Frequent warnings on playback start

[softworkz]

I'm frequently getting these warnings logged when starting playback:

The warning is emitted in method alignPlaylists:

hls.js/src/controller/base-stream-controller.ts

Lines 1046 to 1056 in a586139

	if (previousDetails && details.fragments.length > 0) {
	sliding = details.fragments[0].start;
	if (details.alignedSliding && Number.isFinite(sliding)) {
	this.log(`Live playlist sliding:${sliding.toFixed(3)}`);
	} else if (!sliding) {
	this.warn(
	`[${this.constructor.name}] Live playlist - outdated PTS, unknown sliding`
	);
	alignStream(this.fragPrevious, lastLevel, details);
	}
	} else {

Is that expected to happen? And what is supposed to be "aligned" in that situation?

There's just a single media playlist and when that method is called, details and previousDetails are exactly the same.

Thanks

[robwalch]

Any idea why the playlist is refreshed 6 times at start without updating? That would have happened before we got here, and at this point, the method alignPlaylists is just surprised that there is a list of fragments starting at 0, that does not need to be shifted.

[softworkz]

Any idea why the playlist is refreshed 6 times at start without updating?

Ah, that's probably due to the fact that I'm delaying/blocking the request for the first segment until data is available (= tuning into a channel at the server side). This can take between 300ms and 3-5 seconds.
It seems that hlsjs is starting operation and timers when sending out the request for the first segment. I would probably need to delay all this until the first segment data has arrived.
Is there any easy way to achieve this?

[softworkz]

delaying/blocking the request for the first segment until data is available

Could this also be the reason for the other issue I'm seeing: #3928 ?

[robwalch]

I really don't know about your particular use-case or if this is directly related to your other issue. I doubt it, at least with respect to the logging.

I've done some cleanup and removed the warning in #3967. What you should see instead is clearer Live playlist sliding: messages with details about the first SN before and after the refresh, and what the SN of the last appended segment was when we do try to align the playlist here.

You can take it for a spin here:
https://deploy-preview-3967--hls-js-dev.netlify.app/demo/

[softworkz]

Thanks Rob, looks good. I'll try shortly (but I can't use the online demo with my local environment, so I'll need to pull/rebase first).

I really don't know about your particular use-case or if this is directly related to your other issue. I doubt it, at least with respect to the logging.

Could you perhaps hint me at the right place(s) where I can block the processing of hlsjs until the first data has arrived (from the first segment request)?

[robwalch]

Could you perhaps hint me at the right place(s) where I can block the processing of hlsjs until the first data has arrived (from the first segment request)?

Block what processing exactly? Playlist reloading (see level-controller and computeReloadInterval largely based on TARGET-DURATION)? More, like level switching (set config.startLevel)?

The components of HLS.js operate independently and in response to events, timers, API methods, and configuration.

[softworkz]

I mean everything that is related to timing - not the video timestamps, but what is used to control hlsjs operation. Playlist can be reloaded as many times as it wants to do - as long as that doesn't trigger anything else.

The result should - ideally - be as if the time while waiting until the first byte of the first segment arrives wouldn't have existed. :-)

[softworkz]

PS: I'm testing your PR right now

[softworkz]

I can confirm that your PR fixes the reported issue.

Thanks again for your great work 👍