Lowest possible latency for camera Image Magnification?

#1

Hi everyone - I’m new to VDMX and excited to get started. My gigs will always involve some camera image magnification and I’m curious if anyone has figured out how fast VDMX can be - and what hardware is required to eliminate any pesky delay?

Here’s one data-point: I see 108ms delay for the following gear and VDMX5:

Black Magic UltraStudio Mini with Marshall CV-150M SDI camera at 720p60 into a Black Magic UltraStudio Mini SDI Thunderbolt adapter. 2015 MacBook Pro AMD Radeon R9 M370X, Quad Core i7 2.8GHz.

HDMI connection to an Asus PA279 monitor.

About 20 of that 108ms is on the HDMI/monitor side.

It takes 62ms for the camera image to make it over SDI, through the Black Magic Thunderbolt adapter, into Black Syphon and then be displayed in the Simple Syphon Client window.

So a 108ms delay is pretty quick but noticeable by most people. Has anyone seen a faster response? I’ll be upgrading to a new MacBook Pro shortly, and curious if that huge increase in CPU/GPU will actually translate into a faster response on the screen.

Thanks!

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#2

I’m not sure about VDMX because I don’t have a way to test the ms, but I’ve found this write up to be useful when searching for UVC (USB 3.0) capture cards: https://obsproject.com/forum/resources/capture-card-documentation-latency-decode-modes-formats-more.777/

Depending on the device you use, you could buy a mokose and get 63ms. I still have to compare it to the iEi HDB-301R that I have. If you need SDI, Mokose also makes an SDI version.

All that being said, I’ve tested a lot of UVC capture cards, some junk, some great. The latency obviously depends on the hardware, but I haven’t seen a latency different between VDMX, Madmapper, or OBS studio when using the same devices. My Mac and PC basically see these devices similar to a USB web cam.

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#3

Thanks very much for that link. That Mokose U70S looks worth a try. For timing the latency I’ve found capturing a camera flash (very quick bursts) in slow-mo on camera phones works well. At 240fps you can be sure of pretty accurate readings if you average several tests.

Another note: I see the tests posted on obsproject.com were using the preview window for the timings. I know of at least one case where that’s not representative: The Black Magic Preview interface on Mac is significantly delayed (~60ms) past when the captured image appears in a Syphon client.

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#4

Use the VV test pattern layer source to display the patch time, then you can actually see how many frames you lose in processing if you point the camera at the patch time.
Do you need to use Syphon to bring the Blackmagic signal into VDMX? This is an extra processing stage and will always add complexity/latency.
Using Blackmagic hardware in a live setting, we average 8-9 frames round trip from the Mac Pro display, through the LED screen processor, and back through the input cards to the display. Without the LED processors and just outputting locally it is around 4-5 frames.

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