It's taken me a while but I've finally managed to get my PVR system to a functional state. However, there are still some problems that I have not found a solution for.

1. Changing channels seems to be "Scientific Atlanta DVR" slow, in other words, painfully slow. It seems to take about 3 seconds to change a channel.
2. Starting to watch TV has, what I would consider, a huge delay before any actual image is displayed.
3. Trying to rip DVDs only ripped 3 tracks and only one of them was even close to the right length. There should have been 12 tracks. What gives?

Generally, throughout the front end there is a distict feeling of some input delay going on. Unfortuantely, this is exactly the sort of delay that is driving me away from the Scientific Atlanta DVR boxes. They are painfully slow. The Windows Media Center response was much faster.

Has anyone experienced these issues or am I just smoking crack?

System configuration:

Hauppauge PVR-250,
Duron 1.6ghz,
Elitegroup K7VTA3 motherboard (Fry's deal with cpu for $52)
512M ram,
230G WD 7200RPM drive
Geforce4 MX440 Video card with TV out

Using KnoppMyth R4 distribution with updated ivtv driver (works MUCH better than the original one with R4).

Couple of more points:

I'm using a Soundblaster Live! sound card,
Video does not seem to be getting synchronised to the start of the frame so there is ripping at various points during image display (looks like classic blitting without waiting for vblank).

How can I install a more comprehensive desktop in Knoppix? Any ideas? apt-get is present but I don't know which package to get. I'd like KDE.

knoppmyth isn't designed to provide a more comprehensive desktop.. It's designed to be as small as possible and still get the job done.
The 2-3 seconds to change channles isn't unreasonable at all. One thing you have to understand is that you aren't watching live tv. the computer takes the stream, encodes it how you have it set (In your case mpeg2 because you are probably using the onboard mpeg2 encoder built in to your pvr-250) and then plays it. The stuff you see is about 2 seconds behind live tv because of this. browsing tv channels the old fashioned way just isn't possible with a pvr setup. What I recommend you do is hit the option in the setup for tv that lets you channel change buttons just bring up the OSD and change channels on that. That's what I do and it works great. As for the tearing problems with live tv, it sounds like a symptom of buggy ivtv drivers.

2-3 seconds to change channel is absolutely unreasonable. This is the primary reason I no longer want to use the scientific atlanta dvr. Data comes from the capture card continuously and there is absolutely no reason to back buffer ANY data when changing a channel. I did not have this problem with Windows Media Center, and that's a Microsoft product!

I think that a channel change time of about 100ms is reasonable.

Now, for the frame sync issue, the ripping is caused by a couple of possibilities:

1. When rendering the screen image, myth does not do a wait for vsync.
2. The display is NOT double buffered.

This ripping of the display is also not present in MCE. It also happens when playing back video.

This is very important to me as I'm setting up the media system that will be in my living room for at least the next several years. I do not want it to be a step back from the Scientific Atlanta crappy software. I also absolutely do NOT want to use MCE. For some reason, I have an aversion to Microsoft products.

If someone can give me some pointers as to which part of the code to start looking at the channel change delays, and rendering delays, I can start working on debugging it myself.

MythTV is shaping up to be a fine product and I really would like to get in to the guts of it to see what I can help with.

Well sounds to me like you need to do one of two things.

1) take this up with the myth people. www.mythtv.org

2) go use MCE.

Does MCE have pause live tv functionality? that is what is slowing you down. yes the channels could change faster if you were just dumping the input stream to screen. but that's not what's happening. the input stream is getting encoded into a file then that file is being played back otherwise you wouldn't be able to pause. Granted this could probably be faster, particularly with a hardware encoding device like the pvr250, but myth also supports sofware encoding devices, and the delay is not unreasonable for them. probably the reason that MCE can do this faster if it has the pause functionality is because they require a hardware encoder so don't have to worry about accomidating all the other tv cards. plus I'm sure they had full documentation about the cards.

I think you should just use WMC. The thing about opensource projects is that they don't take well to people telling them what is absolutely not acceptable about their project. If you take this up with the mythtv people with the attitude you have shown here you will either be ignored or be flamed and you won't get any help.

"Data comes from the capture card continuously and there is absolutely no reason to back buffer ANY data when changing a channel"

That statement is completely untrue. The reason that the data is back buffered is so that you can get the fancy PVR funcitonality of pause, rewind, etc (I should also point out that it's not really backbuffering, the two seconds is the amount of time it takes to record then playback the stream. There's no part of the code saying that it has to wait two seconds, atleast to my knowledge). If you want to write some fancy code that plays the live stream from the card and then switches the user over seemlessly to the recorded buffer either after it is ready (This would be freaking hard to to unnoticed), or (here's an idea that might actually work) when they try to access the pvr functionality (ie. only switch them over if they try to rewind, pause, etc) then go ask the mythtv guys very nicely and they might help you. they can be reached in realtime on freenode on #mythtv.

Put it this way , I've written several movie players for the PlayStation 2 without any transition issues. Yes, the PS2 wasn't capturing video at the time but it was reading from multiple data streams off a dvd (and dvd's have MUCH higher latency than a hard drive). I don't see how on earth writing to a file and reading from the same file (as soon as the write is complete - which should be 1 frame of data, or every 29.97ms) should cause a 2 second delay. Thats 2000ms! A huge amount of time.

Now, like I say, I'm more and willing to put my work where my mouth is and assist in fixing this irritation. I see mythtv as the way to go for pvr functionality. Open Source software is the way to go. However, even if it is 'just' open source software, why on earth cannot we apply commercial levels of quality in the performance? Come on guys!

So, if you have any idea where I should start looking, I'd really appreciate it.

Well, 0.13 does cut down the wait time some! There has been plenty of discussion on this topic in the mailing list. I'm sure whatever code you can implement, fix or modify to improve this would be must appreciated.

_________________
cesman

When the source is open, the possibilities are endless!

Then join #mythtv and ask those guys nicely. cvs.mythtv.org is the webcvs of the mythtv project. knoppmyth is just a project to provide a simple machine install of mythtv.. We don't do any of the coding of mythtv.

Alright, I'm off to do that.

I had a couple of problems with the knoppmyth installation but those were fixed by updating ivtv, and fixing that xmltv channel fetch script.

Other than that, it went fairly smoothly.

Hopefully I can add some further input and work to make this a much more impressive open source project.

What IRC server?

irc.freenode.net

Can you describe where the option to do so is? I cannot seem to find it.

Thanks!

_________________
Retired KM user (R4 - R6.04); friend to LH users.

I don't have my mythtv box handy (I'm at my gf's watching over her because she had her wisdom teeth pulled yesterday morning) but I think it should be in tv settings. I think it's somethign like "have channel change change OSD" or something like that.

biscuit:

We would all be grateful if you could actually make this happen in a future version of MythTV, that's for sure. I was bummed when I found out... but as someone mentioned above, this is the only real workaround right now:


Settings -> TV -> General

Uncheck: "Change channels immediately without select"