AV Nuggets - Sending Laptop Video via a USB C HDMI Adapter to an SDI Adapter: Problem and Solutions
In my AV career, I have discovered a lot of little quirks in the field that I could not find any documentation of anywhere else on the internet. I have decided to document it all through this series “AV Nuggets.” The title refers to the nuggets of knowledge I will share and also a reference to the great DankPods. He calls all the old, terribly made mp3 players he plays with “nuggets.” And I think it is such a good name for the oft frustrating devices that we are forced to work with on a day-to-day basis.
My personal sisyphian struggle is dealing with USB C to HDMI adapters, mostly used with USB C only MacBook Pros. In my current (soon to be former) AV position, I am often tasked with setting up a podium video feed that sends to the front-of-house switcher. This requires an HDMI to SDI adapter (we usually use Decimator HD-LXs) to send that feed to the tech table. This set up works perfectly in all situations except one: when I need to use a USB C to HDMI adapter. For some reason, the output from these adapters do not output enough signal, and the transmitting adapter constantly drops HDMI signal from the adapter, resulting in a flickering image. Nothing fixes it: using a scaler on a decimator, changing the output resolution and dimensions. Annoyingly, using the HDMI port built into the device works perfectly finely . I have not found a reason why this could be happening. If I were to guess, it has to do something with the conversion to HDMI from Display Port.
The official video over USB C standard is called DisplayPort over USB-C. Video over USB-C follows the DisplayPort standard, not HDMI. These HDMI dongles, I am guessing, is converting to HDMI from Display Port internally. This is why the pure HDMI output works while the adapters do not. While this conversion works well enough for consumer purposes (plugging directly into an external display) it is not sufficient enough to work with professional video distribution systems i.e. SDI. Another explanation perhaps lies with HDCP. Regardless, there is an issue and I need to find a solution.
Luckily, I have! Some recommended solutions on the internet (and from my soon-to-be-former manager) involve using a Decimator MD-HX with its built-in scaler to solve the problem. This does nothing and the problem persists (despite my soon-to-be-former manager trying and failing to solve the problem in the exact manner and still insisting the “big decimators” are the solution). The decimators are not receiving a clean signal from the HDMI dongle. It cannot do anything if the decimator isn’t receiving a signal!!!
Probably most people working in the AV industry are familiar with the Blackmagic ATEM Mini switchers. They are designed to take HDMI input from computers due to the gamer-focused streaming focus of the device. They also output nice and clean HDMI that decimators take with no issue. My main way of solving this issue is to place an ATEM between the dongle and the SDI adapter. This solves the dropout issue with ease. My other solution requires the use of an Thunderbolt Dock. Again, the thunderbolt docks with a dedicated HDMI port outputs full fat HDMI. This does not give decimators any trouble in my experience. The issue with that solution is that not every laptop has thunderbolt and because of that it is not a sure fire way to output video. The ATEM solution always works.
Learn from my mistakes and have an extra ATEM ready for a podium laptop. It may seem like overkill but it is not all that expensive. A standard ATEM mini is around $150 used, which is only $50 more than a small decimator. It is pretty compact too! If anyone else has any recommendations on solutions to this problem, I am all ears.