Compensate for bluetooth latency

[TobiasBales]

Hey,
I would (personally) love if alphaTab would/could compensate for bluetooth latency - in the browser this can be discovered via AudioContext.outputLatency.
Would this something you would be interested in/willing to support?
If so, and if you could give me a pointer of where a good spot for that might be I'd gladly try my hand at adding support for it

[Danielku15]

That definitely makes sense. I assume with "compensation" you mean effectively that the cursor and advertised "play position" are adjusted with this given latency?

If the outputLatency is not changing it should be fairly easy to add. If it is changing it might be hard to continuously adjust the position but it should be possible.

Techncially I think it makes sense to extend this event:

• https://github.com/CoderLine/alphaTab/blob/develop/src/synth/ISynthOutput.ts#L58

Instead of just passing on the number of samples played, it could pass on a structure containing samples and latency.

class SamplesPlayedEventArgs {
    public samplesPlayed:number;
    public outputLatency:number;
}

Then in the main synth the latency has to be handled:

• https://github.com/CoderLine/alphaTab/blob/develop/src/synth/AlphaSynth.ts#L405-L413

I'd have to also fiddle a bit around to see where exactly the latency should be respected to not break anything on the synthesizer itself. We might need to add new properties to differenciate the "synthesizing" time line and the "heard" timeline.

• alphaTab/src/synth/AlphaSynth.ts

  Lines 459 to 501 in 34ad6af

  	private updateTimePosition(timePosition: number, isSeek: boolean): void {
  	// update the real positions
  	const currentTime: number = timePosition;
  	this._timePosition = currentTime;
  	const currentTick: number = this._sequencer.currentTimePositionToTickPosition(currentTime);
  	this._tickPosition = currentTick;
  	const endTime: number = this._sequencer.currentEndTime;
  	const endTick: number = this._sequencer.currentEndTick;
  	const mode = this._sequencer.isPlayingMain
  	? 'main'
  	: this._sequencer.isPlayingCountIn
  	? 'count-in'
  	: 'one-time';
  	Logger.debug(
  	'AlphaSynth',
  	`Position changed: (time: ${currentTime}/${endTime}, tick: ${currentTick}/${endTick}, Active Voices: ${this._synthesizer.activeVoiceCount} (${mode})`
  	);
  	if (this._sequencer.isPlayingMain) {
  	(this.positionChanged as EventEmitterOfT<PositionChangedEventArgs>).trigger(
  	new PositionChangedEventArgs(currentTime, endTime, currentTick, endTick, isSeek)
  	);
  	}
  	// build events which were actually played
  	if (isSeek) {
  	this._playedEventsQueue.clear();
  	} else {
  	const playedEvents = new Queue<MidiEvent>();
  	while (!this._playedEventsQueue.isEmpty && this._playedEventsQueue.peek().time < currentTime) {
  	const synthEvent = this._playedEventsQueue.dequeue();
  	playedEvents.enqueue(synthEvent.event);
  	}
  	if (!playedEvents.isEmpty) {
  	(this.midiEventsPlayed as EventEmitterOfT<MidiEventsPlayedEventArgs>).trigger(
  	new MidiEventsPlayedEventArgs(playedEvents.toArray())
  	);
  	}
  	}
  	}

I added #1455 as work item to track this feature and added some thoughts there. .