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using blackmagic card to output live video stream from quartz composer, jitter, etc.
I’m doing a bit of experimental work with live video manipulation using programs like
Quartz Composer
Max/MSP?/JitterI’d like to use the Decklink card as a way of outputting the video. I can set up a preview screen in both applications to run on a video screen through the decklink card but it only runs at a reduced framerate when compared to running it on my Apple Display. I’m getting closer to 15fps than 25fps.
I guess I’m currently writing to the screen using it as a ‘video desktop’ rather than outputting to it like FCP does.
I need to talk to the card like FCP does.I know you can’t look at all the software out there but my question is:
Is there any reason why I shouldn’t be able to feed a live video stream to the decklink card from one of these apps?
Even if it means getting someone to write some kind of code to provide the decklink with a steady 25fps stream of data.Not imagining this will be easy, just want to know if there’s any intrinsic problems.
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7 Replies
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Hi Marcus,
[marcuslyall] “I guess I’m currently writing to the screen using it as a ‘video desktop’ rather than outputting to it like FCP does.
I need to talk to the card like FCP does.”Yes, talking directly with the card is what you need to do if you want smooth video. The video desktop is a nice feature but is something you should only use if desperate as it is likely to lead to jerky video. It’s nice if you want to output from something like PowerPoint as it has no way of outputting directly to the card. If you’re writing your own application, then it would be best to use QuickTime output components so you can output directly to the DeckLink card.
This is the great thing about QuickTime, and the Apple web site has a load of information about how to interface to QuickTime. You need to check the section about writing to an output component. This is how software asks QuickTime to play to hardware. It’s a very nice architecture, as once you get this working, you will work with DeckLink, DV and any other hardware card that’s QuickTime compatible.
There is also a section on writing capture components, and this is how application software can capture from any QuickTime based hardware device without needing to know the details of the hardware device itself. QuickTime does a lot for you already.
Please check: https://developer.apple.com/quicktime/.You might also like to join the Blackmagic Developer Mailing List where you can ask questions if you are having problems making this work. Developers ask questions about QuickTime and DirectShow on the list and you will usually receive replies from other DeckLink developers or our engineers.
Regards,
Luke Maslen
Blackmagic Design -
OK. I’m already using an output component as it is. It’s just that it’s outputting more like After Effects ram preview, where you get a slight stutter or tearing rather than super-smooth.
I’ll check the developer lists and see what’s going on.
Thanks for the swift and detailed reply.
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Couldn’t link to the list in your post.
Will try
https://lists.blackmagic-design.com/mailman/listinfo/bmd-developer
Is this the same one or has it moved?
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Hi Marcus,
Sorry for the bad link. I’m not sure how I managed to do that! I was trying to direct you to the support note on our site for developers named Is there an SDK or API for developers with DeckLink cards?. It includes the link you have already found and that is the right one for signing up on the list.
Regards,
Luke Maslen
Blackmagic Design -
cheers mate.
I’m actually just up the road from you guys (Windsor) , so maybe I’ll see you around the traps.
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jit.qt.videoout
Tig
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Yep. That’s what i’m using.
But I’m not getting a stable 25fps. There’s tearing on the screen. Not much advice on the Max list either.
It’s the same sort of thing you get in AE during video previews where it’s not playing back an absolute 25fps. I’m trying to work out whether it’s an intrinsic problem with working with live video on a computer.
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