Does anyone have experience using vdmx with the AJA io 4k?

vdmx
video-capture

#1

I was looking online for a good low-latency sdi i/o solution for use with my macbook and vdmx. i want to use vdmx in a live broadcast environment, specifically music concerts. either for output to the venue screens or for use in the recording. obvously low latency in this situation is key. It seems the aja io 4k has pretty much everything i need in terms of input/output, but i do not know if vdmx will recognise it and work with it? for instance if i get the audio engineer to send me a specific multitrack so i can build effects that work only on the kick, or snare, or hihat specific channels. so far in the demo version i have to test some stuff all i get in terms of audio i/o is the built in microphone, which would not do.
also the aja has multiple sdi inputs. would vdmx see them and allow me to select them as inputs as well? hope someone has some info on this, the aja’s price tag makes that i would not want to have to buy it in vain. thanks in advance for any suggestions!


#2

We have an AJA io 4k in the studio for testing purposes.

A few notes…

  • Within VDMX it will work for basic usage through AVFoundation as inputs, if there’s any specific tests you’d like us to try out let me know.
  • Beyond that, we’ve been looking into possibly adding native support in VDMX through their SDK, and / or potentially releasing a freebie app similar to BlackSyphon; last time I asked around there wasn’t much demand for it (compared to other new features we can focus on), but we have written a bunch of test code for this already and it might happen at some point.
  • With regard to video outputs, this is something we could do with native AJA support in VDMX (similar to how we support BlackMagic output), however! there is a big gotcha. While these device are handy for doing an ‘extra’ output, there is actually a big performance hit compared to doing a direct output from your graphics card. Since all the video rendering in VDMX takes place on the GPU, images need to be read back to the CPU in order to be sent out by such devices. We we generally recommend against this technique unless absolutely needed; to get the best performance you’d be best off using an HDMI to HD-SDI adapter from your regular monitor outputs.
  • While it might be technically possible to capture multiple audio streams of input through an IO 4k, you might be best off using a more traditional audio interface (see notes below). I say this because the IO 4k does not have any RCA, 1/4" or other audio cable inputs; you’d need some way to attach that multi-track audio along with a video input stream. That might work for your particular needs, but it is generally a pain.
  • If you haven’t already scoped it out, this thread has some discussion around devices that people seem to be commonly using for video capture recently, Video capture devices thread

And as far as multi-channel audio inputs…

  • When it comes to multi-channel audio inputs, you’ve got a lot of options (a quick google search brings up this nice looking comparison, https://www.gearank.com/guides/audio-interface and the top ranked 4-6 channel input interface appears to be only $100)
  • VDMX will work with multiple audio interfaces, so if you get a couple of cheap stereo inputs and a USB hub, that might be your lowest cost option if you are just looking to play around before deciding on a more expensive purchase.
  • Here is a tutorial on using multi-channel audio from app to app through Soundflower (https://vdmx.vidvox.net/tutorials/analyzing-multiple-audio-tracks-from-live-in-vdmx-with-soundflower) and the same basic idea / technique applies when working with external interfaces / multiple interfaces.

#3

thank you for the very detailed response.
-so with the aja io 4k latency is going to be more of an issue than when i would convert the hdmi out from my usb c breakout to sdi? even taking into account the lack of reference input on that breakout as supposed to the aja ref input. (i’m talking about bringing the vdmx output(s) back into the video switcher used for the broadcast).

-if i am not mistaken the aja has a breakout cable for analog audio inputs (xlr). for my purpose this would work, or alternatively the audio can be embedded into the sdi signal (aja io 4k supports 16 channel embedded i believe)

be that as it may, the aja is quite expensive, and spending 3k on a device that is not going to significantly reduce latency seems pointless. 4-6 channels of audio should be enough for my purpose and at $100 that is a much better deal, thanks.
Apparently blackmagic has an external gpu box for macbooks. sadly it also only features hdmi out, and not sdi. hopefully they will make one that does, it seems that would then be the go to solution for low latency io, or am i mistaken?


#4

Ok from the sound of it, you are basically looking to do two different things, and it sounds like the AJA IO 4k isn’t quite what you want for either of them…

Audio Capture

Hm, you might be looking at a different device, but as far as I am aware the AJA IO 4k (https://www.aja.com/products/io-4k#techspecs) does not have an break-out cables or other way to do XLR inputs.
(perhaps the confusion is that the power connector is an XLR head?)
(note that they do offer an optional audio breakout cable for audio output)

On the tech specs page I linked to it says:

Audio Inputs Digital

• 16-Channel, 16 and 24-bit SDI embedded audio, 48 kHz sample rate, synchronous
• 8-Channel, 16 and 24-bit HDMI embedded audio, 48 kHz sample rate, synchronous

Which means that the multi-channel audio is embedded as part of the SDI or HDMI signals for input; there is no way to get other audio signals in through this device.

And if that is the case, it probably isn’t at all suitable for your audio capture needs.

Video Output

I’ll try to be as clear about this as possible – you’ll generally get the best performance and lowest latency if you do an output directly from your GPU; in most cases a basic USB-C to HDMI adapter is all you need. From there you have lots of options for HDMI to SDI adapters.

If you want to do a direct HD-SDI output, you can probably use a BlackMagic Mini Monitor as the lowest cost solution and these are already natively supported by VDMX. These can be useful if you need to add extra outputs beyond what your GPU is capable of via regular monitor outputs. The latency / performance isn’t awful when using these, but I strongly recommend using direct GPU outputs first whenever possible first.

In general we do not recommend using eGPUs if you have the ability to do a direct output from a built-in GPU. Like with using a BlackMagic / AJA device for output, if you have to pass video from one GPU to another for any reason, you can get a performance hit (though latency probably not a big deal here). More about eGPUs in our docs here:
https://docs.vidvox.net/vdmx_gpu.html

(it is also doubtful that you’ll see eGPUs with native SDI outputs on the market anytime soon; again your best bet here is to invest in a decent HDMI to SDI adapter)

Currently the IO 4k is not supported in VDMX as an output device; if we did add support, it would be along the lines of the BlackMagic Mini Monitor in terms of performance / latency.


#5

you are right, thanks again. just saved me from a bad purchase :)

i will look into the blackmagic mini monitor solution for outputting video,
the behringer u-phoria for audio input. a mini recorder for input should do the trick.
When i have all that available i will have a look and see what the delay is after rerouting the signal back into the video matrix for use in a keyer.

thanks again!