[vdr] Advice on new motherboard, xineliboutput, vdpau, hdmi video & audio, etc.

Thomas Hilber vdr at toh.cx
Wed Aug 25 19:45:30 CEST 2010


On Wed, Aug 18, 2010 at 10:13:56AM +0200, jori.hamalainen at teliasonera.com wrote:
> Computer hardware usually cannot provide 50.000Hz, 59.940Hz or 23.976Hz
> outputs to your TV/Monitor. This will cause some judder on display output
> as MPEG/AVC input-stream is not synchronized to output framerate.

it's correct that computer hardware normally cannot provide 50.000Hz. Nor 
can it adapt the framerate dynamically as I did for some handpicked hardware
in my sync-fields-project [1].

But even in the case of non synchronized output framerate (VDPAU) it does not
necessarily mean that judder will result.

Nvidia graphics use excellent deinterlacers. These produce a stream of
progressive frames with field frequency (e.g. 50Hz) out of an 
interlaced source.

Single frame doubler/losses at 50Hz are not visible to the human eye. To
put that in other words: VDPAU uses some brute force (deinterlacing)
to work around their design flaw (missing synchronization). In practice
this works very well.

Surely it's not an optimal solution: the price for that is excess graphics
power requirement if you think in terms of 5W units. But nonetheless 
the smoothness of picture flow is excellent.

If some people report they observe judder though this mostly is a result
of a wrong setup (xorg.conf) or use of temporarily broken beta 
software (xine derivates). With VDPAU design there exists nothing like
inherent judder.

For the future I wish there once will become available some graphics with
native dynamic framerate support. Never seen such thing until today.

cheers
   Thomas

[1] http://lowbyte.de/vga-sync-fields/vga-sync-fields/



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