[webkit-dev] Webkit MediaRecorder Timeslice functionality on Safari 14.0.2 Mojave

[Gallery]

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 !



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