Audio lags, only while using video. Accumulates lag as call goes on

I’ve seen other reports about audio lag, but not this issue in particular so I feel that it’s important to point this out anyways.

First, my setup:

  • iPad mini 4, all software is up to date.
  • Internet: house wifi, 802.11n, 3 meters away from the AP in a straight line
  • Place: Santiago, Chile.

Second, what I see:

  • If I’m on a call,
  • And I have video + audio,
  • Audio lags behind video.
  • Lag grows over time.
  • We’ve tested up to 40 seconds of lag.

How it starts:

  • Any time I’m using video and audio.
  • Starts with 1-2s of lag, and the lag keeps growing as the call goes on.
  • Takes 2-5 minutes to be beyond 20s.

How it stops:

  • When I cut the video stream, my audio stream comes back to the present.

What is extra weird about it:

  • Video seems to keep its lag constant. It drops frames, gets visual artifacts, etc, but its lag does not seem to accumulate like the audio lag does.

What I think might be happening? I think it’s got to do with what the server, or the iOS app, is prioritizing. When I’m using video, its main priority is to keep the video fluid and in the present, but it optimistically tries to send ALL of the audio, even if that results in more and more lag from having a lower quality connection. When I’m using audio, its priority shifts towards keeping the audio fluid and in the present, and thus never accumulates lag.