Safari plays slow/lagged audio out of sync with video when Safari has been open for a while. Applies to video sources anywhere and all recent MacOS versions.
Occasionally, I will start a video in Safari (from any source, including YouTube, Hulu, Vimeo, Coursera, Khan Academy, etc.) and the video will play normally while the audio plays at an extremely slowed pace, gradually getting very far behind the video. To illustrate the degree; the speed is so slow that pitches are substantially lower; most voices are so low-pitched that few people could possibly speak in that range.
Notably, there are some other discussions that I think express the same issue, and all have been closed with little more than standard browser suggests (like restart or cache). The problem should not happen in the first place, whether or not there are temporary ways to recover from it. See audio out of sync on history channel stre… - Apple Community, YouTube and safari audio sync in videos - Apple Community, and maybe Audio/Video not syncing in the system vid… - Apple Community, for example.
This seems to happen only after Safari has been open for some time. I know that is vague, but in the years I've experienced this, I haven't identified any particular duration or action that triggers this (e.g. number of windows/tabs open, sleep/wake cycles, memory utilization, etc.), and every time it occurs, a restart of Safari fixes the issue for the time-being.
Yes, my reference to "years" means that I've experienced this on multiple MacBook Pro laptops on at least 3 different major versions of MacOS. I am fairly confident at this point that this is a defect in Safari.
MacBook Pro 16″, macOS 14.0
