--- On Tue, 18/1/11, Niko Mikkilä <n...@phnet.fi> wrote:

> From: Niko Mikkilä <n...@phnet.fi>
> Subject: Re: [vdr] Replacing aging VDR for DVB-S2
> To: "VDR Mailing List" <vdr@linuxtv.org>
> Date: Tuesday, 18 January, 2011, 13:06
> On 2011-01-15 22:36 +0000, Tony
> Houghton wrote:
> > I wonder whether it might be possible to use a more
> eonomical card
> which
> > is only powerful enough to decode 1080i without
> deinterlacing it and
> > take advantage of the abundant CPU power most people
> have nowadays to
> > perform software deinterlacing. It may not be possible
> to have
> something
> > as sophisticated as NVidia's temporal + spatial, but
> some of the
> > existing software filters should scale up to HD
> without overloading
> the
> > CPU seeing as it wouldn't be doing the decoding too.
> It's possible, but realtime GPU deinterlacing is more
> energy-efficient:
> - For CPU deinterlacing, you'd need something like
> Greedy2Frame or
> TomsMoComp. They should give about the same quality as
> Nvidia's temporal
> deinterlacer, but the code would need to be threaded to
> support
> lower-frequency multicore CPUs.
> Yadif almost matches temporal+spatial in quality, but it
> will also be
> about 50% slower than Greedy2Frame.
> - Hardware-decoded video is already in the GPU memory and
> moving
> 1920x1080-pixel frames around is not free.
> - Simple motion-adaptive, edge-interpolating deinterlacing
> can be easily
> parallelized for GPU architectures, so it will be more
> efficient than on
> a serial processor. For example, GT 220 can do 1080i
> deinterlacing at
> more than 150 fps (output). Normal 50 fps deinterlacing
> only causes
> partial load and power consumption. GT 430 is currently
> worse because of
> an unoptimized filter implementation:
> http://nvnews.net/vbulletin/showthread.php?p=2377750#post2377750
> Still, only the latest CPU generation can reach that kind
> of performance
> with a highly optimized software deinterlacer.
> > 
> > Alternatively, use software decoding, and hardware
> deinterlacing.
> GPU video decoding is very efficient thanks to dedicated
> hardware. I'd
> guess that current chips only use about 3 Watts for
> high-bitrate
> 1080i25.
> Also, decoding and filtering aren't executed on the same
> parts of the
> GPU chip. They are almost perfectly parallel processes, so
> combined
> throughput will be that of the slower process.
> > Somewhere on linuxtv.org there's an article about
> using fairly simple
> > OpenGL to mimic what happens to interlaced video on a
> CRT, but I don't
> > know how good the results would look.
> Sounds like normal bobbing with interpolation. Even if it
> simulates a
> phosphor delay, it probably won't look much better than
> MPlayer's -vf
> tfields or the bobber in VDPAU.
> Sharp interlaced (and progressive) video is quite flickery
> on a CRT too.
> > BTW, speaking of temporal and spatial deinterlacing:
> AFAICT one means
> > combining fields to provide maximum resolution with
> half the frame
> rate
> > of the interlaced fields, and the other maximises the
> frame rate while
> > discarding resolution; but which is which? And does
> NVidia's temporal
> +
> > spatial try to give the best of both worlds through
> some sort of
> > interpolation?
> Temporal = motion adaptive deinterlacing at either half or
> full field
> rate. Some programs refer to the latter by "2x". "Motion
> adaptive" means
> that the filter detects interlaced parts of each frame and
> adjusts
> deinterlacing accordingly. This gives better quality at
> stationary
> parts.
> Temporal-spatial = Temporal with edge-directed
> interpolation to smooth
> jagged edges of moving objects.
> Both methods give about the same spatial and temporal
> resolution but
> temporal-spatial will look nicer.
> --Niko
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My experience with an nVidia GT220 has been less than perfect. It can perform 
temporal+spatial+inverse_telecine on HD video fast enough, but my PC gets hot 
and it truly sucks at 2:2 pulldown detection. The result of this is when 
viewing progressive video encoded as interlaced field pairs (2:2 pulldown), 
deinterlacing keeps cutting in and out every second or so, ruining the picture 

IMHO the best way to go for a low power HTPC is to decode in hardware e.g. 
VDPAU, VAAPI, but output interlaced video to your TV and let the TV sort out 
deinterlacing and inverse telecine.

I have experimented using FFMPEG and OpenGL and I achieved a very good quality 
picture on a 1080i CRT monitor (I have yet to try an HDMI flat panel TV).

These are the key requirements to achieve interlaced output:

Get the right modelines for your video card and TV.
Draw interlaced fields to your frame buffer at field rate and in the correct 
order (top field first or bottom field first).
When drawing the field to the frame buffer, do not overwrite the previous field 
still in the frame buffer.
Maintain 1:1 vertical scaling (no vertical scaling), so you will need to switch 
video output to match the source video height (480i, 576i or 1080i).
Display the frame buffer at field rate and synchronised to the graphics card 
vertical sync.
Finally, there is NO requirement to synchronise fields, fields are always 
displayed in the same order they are written to the frame buffer, even if 
occasionally fields are dropped.

This can be applied to both interlaced and progressive video so you don't have 
to switch between interlaced and progressive output modes, except you will need 
to make sure you perform colour space conversion to separated fields for 
interlaced material and colour space conversion on whole frames for progressive 

I believe using this approach you could use low power hardware such as ION or 
AMD Sempron 140 with 785G chipset for top quality set-top box style SD and HD 

I can't comment on HD audio. That's a more complex requirement.



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