[rtcweb] A/V sync after audio interruption on iOS

Lydia Sun <lydia@airtime.com> Fri, 04 June 2021 20:13 UTC

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From: Lydia Sun <lydia@airtime.com>
Date: Fri, 4 Jun 2021 13:12:41 -0700
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Subject: [rtcweb] A/V sync after audio interruption on iOS
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Hi all,

I work on the media team at Airtime, a platform for live video chat and
co-watching content.
Our team has come across an audio/video sync issue on iOS -- we are
wondering if anyone else has seen this or has some insight into the problem:

   1. A publisher is publishing audio and video.
   2. The publisher receives an audio interrupt, such as a phone call or a
   timer going off.
   3. The interrupt ends with the phone call rejected or the timer stopped.
   4. After this, the subscriber sees that the publisher's audio and video
   are out of sync.

Our application does not use CallKit, so that for the duration of the
interrupt no audio samples are captured.

Has anyone observed something similar before? If interested, I am happy to
share some other findings that we have collected regarding the behavior of
RTP timestamps and RTCP sender reports surrounding the audio interrupt -- I
am leaving it out here to avoid adding a wall of text.

Lydia Sun
Software Engineer, Media