[mythtv-users] HD deinterlacing

[Mark Kendall]

On 10/1/07, Phil Vid <phil.vid at gmail.com> wrote:
> Hi List,
>
> Have just got a new HDTV (1080p native) so am trying to get the best
> quality playback from Myth possible.
> I am using a 5200+ dual core athlon with 2gb ram. I am running latest
> SVN (14547) with the displayprofiles, using ffmpeg and xv-blit. NVidia
> 7200 series card with 256mb on board set to 1080p output over dvi. I
> am running the latest nvidia drivers and enabled the rtc kernel param
> which fixed some tearing.

Are you using opengl-vsync as well?

> Using linearblend, the playback seems to be very crisp until motion
> occurs, and then it is somewhat crisp and then jerky every now and
> again. Hard to discern but if you are looking for it, it is obvious.

Linearblend does not double the frame rate when it is deinterlacing.
Hence you only get 25 frames per second. Using a 'frame rate doubling'
deinterlacer (e.g bob) will give you much smoother playback.

You also need to ensure that you have the appropriate display refresh
rate. So assuming you live in PAL land, you need to be running a
1080p50 modeline to best match PAL sources (25 fps) to the display.

> Using bob, it feels like the video is slightly sped up at times. When
> there is no motion, it seems fine but then when a scene change occurs
> it seems like things speed up slightly even though the audio sounds
> fine. Also it appears slightly glittery but this is not so noticeable.

You will get some vertical 'jitter' with bob  - that's the nature of
how it works. It shouldn't however be too noticeable if your display
refresh rate is 'matched' to your source.

The speed issue might be a symptom if you are not using opengl-vsync.

You could also try opengl linearblend (2x HW) or opengl onefield (2x
HW) - but I suspect your graphics card isn't up to it.

The best solution would almost certainly be to use a 1080i modeline
for 1080i material (use xrandr if need be) and get the tv to
deinterlace for you.

If you're lucky, your tv will just sync with the incoming interlaced
material otherwise try the 'Interlaced' opengl deinterlacer which is
designed for this situation. It's a less gpu hungry filter so may just
work with your card.

The main problem you'll find with this approach is buggy nvidia
drivers. I think the latest drivers still haven't fixed interlaced
modelines.

Regards

Mark