Circleback moves its meeting recorder out of the Electron render process to ScreenCaptureKit on macOS and libobs on Windows, bridged to React by a compile-time Swift macro

Sources: Circleback engineering post, HN discussion
Summary: The post, dated 2026-04-16, describes replacing recording inside the Electron render process with two native capture engines, ScreenCaptureKit on macOS and libobs on Windows reached through a Swift wrapper the post calls OBSKit, with a shared Swift layer bridged to the React front end by a compile-time Swift macro. The post states the two engines have fundamentally different architectures, and that the clock-drift and mixer work is macOS-specific because the Windows capture engine abstracts most of it away. It names two failure modes concretely. Audio drivers that report 48kHz while delivering 44.1kHz drift audibly over a 30 minute meeting, which the team corrects by measuring buffer cadence across three consecutive buffers and reinterpreting the stream with a crossfade. Fragmented MP4 makes each segment self contained, so a crash mid-recording does not lose the file. The post is vendor-authored and closes with a hiring pitch.
Why it matters: Fragmented MP4 makes each written segment self contained, so a crash at minute 30 loses at most the last second rather than the whole recording.