[mythtv-users] RE: nvidia new drivers hdtv/interlacing, any benefit for us non HDTV people?

Bruce Markey bjm at lvcm.com
Sun Jul 4 22:19:49 EDT 2004

Chris Vargas wrote:
> --- bjm wrote:
>>>If I'm understanding things correctly, interlaced 
>>>TV Out (via composite or s-video) should be very 
>>It's not a matter of it might be "useful", it is a 
> Sorry, let me rephrase. I do understand that
> ultimately, the signal going out of the TV out has to
> be interlaced in order to work correctly. We're not
> talking progressive scan HDTVs here, we're talking
> interlaced.

Correct, agreed. However, some people do have HDTVs and they
are now able to benefit from the new support for interlace
modes from their video card's normal monitor out to the
interlace modes that their HDTV supports. This is what was
fixed in the new driver. Nothing has changed for the NTSC/PAL

> The thing that is apparently not happening, is that
> the drivers (or the video circuitry of the card
> itself, or both) are not letting the interlaced signal
> _pass through_ to the interlaced output of the card.

See the rest of my previous replay. The recorded scan lines
are not simply displayed on the same scan line during playback
because even at 640x480 the image is being rescaled to fit in
the underscanned display area which is something less than 480

> Therefore, fields are not being maintained, and
> therefore the video image is affected. Some people
> seem to be able to see this, some don't. 

Placebo effect. Some people convinced themselves that the nVidia
driver didn't "do" interlace and that the new driver "fixed"
interlace so now they have to believe that the new driver is
better. Fact is that the NTSC (or PAL) TV mode is the same as
it was in previous versions of the driver.

> Again, at least with the PVR-x50, the fields are
> definitely there and maintained.

Um, capture of the input signal? The 250, 350, bttv cards,
Matrox, saa7134, cx88 drivers recording at Nx480 all capture
all lines of both fields into a frame. No difference here.

> I think what many
> people see as "better quality" with the PVR-350's
> video out is probably its ability to passthrough
> interlaced video properly.

It outputs 480 lines on 480 lines and updates the frame buffer
during the vertical blank interval in hardware. Software frame
timing is subject to the kernel scheduler so the the process
is not garunteed to have the CPU at the time the frame should
be updated but that's a different issue that affects playback
which isn't interlace per se.

--  bjm

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