[mythtv-users] bobdeint and asynchronous displays

Ian Macdonald ian at caliban.org
Sun Sep 24 09:30:21 UTC 2006


I recently moved away from my trusty PVR-350's TV Out to an XFX GeForce
FX 5200 video card for playback. It's connected to my Philips 37PF9830
LCD television over straight DVI (as opposed to VGA -> DVI), providing a
display that can go all the way to 1920x1080i. However, I'm actually
running it at the progressive 1280x720.

Getting XvMC to work was a breeze, the only hiccough being that my OSD
went black-and-white, but the fix is well-documented and was easy to

When using the TV Out of the PVR-350, I never noticed interlacing
artefacts. Perhaps they were there all along and the Hauppauge firmware
did a good job of deinterlacing; perhaps the display was interlaced at
that lower resolution; I'm not sure.

Now that I'm doing my MPEG-2 decoding in software, however, the problem
is readily apparent.

Because I'm using XvMC, the only deinterlacing algorithms available to
me are 'onefield' and 'bobdeint'. 'onefield' doesn't look all that
great, so I'll leave that out of this discussion.

'bobdeint' does a lovely job of cleaning up the picture, but, because my
display is not synchronous, I suffer from the phenomenon outlined in
section 10.4 of the MythTV HOWTO:

   "However, if the display is not synchronous, it will cause flickering
   or the appearance of the picture moving up and down by one line."

That's exactly what I have.

So, my ultimate question is: Do I have to live with either the
interlacing or the vibrating image? Are there no other options open to
someone with an LCD TV?

I suppose I could turn off XvMC and use kerneldeinit, but I'd rather
keep XvMC if at all possible.

I suppose I could also crank up my display to 1920x1080i, but that seems
crazy, because I have simple low-res PAL inputs. The only reason I run
1280x720 is because the Philips TV's EDID information is basically a
pack of lies, so this mode is the only one that is usable unless I
disable EDID and add my own modelines.

Anyway, I can't be the only one with a set-up like this, so what do
other people do to fix the problem of interlacing artefacts on an
asynchronous progressive display?

Thanks in advance,

Ian Macdonald               | Very few things happen at the right time,
ian at caliban.org             | and the rest do not happen at all.  The
http://www.caliban.org/     | conscientious historian will correct these 
                            | defects.   -- Herodotus 

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