Multiple Cams simultaneous real-time acquisition ?
Hi there,
Still in the middle of a big project for which I need to capture 3 webcam simultaneously (swap the one I record (only one at a time).
I found the Decklink Quad HDMI Recorder : https://www.blackmagicdesign.com/products/decklink/techspecs/W-DLK-36
It can drive 4 cam. We'd use 3 Panasonic GH 5 & 4.
We'd need a very tight sync etc.
The PC would be a very big one (i9, 128Gb RAM, BIG RTX for the texture process + replay)
Would this setup the best from the acquisition point of view ?
I read Blackmagic drivers behave well in this kind of setup, with max.
Hello there, I still didn't have any chance to get some answers :-)
We are on it.
jit.dx.grab seems a way to follow VS jit.grab
The issue here is the latency.
- cams => Decklink Quad HDMI Recorder => OBS ====> VERY FAST display (not recording this)
- cams => Decklink Quad HDMI Recorder => Max 8 =====> feeling latency
I can't understand.
We are using a basic patch just grabbing frames with jit .grab, or jit.dx.grab as mentioned.
1080p 25fps (from nice panasonic cams)
By latency, I mean: there is a delay (I guess about 250ms, 300ms)
Hey,
I capture cameras all the time.
Just to get this straight..
You are capturing into the Decklink to record, is this then going live to screen?
Trying to figure out where the latency is noticed?
There will always be latency, no matter what you do.
Can you not record with OBS? If you run the cams at 50 fps, you'll halve the latency.
If running to a live screen, I run everything at 50 fps, capture with Resolume (surprisingly fast) and send via spout to max for processing?
Let me know if I can help further.
B
Hi there.
I'm talking about the delay between a movement in real life and the frames showing the movement on the computer.
Frame reading seems smooth.
Frame rate at reading seems ok too.
But that delay...
I'm not sure adding resolume + syphon in the chain could help (but I obviously don't know as I didn't test myself) VS jit.grab or even jit.dx.grab
And I don't talk about recording. Just... Displaying frame.
I tested with a basic patch. Same.
Decklink here are just the hub. It collects 2 flows. And potentially 4.
I was thinking about creating a switching system for not grabbing all flow at the same time (as only one would be recorded at a time... But I was afraid of small overload when switching a jit.grab on and off on the fly)... But even with one 1080p25i/s, it is the same delay.
The computer is very powerful, I talk about a i9, 128Gb RAM, one BIG NVIDIA RTX.
s
We trying with resolume (and obs) as frameservers through spout in the equation.
OMG, it doesn't work better here !
Current research is about recording a BIG file, constantly, and to trying to find a way to play some part of it (during the recording) in order to grab the correct moment in time and to "offset/remove" the delay.
Hello Julien,
I did a quick test here concerning frame latency.
I sent timecode @25fps from my laptop into my PC using a Blackmagic Decklink Duo 2.
I wasn't able to acquire an image with jit.dx.grab with max? I tried evrything.
Might help..?
B
possibly helpful discussion - https://forum.openframeworks.cc/t/how-to-reduce-latency-when-projection-mapping-onto-moving-objects/42464
Interesting read, thx Rob.
B