USB-C video capture

[ereiamjh]

Apologies if this is a dumb question.

I can connect an HDMI adapter to the USB-C port on my laptop or my phone. I can then connect that to an HDMI capture device.

Is it possible to eliminate the HDMI adapter and somehow capture directly from the USB-C video stream?

[Cornucopia]

The USB-C spec allows for an alternate mode where it is basically no longer acting as a usb port, but rather as an hdmi port. That is why you can use such a simple adapter as what you have.

You could possibly do what you are intending to do, but if the usb-c port is going to be used AS a usb port, what you would need to be putting out would be uvc (aka "webcam") video. This could be doable, but you would likely need a driver to support that. Don't know of any offhand that support video/screen out like that, sorry. Most likely the driver would have to hook into the OS rendering engine or to pull a feed from the video card buffer.
Also, you would likely need a male<->male usb cable.

All in all, I'd say that the adapter way the you are currently doing is probably the simplest and most foolproof.

Scott

[usually_quiet]

If I recall correctly, the USB C ports that have an HDMI video mode and can supply video via a simple USB C to HDMI cable are actually Thunderbolt 3 ports. The USB 3.1 type of USB C port only supplies data and power and needs a USB C to HDMI external video graphics adapter to provide HDMI video.

[Cornucopia]

I could be mistaken, but this article: https://www.google.com/amp/s/www.theverge.com/platform/amp/circuitbreaker/2016/9/1/127...specifications leads me to believe that the HDMI alt mode is not necessarily limited to Thunderbolt versions of USB-C.
However, if one has the option, the Tbolt3 variety is certainly preferred.


Scott

[usually_quiet]

I looked for more specific information and all I could determine is that the USB C connection itself is capable of both HDMI Alt Mode and DP Alt Mode but they aren't always implemented. I could not find anything that said whether either of the "Alt Modes" is common, rare, or non-existent for the USB 3.1 type USB C ports.

FWIW, I now know that the USB C port on my Motorola smartphone doesn't support an "Alt Mode" and the USB 3.1 type C connections provided by the motherboard on my 2018 desktop PC are not listed in the manual's specs as supporting an "Alt Mode" either.

[Cornucopia]

OK - theoretically possible, but not commonly in practice, unless you use Tbolt3. Good to know.


Scott

[usually_quiet]

I did a little searching for more answers.

First, I misremembered something. A Thunderbolt 3 connection doesn't have the ability to output HDMI directly allowing the use of a simple cable. Thunderbolt 3 only has the ability to supply a display port connection so an active DP to HDMI converter is needed for HDMI out from Thunderbolt 3.

Althoughthe USB C spec includes both HDMI Alt Mode and DP Alt Mode, devices with DP Alt Mode appear to be more common at present. For example, I found specs for a Dell XPS laptop that listed two types of USB C connections, USB 3.1 and Thunderbolt 3 and both types supported DP Alt Mode but not HDMI Alt Mode. Some Chromebook and MS Surface models have a USB 3.1 type USB C port with support for DP Alt Mode but as far as I can tell, none of them includes a Thunderbolt 3 connection. I haven't yet found anything that has a USB-C connection with HDMI Alt Mode but I did find an article indicating that they might exist. https://www.koincable.com/hdmi-alt-mode-usb-type-c/

If someday USB C becomes the predominant connection for data, power, and video on smartphones, computers, and tablets maybe we will see more devices with HDMI Alt mode as well as capture devices with a USB C input. However, I don't expect USB C to replace HDMI on set-top boxes, video playback devices, TVs or receivers.