Knoppmyth R5A22.
This is kind of two related questions.... I hope I can make myself clear....

I've been reasonably happy with my myth setup. Last week, I finally got mythburn to work (just some directory permissions problems) and burnt a DVD of a DVB broadcast. Worked perfectly. Excellent picture quality.

BUT

(using an external DVD player) Watching the DVD of the broadcast, it has much better picture quality than what I see when playing the same program within myth. The differences I see are:

#1) The DVD has better color fidelity. Things played back in myth are oversaturated.... e.g. people end up redder than they should be. Either myth is mucking with the color response, or the nVidia card needs some tuning. But more importantly...

#2) The apparent frame rate on the DVD is higher than played in myth. I wouldn't say it is double, but to my eye it is noticeably faster. On the DVD motion is crisp and snappy, on myth it's a bit slower and blurrier (In my profession I work in CGI all day so i guess my eye is tuned to these things).

For the time being I'm ignoring #1 (but hints there also welcomed). It's #2 i'm more interested in.

I've never messed much with the X configuration other than what was autodetected so thats where i headed...

The setup: I'm running a nVidiaFX5200 via DVI to a Samsung 16:9 plasma screen. I hadn't changed anything from the default knoppmyth setup other than add a DisplaySize setting because of the 'small fonts' issue.

When I went and investigated XF86Config-4, the modeline entries state that they were intially auto-probed from the screen. I selected one that according to the screen documentation conforms to what is best for the screen (800x600, 60hz vert, etc). This improved how fonts look in an xterm, but no noticeable change in myth output quality.

My questions are:

a) Do I need to go through the procedure for determining a new modeline that a lot of people seem to do when I have these 'autoprobed' ones? Should they be good enough? I've gone through the XFree log output and looks like the video mode is being set up properly.

b) Anything else that could be interfering with the framerate output? It's not de-interlacing. I've tried all the possible combinations there. Flipping the TV between playing in myth, and playing the same program off a burned DVD is very obvious. Kind of shocking that a the output from a $45 DVD player is so superior.

Any hints welcomed!

thx! J

What makes you so sure that the problem is not de-interlacing?

One thing to remember is that most (all standard def?) DVB broadcasts are interlaced. In PAL land, they are 576i, 25 Hz and in NTSC land they are 480i 30 Hz.

The next thing to remember is that plasma display technology is inherently progressive. This means that when you display interlaced content on a plasma screen, it needs to deinterlace it. This would normally be done by the plasma screen and the quality of its deinterlacing is (or at least should be) one of the selling points of plasma screens.

Another thing to remember is that some DVD players are capable of displaying progressive output instead of de-interlaced. In this case it is the quality of the DVD player's deinterlacer that is important.

Another thing to remember is that other than using a PVR 350, there is currently no way using mythtv and a video card to correctly display interlaced content. The bob deinterlacer probably goes the closest, but 50% of the time the odd and even fields will get displayed on the wrong lines making the picture appear to bob up and down if you look closely.

The last thing to remember is that hardware deinterlacers (as you would have in the plasma screen and also in a progressive scan DVD player) would usually do a better job than a software deinterlacer.

So your myth box cannot deinterlace as well as the plasma screen, and it is unable to reliably provide a properly interlaced signal to the plasma screen to let it deinterlace it, so you get screwed both ways.

One glimmer of hope was this thread, but that seems to have died out: http://www.gossamer-threads.com/lists/e ... ply;so=ASC

>>What makes you so sure that the problem is not de-interlacing?

Not 100% sure there but my comment was based on changing the settings within myth made no appreciable difference.

>>So your myth box cannot deinterlace as well as the plasma screen, and it
>>is unable to reliably provide a properly interlaced signal to the plasma
>> screen to let it deinterlace it, so you get screwed both ways.

Crap. Makes sense. So what does myth do? e.g. You've got a DVB signal coming in at 50 fields/sec. Is it only putting out an image at 25 frames/sec always? (with quality variations depending on the de-interlace settings). That would totally explain what i'm seeing. The output quality looks like stuff that is shot on film -- slower blurrier motion, instead of quick and snappy like video.

Shame this isn't something that myth handles well considering all the progressive scan sets coming up now.

I'll have to give BOB de-interlacing a try again with my new modelines. When i tried previously, the OSD was a flickering mess.

I think that Bob is the only deinterlacer that doubles the frame rate (i.e from 25 to 50 for PAL or 30 to 60 for NTSC). This, in my opinion is a completely braindead. Any deinterlacer worth it's salt should be producing a full frame for each field rather than for each frame, otherwise it is destroying one of the strengths of interlaced formats. Anyone with a mildly discerning eye will see the sort of slow frame rate problems you can see. I'm amazed that this is the current state of mythtv. I hope the situation improves. I guess eventually everything will be high def progressive? But it'll be a long wait.

I gave BOB a try again, and at least with mysetup (which isn't anything sophisticated) the OSD still flickers unacceptably.

Oh well. Back to kernel.

I have an older nvidia card (geforce2, so I use nvtv to set overscan, colour saturation, contrast etc). It also has a flicker control. This blends horizontal lines of pixels before sending them out the TV out, and in doing so reduces flicker. I turn it completely off, because I believe it gives a better video quality, but it does make the menus/osd flicker a bit.

Your newer card should have similar controls via nvidia-settings. I would switch back to the Bob deinterlacer and then use nvidia settings to see if you can adjust the flicker controls such that the osd flicker no longer annoys you. I use the blue theme (just because it is the default) with the default osd theme. Other themes may be worse for flicker. It depends on whether they have sharp horizontal colour/brightness contrast.

You read my mind Greg -- my next question was going to be how to tune the color response on the card. I'm getting tired of people having skin tones that range from almost normal to rather sunburned. The saturation needs some calibration.

does nvidia-settings work for the DVI/VGA output or just the TV out? (I'm using DVI).

Cheers and thanks again!
j