Feature/v1.0.0 Latency Controller change playbackRate frequently

[mnikn]

Is your feature request related to a problem? Please describe.
Now latency controller will change video playbackRate when (level.edge - currentTime) is more than 0.5s, thus the video playbackRate are hard to maintain in 1, which will cause a poor user experience.

Describe the solution you'd like
Is it possible that add some params to customize latency controller behaviour, eg:

{
  // when (level.edge - currentTime) are more than threshold, it will consider to change playbackRate
  distanceFromEdgeMaxThreshold: number;
  // (level.edge - currentTime) more than threshold time limit duration
  distanceFromEdgeThresholdDuration: number; 
  // when canReduceLatency is false, won't do any playbackRate change
  canReduceLatency: boolean;
} 

The sample code:

let edgeThresholdStartTime = 0;
function checkLatency() {
  if (!config.canReduceLatency) {
    return;
  }
  if (distanceFromEdge >= config.distanceFromEdgeMaxThreshold) {
    if (edgeThresholdStartTime === 0) {
      edgeThresholdStartTime= performance.now();
    }
  }
  if (edgeThresholdStartTime !== 0 && performance.now() - edgeThresholdStartTime >= config.distanceFromEdgeThresholdDuration) {
    doPlaybackRateChange();
  }
}

[robwalch]

@mnikn This will be resolved in an upcoming release with auto low-latency mode. I'll put this issue next to the note in progress in https://github.com/video-dev/hls.js/projects/7

"auto" lowLatencyMode
Switch from part loading with playbackRate adjustment to fragment loading at 1x speed based on currentTime's proximity to the playlists part list.

Since users may want to use the latency controller with non LL-HLS streams I may add another option, or use a value between hls.targetLatency and liveMaxLatencyDuration(Count) to determine when playback rate adjustment kicks in.

Thanks for suggesting canReduceLatency, but I think a distance to edge threshold in seconds, would be a better option, along with an idea for how we could calculate this when the user doesn't specify a value, as a fixed value really wouldn't be appropriate.

[robwalch]

@mnikn there is a fix for this issue in https://github.com/video-dev/hls.js/releases/tag/v1.0.0-alpha.3