The main one is that clock synchronization no longer happens on incoming sources, this is not needed because the renderer pipeline is separate and they can't synchronize on the system clock either. So before this patch the clock sync on the first pipeline was artificially limiting the playback on the renderer pipeline.
Pull request: https://github.com/WebKit/WebKit/pull/5998
Committed 256225@main (5adbc713768c): <https://commits.webkit.org/256225@main> Reviewed commits have been landed. Closing PR #5998 and removing active labels.
<rdar://problem/101854535>