[mythtv-users] System specifications review...

Johnny jarpublic at gmail.com
Mon Nov 16 19:27:19 UTC 2009

>>I don't even know
>> if I could tell the difference between 1x or 2x deinterlacing
> 2x = double framerate.  The deinterlacer (as I understand it - open for
> correction) takes the (in my case - UK) 25fps and increases that to 50fps
> resulting in a much smoother picture for TV's capable of displaying it.
> Can't say I've seen them working in VDPAU, but the difference for me between
> linear blend and Yadif(2x) was immense.

There is more going on than just increasing the frame rate. See this
site for a good breakdown on deinterlacing and the pros/cons of
different methods (http://www.100fps.com/index.htm#howto). Interlaced
video has 2 fields (half vertical resolution) that are combined to
make a single frame. With PAL this would be 50 fields per second
combined to make 25 frames per second. However, just combining the
fields into a single frame gives you that classic saw tooth look
because a little bit of time occurred between when each field was
captured, so they don't line up where there is motion. Advanced 2x is
referred to as temporal-spacial deinterlacing by Nvidia. So it is
processing over different fields (temporal) and it is processing with
in the field (spacial) to identify where the motion is and then using
their algorithms to combine the fields to create sharp smooth images.
With the 1x deinterlacers you would create 25 frames from the orignial
50 fields, so you would lose some of the temporal information to gain
the complete vertical resolution. With the 2x deinterlacers they
create 50 frames from the 50 fields so you get full vertical
resolution and you get all of the temporal information as well. Doing
this correctly is complex and computational intensive.

With regards to your power question, on the one extreme you could save
a lot of power by not having a mythtv system, or having a smaller TV.
My point being that the real question you are interested in is not
just will a discrete VDPAU card cost me extra energy, but will the
benefits be worth the extra energy. I agree with Mike that you aren't
likely going to save power by doing the decoding/rendering in your
GPU. But VDPAU does do a really good job at deinterlacing (better than
most TVs and much better than any of the software deinterlacers) and
for most people the increased picture quality is worth it. It varies
for everybody depending on your TV set and type of recordings etc. But
for me the benefit was dramatic and I personally wouldn't go any other
way than with VDPAU. And at $30-$50 for a card I think it is worth the
initial investment to see what you think of the image quality. Worst
case you sell the card.

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