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Cockmaster
Feb 24, 2002


I've got a little robotics project going where I'm trying to get a robot to play games on a tablet (either Android or MS Surface). Part of this would mean recording the video off the screen and performing simple computer vision operations (text recognition and template matching, nothing fancy). This could be accomplished by pointing a webcam at the screen, but I was wondering if it would instead be possible to plug the tablet's HDMI output into some sort of USB capture device instead (mostly because I wouldn't have to worry about the robot getting in the way). I've seen a number of things on the market that look like they might do the job:

https://www.newegg.com/Product/Product.aspx?Item=9SIA6ZP3S61171&cm_re=hdmi_capture_card-_-1A0-003U-00003-_-Product

https://www.amazon.com/DigitNow-Cap...Z3X5BF13TJ4G943

Except I don't know if it's actually possible to access them from an OpenCV program as one would a webcam. Is it? If so, how would I do it?

Also, does anyone know which devices are worth buying? I'm just looking for an inexpensive, reliable gadget to get video, I don't need any extra features. Though I would ideally like something that would work under either Windows 10 or Linux. Thank you.

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craig588
Nov 19, 2005

by Nyc_Tattoo


Is latency important? Like the difference in 100ms and 10ms. I see most people using Elgato or Avermedia devices, but I think it's more because they can get an image out in less than 16ms, not because they're any better beyond that. I'm almost sure the cheaper ones will work generally just as well and if some latency doesn't matter they might not be any different. USB can also be annoying because some USB 3 controllers don't work with some capture gear, but if you only need like 480P that might sidestep that issue and work over USB 2.

I can't say always, but one of the common ways capture devices show up to a PC is as a webcam putting out the raw feed they're capturing. I don't know about programming, but if you're already able to see a web cam in your app then it shouldn't be a jump to move to a capture card.

craig588 fucked around with this message at 14:00 on Oct 28, 2017

Cockmaster
Feb 24, 2002


craig588 posted:

Is latency important? Like the difference in 100ms and 10ms. I see most people using Elgato or Avermedia devices, but I think it's more because they can get an image out in less than 16ms, not because they're any better beyond that.

30-40ms would probably be manageable, but 100ms is pushing it. Do you know if the Avermedia Live Gamer Extreme is one of the ones that shows up as a webcam? Thank you.

ufarn
May 30, 2009


I'd hit up the LP tech support thread.

Cockmaster
Feb 24, 2002


craig588 posted:

I can't say always, but one of the common ways capture devices show up to a PC is as a webcam putting out the raw feed they're capturing.

Yeah, upon further research I've found the technical term for that - UVC (USB video class):

https://en.wikipedia.org/wiki/List_of_USB_video_class_devices

Has anyone had any experience with the Magewell 32060? It looks like what I would need to get my project working properly:

https://www.amazon.com/dp/B06Y5RR7XZ/_encoding=UTF8?coliid=I193KAG78D558Z&colid=1RJX1RP6VGLG3

Filthy Monkey
Jun 25, 2007



What OS is your robot running? If you are doing this on something like a pi with a network connection to the device, you would probably be better off just connecting with screen sharing software like VNC. If VNC won't work on your target, you could consider something like mjpg-streamer. Latency might be rough either way though.

Filthy Monkey fucked around with this message at 02:19 on Oct 31, 2017

Cockmaster
Feb 24, 2002


Filthy Monkey posted:

What OS is your robot running? If you are doing this on something like a pi with a network connection to the device, you would probably be better off just connecting with screen sharing software like VNC. If VNC won't work on your target, you could consider something like mjpg-streamer. Latency might be rough either way though.

The robot computer would be running either Windows 10 or Linux (possibly on a Jetson board, or some other single-board system), though either way I wasn't planning to have any network communication between that and the tablet.

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SlowBloke
Aug 14, 2017


We use epiphan AV.io HDMI capture devices for our main conference room, they expose the HDMI input as a webcam which i suppose is what you want

https://www.epiphan.com/

They are not cheap tho.

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