Bugfix: Reset gap-controller nudgeRetry

[robwalch]

This PR will...

Reset gap-controller nudgeRetry count after playhead moves, pauses, or ends while not seeking.

Why is this Pull Request needed?

When nudgeRetry reaches nudgeMaxRetry, the error is escalated to fatal (expected):

hls.js/src/controller/gap-controller.ts

Lines 334 to 365 in 46a7ca2

	private _tryNudgeBuffer() {
	const { config, hls, media, nudgeRetry } = this;
	if (media === null) {
	return;
	}
	const currentTime = media.currentTime;
	this.nudgeRetry++;
	if (nudgeRetry < config.nudgeMaxRetry) {
	const targetTime = currentTime + (nudgeRetry + 1) * config.nudgeOffset;
	// playback stalled in buffered area ... let's nudge currentTime to try to overcome this
	const error = new Error(
	`Nudging 'currentTime' from ${currentTime} to ${targetTime}`,
	);
	logger.warn(error.message);
	media.currentTime = targetTime;
	hls.trigger(Events.ERROR, {
	type: ErrorTypes.MEDIA_ERROR,
	details: ErrorDetails.BUFFER_NUDGE_ON_STALL,
	error,
	fatal: false,
	});
	} else {
	const error = new Error(
	`Playhead still not moving while enough data buffered @${currentTime} after ${config.nudgeMaxRetry} nudges`,
	);
	logger.error(error.message);
	hls.trigger(Events.ERROR, {
	type: ErrorTypes.MEDIA_ERROR,
	details: ErrorDetails.BUFFER_STALLED_ERROR,
	error,
	fatal: true,

nudgeRetry is reset when polling currentTime. The expectation is that this runs after currentTime has advanced naturally. Note that stalled must not be null - the think here is that this is reset when exiting a stall, but this does not work if stalled is reset before reaching this point:

hls.js/src/controller/gap-controller.ts

Lines 47 to 73 in 46a7ca2

	public poll(lastCurrentTime: number, activeFrag: Fragment | null) {
	const { config, media, stalled } = this;
	if (media === null) {
	return;
	}
	const { currentTime, seeking } = media;
	const seeked = this.seeking && !seeking;
	const beginSeek = !this.seeking && seeking;
	this.seeking = seeking;
	// The playhead is moving, no-op
	if (currentTime !== lastCurrentTime) {
	this.moved = true;
	if (stalled !== null) {
	// The playhead is now moving, but was previously stalled
	if (this.stallReported) {
	const stalledDuration = self.performance.now() - stalled;
	logger.warn(
	`playback not stuck anymore @${currentTime}, after ${Math.round(
	stalledDuration,
	)}ms`,
	);
	this.stallReported = false;
	}
	this.stalled = null;
	this.nudgeRetry = 0;

And here we see that stalled is reset to null before nudging, so nudgeRetry will never be reset:

hls.js/src/controller/gap-controller.ts

Lines 206 to 211 in 46a7ca2

	logger.warn('Trying to nudge playhead over buffer-hole');
	// Try to nudge currentTime over a buffer hole if we've been stalling for the configured amount of seconds
	// We only try to jump the hole if it's under the configured size
	// Reset stalled so to rearm watchdog timer
	this.stalled = null;
	this._tryNudgeBuffer();

Are there any points in the code the reviewer needs to double check?

Resolves issues:

Resolves #5873

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md

[robwalch]

Also related to #5904