In my mythfrontend log I see a lot of errors like this:

2007-05-10 06:53:57.392 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.392 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.430 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.430 VideoOutputXv Error: Child B was already marked as available.
2007-05-10 06:53:57.431 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.431 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.431 VideoOutputXv Error: Child B was already marked as available.
2007-05-10 06:53:57.431 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.432 VideoOutputXv Error: Child B was already marked as available.
2007-05-10 06:53:57.511 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.512 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.512 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.512 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.513 VideoOutputXv Error: Child A was already marked as available.
2007-05-10 06:53:57.567 VideoOutputXv Error: Child C was already marked as available.
2007-05-10 06:53:57.567 VideoOutputXv Error: Child C was already marked as available.
2007-05-10 06:53:57.569 VideoOutputXv Error: Child C was already marked as available.
2007-05-10 06:53:57.570 VideoOutputXv Error: Child C was already marked as available.
2007-05-10 06:53:57.570 VideoOutputXv Error: Child C was already marked as available.
2007-05-10 06:53:57.570 VideoOutputXv Error: Child C was already marked as available.
2007-05-10 06:53:57.651 VideoOutputXv Error: Child C was already marked as available.

Can somebody point me where problem might be ?

HW: P5P800, C326, GF5200, R5E50
I have "color OSD" tweak enabled.

thx in advance

Doing some searches it looks like it may be related to your nvidia driver, have you updated that lately?

Also, it seems that most people seeing it are using HD format, is this true for you?

When does this error occur? When just watching recordings, or does it start when fast forwarding?

Talk about answering a question with questions!

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Well,
Yes, I upgraded to 9755 - no difference
But I reduce frequency of this errors by enabling "Vsync to OpenGL" in myth TV playback settings and "SyncToVBlank=1" in nvidia-settigs-rc.
Before there was quite a lot of those errors - mainly when FFW/REW but also when OSD pop-up/fade away. When they appearing - I have also drops in sound.
Now they are rare and and no audible drops in sound . So it looks like those settings are helping somewhat, but not totally eliminating a problem

bbear may be interested in the settings you are using and how they are affecting playback while the OSD is up: http://mysettopbox.tv/phpBB2/viewtopic.php?t=15141