Lynch

I haven't yet tried to change the linux resolution, but when I change the livetv encoder resolution, in particular the vertical resolution, to annything else but 576, I get a lot of interlacing going on and the picture looks bad when the camera moves around.
My currend modeline (generated by some prog on the net) is: (in file: /etc/X11/XF86Config-4)


Maybe if I change both the linux-resolution and the capture resolution (like both to 512x384 as you suggested), I will ged rid of the interlaced-look.
(In the playback option of mythtv, I have deselected "deinterlace" because a tv-screen is interlaced itself, but this is for the recorded interlaced image I guess, so maybe I should turn this option on? But then agian I will put extra stress on the CPU)

The solution for the sound that you posted doesn't work. I am however conviced that my soundcard now works (I can get into alsamixer) but I think the problem lies in the input. As I said before, I have connected the sound-out form my tuner card to the cd-sound-input from the sound card with a cable I had laying around. I think mythtv is searching in the wrong input. How can I mannualy select the CD-in channel as the channel to get the tv sound?

When I get the sound-problems fixed, the only minor thing is that I would like to delete some channels (so that mythtv doesn't display them, scince I don't use them annyway) and I need to adjust the name etc for them properly and their number (I mean to change the sequence). I've allready found this about the issue: http://www.mythtv.org/wiki/index.php/XM ... nnel_Setup but for some reason I can't seam to access mythweb (I used the lynx (text based) browser built in in knoppmyth and tried to connect to http://127.0.0.1/mythweb on the linux box but it wouldn't let me connect and I don't realy feel like doing the other way mentioned because it would take a loooooong time).

Annyway, I'm slowly getting there and I just can't thank you enough for the information you have already given me! *bows and kisses feet*


[edit] I tried to write a script (my first in linux ) to speed up the proccess of changing the channel name and frequency etc.

But everythime a "mysql ....." line gets done, I don't get any output on the screen (just a blank line).

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Well, video signals like NTSC or PAL are not based on square pixels or a digital signals. As you discovered, when dealing with capture resolutions even slight changes the vertical resolution has drastic effects on playback quality while wild swings to horizontal resolution has surprisingly little effect on playback quality.

I recommend keeping the vertical at 576 and shrink the horizontal resolution as much as you need to get decent live TV performance. You may end up with some very strange sounding capture resolutions like 240x576 but I think you'll see it will still look passable especially compared to 720x288.



maybe, but you'll likely fall into another trap that will cause problems

The purpose of the lower resolutions is to match the vertical capture resolution with the display resolution for the best playback quality with the minimum CPU loading (ie, eliminate the video scaling operations)



if your vertical capture resolution does not match the vertical display resolution, you will have to use deinterlace to minimize interlacing artifacts and get decent playback quality. However, then you fall into the dual trap of requiring CPU expensive video scaling AND deinterlace operations which are going to crush your low end system CPU.

Now if you have a P4 3GHz or Athlon 64 X2 or better with a NVidia card w/proprietary driver, you can have deinterlace and scaling all you want you'll never notice it because the extra load from those operations are practically free with that much CPU horsepower. However, with a low end CPU those operations are a killer.




if your problem is the alsamixer, then follow this procedure:

Run the ALSA mixer control. Press F5 to see all the controls, playback AND capture.

$alsamixer

set:

Master to about 70

PCM to about 70

Line to 0, capture, and MUTED

Capture to about 70 and CAPTURE

Set everything else to 0 level and/or MUTED you can





you can edit channel listing easily in the mythtv-setup program

I'd use that before wrestling with mythweb. It works but requires some tweaking to work properly.

Best of luck.

Andrew Lynch

I have changed monitor settings: the refreshrate to 100Hz, not interlaced and the resolution stayed at 720x576. The higher refresh rate helped to get a clearer image and to reduce the interlace-lines on screen.

