[mythtv-users] Re: Capture Card Resolution

Bruce Markey bjm at lvcm.com
Wed Mar 19 12:55:01 UTC 2003


Ray Olszewski wrote:
> My understanding too is that cards like the WinTV series can capture up 
> to 720x384 or thereabouts (whatever the full PAL resolution is, a bit 
> higher than the full NTSC 640x480); I'd certainly believe 720x480 is 
> possible, though I can't vouch for it.

PAL half interlaced frames are 288. The max PAL/SECAM 25 fps
is 768x576 for the bt878 chips.

> The 320x240 (for NTSC) limit is often a practical one, set by the CPU's 
> processing speed and hard disk transfer rate. (And the fact that actual 
> NTSC signals consist of 59.94 fps, composed of interlaced pairs of 
> 320x240 images.)

I agree with everything that you say except the last comment.
While there are a finite number of scan lines, each scan line
is an analog wave. I don't believe there is anything in an analog
NTSC signal which defines a digital width. When digitizing the
analog signal, what determines that horizontal resolution is
clocking when to sample the signal. The horizontal resolution
could be sampled at any arbitrary rate. The bttv driver accepts
multiples of 16 up to the maximum width.

--  bjm





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