jit.qt.grab is capturing with lower resolution than jit.dx.grab

Feb 14, 2010 at 6:59pm

jit.qt.grab is capturing with lower resolution than jit.dx.grab


With the new blackmagic intensity card and experiments on both mac and windows systems, it seems that the jit.qt.grab object captures not as well as its counterpart, the jit.dx.grab. maybe this has not been observed so far because the normal webcams and pal (or ntsc) videocams send lower resoltions than this new capturecards. however, I attached a screenshot of my patch, and provide here the patch itself. This patch has the same effect on windows and mac, while jit.dx.grab captures just fine.

can anybody confirm this?

– Pasted Max Patch, click to expand. –


  1. 720pGrabCapturing.png
Mar 25, 2010 at 3:03pm

The basic answer is avoid jit.qt.grab on windows. The implementation of the third party vdig components for jit.qt.grab on windows is not great.

Mar 25, 2010 at 5:35pm

interestingly enough jit.qt.grab shows the same (above mentioned) result on OS X.

Mar 25, 2010 at 5:58pm

Hmmm…it might be something about the black magic card’s preview mode delivering lower resolution frames. Does it capture to direct to disk with better resolution. Have you tried different vmodes (1 or 2)?

Let us know what you find. If this isn’t it, it looks like from your example you are capturing a screen. Is this the blackmagic card’s output display, or is it being sent in the HDMI from another computer?

I might be able to test this next week if I can get a machine with a blackmagic card set up.


Mar 26, 2010 at 11:44pm

Its the screencapture of the above patch, with a jit.pwindow of the same size of the (HDMI – ) captured second screen of an OS X machine.

No, I havent tested with different vmodes yet, and I havent compared it with direct to disk captured images – however here my guess, at least on a windows machine, it would be same result as the capturing with jit.dx.grab, which works fine.

I will make these tests next week and will report back.

Mar 29, 2010 at 7:06pm

I have a positive testresult:

vmode 2 gives the desired result and looks good.

unfortunately I didnt test the performances, and the card is back in the windowmachine again.

thanks for looking into this



Mar 29, 2010 at 11:56pm

Okay, then for that card, you’ll need to use vmode 2. It sounds like for preview, the black magic card uses a lower resolution capture. It doesn’t sound like there’s anything for us to look into at this time.



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