Audio Lags on Video Calls

A few weeks ago, I got a new work laptop — a 13” 2020 MacBook Pro. It was pretty easy to migrate from my old laptop (which I was able to buy as a home machine) and has mostly worked without any problem. But one annoying exception was that I started to get some very annoying audio problems on my oh-so-frequent video calls. I’d lose occasional syllables when people were talking, and when interacting I realized there was a lag of about 4 seconds in the audio. This lag really messes up conversation. After some investigation I think I’ve narrowed it down to the interaction with the camera on my Apple Thunderbolt Display causing the VTDecoderXPCService to do a lot of work. I don’t have a fix for this, but am noting what I know here in case others find it useful.

When I noticed the lagging happening, I fired up Activity Monitor to see what was going on, and saw that a process called VTDecoderXPCService was taking up around 20% of CPU when I was on a Zoom call. When I stopped the call, it dropped down to low levels. If I tried to kill it, another one appeared again. My old laptop didn’t have any problems with Zoom, and didn’t show this process using hardly any CPU.

My setup at home is to plug my laptop into an 27” Apple Thunderbolt monitor which I’ve had for many years. As well as being a monitor, it also provides wired Ethernet and USB ports for my keyboard and mouse. Its camera and mic work well for calls, and the big display is needed when I’m on a call with plenty of colleagues. For a while I swapped my old laptop for Zoom calls.

I tried the new laptop on Zoom on its own, and had no problems with the audio and VTDecoderXPCService was low. Experimenting further I found that VTDecoderXPCService popped up when I switched the camera for the call to the camera on the Thunderbolt monitor. Switching the camera to the one on the laptop caused VTDecoderXPCService to drop down and the audio was fine. I can leave the audio for the call on the monitor without any ill effects. I also got the lag and VTDecoderXPCService happening when I used Google’s video service, so I think it’s an issue with MacOs, and not something specific to Zoom.

The new laptop doesn’t have a thunderbolt port, so I connect to the monitor using Apple’s adapter.