Hi Folks We are developing a streaming system which uses MediaRecorder with timeslice. It's clear that Safari only has MediaRecorder as developer experiment, and that older versions of Safari dont support timeslice anyway. However, a recent WebKit thread https://bugs.webkit.org/show_bug.cgi?id=202233 <https://bugs.webkit.org/show_bug.cgi?id=202233> Suggests that timeslice *is* implemented in Safari 14.0.2 and the author provided an example jsfiddle: https://jsfiddle.net/hdwc2xzL/ <https://jsfiddle.net/hdwc2xzL/> Our experience suggests all is not as expected: On Big Sur (on Apple DTK) - Safari 14.02 (with mediarecorder enabled in experimental features) does appear to work as expected. MediaRecorder and timeslice all correct. On macOS Mojave (on MacBook Pro intel) - Safari 13 - (with mediarecorder enabled in experimental features). MediaRecorder initialises OK and works as expected (but without timeslice callbacks) - Safari 14.0.2 (with mediarecorder enabled in experimental features) Throws an error when initialising MediaRecorder "NotSupportedError: The MediaRecorder is unsupported on this platform” Both our own mechanism. and the jsfiddle referenced above shows the same error; try { mediaRecorder = new MediaRecorder(window.stream, options); // options is just {videoBitsPerSecond: 1500000} - hence allowing default mimetype, window.stream successful from getUserMedia } catch (e) { console.error('navigator.getUserMedia error:', e); errorMsgElement.innerHTML = `navigator.getUserMedia error:${e.toString()}`; // fails: "NotSupportedError: The MediaRecorder is unsupported on this platform” } so we dont even get as far as calling mediaRecorder.start(timeslice_ms) any more (as we did with Safari 13) Could anyone explain this behaviour in Mojave ? Should MediaRecorder work on the official shipping 14.02 downloaded on Mojave ? On a related note - what should we expect from mobile Safari with respect to timeslice MediaRecorder ? When might we see MediaRecorder enabled by default so we can use it for customer applications ??? Many Thanks !