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

Ken VanDine ken at
Wed Mar 19 18:36:08 UTC 2003

This is great info, but I can't seem to capture above 320x240.  I have a WinTV 
Go on a P4 1.5G system.  I try anything higher than 320x240 the quality gets 
worse.  It appears to be capturing at 320x240 and scaling up.  Do you think 
that is what is happening?  I would really like some guidance.  Is it possible 
to force it to not use overlay mode?  

Any help would be appreciated.


Quoting Unit3 <unit3 at>:

> 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...
> >  
> >
> I believe that someone had a good idea about deinterlacing which would 
> be adequate.
> >Can someone clarify why all the specs state 320x240 for many of
> >these cards and where the confusion comes from?
> >  
> >
> I think I can actually answer this! ;)
> When trying to find better software for my TV Wonder under Windows, I 
> found some documentation that basically said that if you were using the 
> video overlay mode of your video card for display, the card could only 
> capture one field of the incoming video, but not both. Essentially, 
> limiting the maximum vertical resolution to 240 pixels. The 
> documentation suggested that it was easily possible to capture both 
> fields if you didn't use overlay mode directly from the card, but 
> instead captured both, did some processing, and then output the result 
> back to the screen (which is what MythTV, Descalar, and WinDVR all do). 
> However, most companies who make these cards would like them to run 
> smoother on lower end systems (for purely marketing reasons I'm sure), 
> and so their supplied software uses overlay mode for display and is 
> limited to 240 vertical pixels. Not suprisingly, most companies then 
> also limit their software to capturing 320 horizontal pixels, since 
> capturing at 640 or 720x240 would be just silly. :)
> I hope this makes some amount of sense. Also, I don't know if this "can 
> only capture one field when using overlay" issue is simple a windows 
> driver issue, a WDM issue, or a chipset issue. All I know is that it 
> does exist under Windows, as even generic DirectShow capturing software 
> will refuse to capture full frames when using video overlay. (I know, 
> I've tried)
> Graeme
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