I thought folks might like to know about a little testing I have been doing.

I know that USB 2.0 does not support more than one HD camera feed per USB channel.

What I didn't realize was that a USB 3.x port actually has both a USB 2 and USB 3 circuits in each channel, sort of side by side.

So it's more accurate to say that you can't put more than one USB 2 camera on a circuit.

However, with a USB 3 hub it's possible to have both a USB 2 camera (e.g., a Logitech webcam) AND a USB 3 capture device (e.g., a Magewell HDMI->USB3 dongle), and vMix is happy with both cameras. I used the Magewell adapter with a Sony FDR-x1000v action camera's HDMI output, but could have just as well tested with a camcorder attached to the dongle.

So far, I've only tested at 720p, as that's my target resolution for Zoom or Skype, but I'll get around to testing 1080p eventually.

For your entertainment... my Toshiba notebook computer (i7 quad core, 8gb ram, etc.) is configured as such (a total of 5 wired cameras)

USB 2 port ->
- Logitech c910 webcam
USB 3 port -> USB 3 powered hub->
- Logitech c930e webcam
- Magewell HDMI to USB3 - > Sony ActionCam FDR-x1000v
- R2 wireless keyboard receiver adapter
USB 3 port -> USB 3 powered hub->
- Logitech c920 webcam
- Plantronics D100 DECT transceiver adapter
- Korg nanoKontrol2 MIDI controller

...and of course, the camera built into the lid of the computer makes 5 camera inputs...

Add to this an NDICam or two running on iPhones, and you can see how this is a pretty powerful little system.

At the moment, the only other USB 3 capture device I have is a Blackmagic Intensity Shuttle, and I might get to test it on the USB 3 channel with the c920, but I have never had much luck with that adapter on this machine... hence my move to the Magewell.

The key here is understanding that in a USB 3 port, one can host a USB 2 camera alongside a USB 3 camera.
I don't know how two USB 3 devices will behave on one USB 3 port, and or if they can be combined with a USB 2 device on that same circuit.

I don't know how long we will have to wait before we see real USB 3.x webcams become available, but for now, this setup is working nicely for me.

This is a little misleading. You can, and I have, put more than one webcam on a USB 2 channel...in HD even. What matters is how you have vMix encode the video streams across the USB connection.

Most webcams will default to sending uncompressed (YUY2) frames which limits the connection to one 720p30 stream.

With some webcams (your Logitech C910 I think) uncompressed is all that you can do.

If your webcams support MJPEG (UVC 1.1 - Logitech C920, C925e, C930e, PTZ Pro, CC3000e, AVer CAM520, AVer VC520) then use that you can have several cameras on the same USB 2 channel. MJPEG delivers about 20:1 compression with no latency.

If your webcams support H264 (UVC 1.5 - Logitech C930e, C925e, PTZ Pro, CC3000e, AVer CAM520, AVer VC520) you can use that encoding. However, being a compression scheme based upon compressing a group-of-frames, it adds considerable latency. Quality is good, but I see 1-2 sec delay in my experiments. May be fine for some applications, unacceptable for others.

The ability to do 1080p30 over USB 2 depends upon using compression over the USB connection. It can't be done otherwise.

There are real USB 3 webcams from companies like PTZ Optics. However, all that gets you is the ability to send uncompressed to the host. There may not be much advantage to that in many cases.

You're better off making the appropriate source encoding settings for each camera in vMix.

Mjgraves,

Thanks for the encoding information... the more we all know about the options, the better.
I will try experimenting with some variations.