Mythtv HDTV-related work/patches

The Chromakeyed OSD

This changes the Xv and XvMC display methods from using a blended YUV overlay to using the chromakey window behind the video. This removes the OSD processing from the timing-critical code where you're trying to stay on a strict schedule for frame rendering, and I have found it tremendously helped eliminate delays in frame rendering which I believe cause the "prebuffering pause" problem when the OSD is displaying.

It also prevents us from having to render and alpha-blend the OSD for every single frame. Because the chromakey window is persistant, the OSD rendering only needs to do hard work when the OSD changes. This also means that, if the video is not filling the screen (i.e. letterbox-ing or pillar-ing), we can (and do) still use the full screen for the OSD.

Lastly, you get full color for the OSD of course. :-)

The results are surprisingly good. I initially did some experimentation with putting text and images on the chromakey background window, and was sufficiently encouraged by the results to go ahead and do this full-fledged proof of concept implementation.

Drawbacks

You give up translucency in the OSD. You still have the equivalent of transparency courtesy of chromakey.
The OSD is still rendered as YUV, and this code converts it to RGB. It would be much better if it were simply rendered as RGB, but a) this is a proof of concept and b) I haven't figured out how to do that yet. :-)
Some may consider it a drawback that this spawns an additional thread just to manage the OSD. I did it that way so that the OSD display activity is partitioned away from the video and audio playing activity. This allows the OSD activity to be run at a very low priority, and it allows adjustment of the rate at which the OSD is (re-)evaluated. At present it's set to check the OSD every 33333 usecs, which roughly corresponds to 30 fps. It could just as easily be a higher (slower) value, though, to reduce CPU usage by this thread at a cost of a slightly less responsive OSD.
The OSD fonts are anti-aliased, which can make the edges look strange under some circumstances since the anti-aliasing doesn't understand that black is actually "transparent". I tried to combat this by using half-toned outline colors, but it's not entirely successful.
Since I haven't actually disabled the YUV rendering code for the OSD, you can get some strange results with certain colors (red?) as the OSD code thinks it should alpha-modify your colors.

Like I said, it's a proof of concept - not a glossy finished product. This is intended to stimulate discussion, and to find out if others benefit as much as I have from moving the OSD processing out of the frame rendering loop.

There is the patch itself (last updated 4/20/05) and an example OSD theme (last updated 3/23/05) that, despite my complete lack of artistic skilz, attempts to show what the chromakey OSD can do. Let's just call it (ahem) minimally artistic. :-)

I have been using both patches for several weeks now on my nforce2 system with built-in graphics (which has to be some sort of worst case since it's using main memory), and have found that I can now view 1080i content with near perfect results. I still encounter the "jumpies" and "old-framies" with 720p content, but I think that's a different problem.

Notes:

The patches are against cvs as of 3/22/05
You'll need to define "CHROMAKEY_OSD" when building in order to enable it.
Just for now, you need to set the XV chromakey color to black explicitly before starting mythfrontend because my code to set the chromakey color doesn't seem to work. If someone can tell me why my code to set the color isn't working, I'd be grateful. I use this in my .xinitrc:
```
	xvattr -a XV_COLORKEY -v 0
```
I only watch video in fullscreen mode as this is a mythtv-only box in the den. I really don't know if this will work when using less than fullscreen mode. I suspect I've missed some sizing subtleties...