[mythtv] Capture Card Resolution -- was: Re: [mythtv-users] 2 Capture card questions

Bruce Markey bjm at lvcm.com
Wed Mar 19 12:27:14 UTC 2003

Brian Foddy wrote:
> Thanks for the reply, but I don't think your proof is valid.  I'm sure
> the Myth will replay whatever resolution it thinks its capturing, but
> that says nothing to what the card is delivering...

This wasn't offered as a proof as you suggest but simply a
way of displaying the pixel for pixel resolution that is in
the file. MythTV doesn't 'think', it encodes the frames that
are mmapped from from bttv driver. The driver 'delivers'
frames that are the dimensions that were requested in ioctls
through the v4l interface.

The suggestion that somehow the capture mistakenly recorded at
a different resolution than the card delivered is bizarre. But
if you want proof that there is more information than 320x240,
consider the following. Turn off deinterlace. See the jagged
edges of things in motion? That's because it is grabbing both
halves of the interlaced frames. There are 480 unique scan
lines in a full frame. For horizontal resolution, grab a frame
with xawtv, display it and use xmag to blow it up. Single pixels
are unique in the 640x480 image.

> Can someone clarify why all the specs state 320x240 for many of
> these cards and where the confusion comes from?

No. No one can explain the unreferenced documents that you
vaguely allude to which you believe you saw. Anything that
suggests that a bt878 is only capable of 320x240 is either
wrong or is being misinterpreted. Google bt878 720x480 to
find dozens of references.

--  bjm

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