Initial frame of AVCaptureSession with AirPods has zero PTS?

When I create a capture session on macOS Catalina with video from the FaceTime HD camera and audio from AirPods the first video CMSampleBuffer presentation timestamp is zero, and the subsequent ones are the more usual hostime type timestamps, which appear to be system uptime.


If you use the first frame PTS to start an AVAssetWriter session, then the duration of the first frame in the resulting file is your uptime! e.g. right now mine is 22 hours, but it could easily be weeks.


Here's a repro https://github.com/gchilds/airpod-pts-bug-repro


A demo: https://www.loom.com/share/c5e6a8a122334bbd92437f87e8491a34


Is this a bug? Or is this somehow my fault?
We're probably going to ignore these otherwise legitimate seeming frames.