I've tried your settings for the sound but I still can't get it to work. I've allso tried to change the settings for "CD" but to no avail. (at CD it said: playback, not capture maybe there's something wrong there ...??).
If there isn't any other solution I'll try to find a cable that goes from the 4-pin connector to a normal stereo jack connector to connect the tuner to th e line-in. I would however like to get the sound via cd-in method working because it's cleaner (everything is in the case, no external connector) and I don't want to spend much money (any money) on the project (scince it's very low-end to begin with)

I still haven't tried to change the cannels yet, but I will try so as soon as possible (so much to do, so little time)

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to adjust the sound settings with alsamixer, just start MythTV and press Alt-X to open an x-term. Then start alsamixer. You can change the capture device to whatever is connected to the sound card. You will have to press space bar to set the capture device. It should be line-in.

I recommend experimenting with the external cable and get that working first (as you know exactly what is connected to what) and then move up to the internal cabling method once you know your card is working properly.

Best of luck

Andrew Lynch

I've tried and I've tried to get the sound working but it still stays quiet. I've measured the output of the tv-tuner card with a multimeter and I could hardly see any signal (maybe a few mV). I think that there's something wrong with the output of the tuner card.
When I watch TV I get constant noise but when I change channels the noise drops out during the cange and comes back with the new channel.

I've searched the web and found this link (pdf-file for the 7134-chip)
Below is a quote from it about the sound, especially see the output section:


It appears as though the sound from the tuner card can also be streamed via the PCI port. Maybe I can get sound to work that way. And maybe the output-connector isn't active (at least I don't think it is) because you need to configure the sound to go to that connector/the PCI port.

In that pdf, there's also something about the TV-proccesing and it says something about hardware decoding and encoding (at least that's how I understand it)



Could this mean that I would be able to get some form of hardware de/encoding done by the tuner card?

(more info here: http://www.semiconductors.philips.com/pip/saa7134hl)



As said before this is my first experience with linux and the problems have kept coming at me for days and days; one problem solved and two new problems show up. I am realy glad that you gus (in particular lynchaj) are so patient with me.

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Try plugging a standard headphones into the TV card audio jack. You should here the TV audio when you watch live TV. However, the audio will lag the video picture by a few seconds. That way you know your tuner card audio is working properly or not.

Are you sure your SBAWE sound card is working properly? Try testing it with

aplay [random file, preferably audio]

or

cat [random file] >/dev/dsp

you should hear noise come out of the speakers attached to the sound card if it is working properly.

When you ran mythtv-setup and setup your capture card, you picked a V4L card using /dev/dsp for audio, right?



As for streaming the audio directly from the card over the PCI bus... if you can get that to work it is definitely the better way to go.

You might want to search on your card to see what modules it requires.

Maybe try

modprobe saa7134-alsa

Is alsaconf detecting your TV tuner audio card? Are you seeing any level activity when you run alsamixer?

You may try this at the command prompt

dmesg | grep "saa7134"

and see what it says.

Best of luck!

Andrew Lynch

Alsaconfig doesn't detect annything (neither the sbawe or the saa7134). HOWEVER: if I do "modprobe saa7134-alsa" and then I check alsamixer, I can see three channels, all capture I think labeled: Line 1, Line 2, Video. I've tried changing their volume and selecting them as capture with the space bar but I still can't manage to get it working. Maybe it's because the worng number is chosen in mythtv (I mean dsp, dsp0, dsp1, dsp2 etc).

I have managed to find out that the sb-awe (soundcard) is seen as card 0 by alsamixer (if I do "alsamixer -c0" I see all the channels of the soundcard). The tuner (saa7134-alsa) is seen as card 1 ("alsamiwer -c1" gives the three channels of the tuner card "line 1, line 2, video).

Now that I know these things, how should I setup mythtv?
I've tried:

in mythtv-setup under capture cards: sound dsp
under mythtv settings in sound-out: dsp0

and:

in mythtv-setup under capture cards: sound dsp0
under mythtv settings in sound-out: dsp1

and some other combinations, but none have worked so far...

I don't think I have a working dsp1, only dsp and dsp0 because if I tried to do "cat [random file] >/dev/dsp1" I got an error about that device not existing.
doing cat [random file] >/dev/dsp and dsp0 gave me sound so that leads me to believe that dsp and dsp0 are both the soundcard (sbawe)
... but then which one is the tuner ... ??? [confused]

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