WIP: Playback Rate

[NicholasBly]

A highly requested feature is to fix/add support for playback rate (0.25x up to 2x).

I originally attempted this about a year ago, found that it would work on any webOS emulator/simulator, but never on real hardware.

Progress so far:

1. Working settings menu for adjusting playback rate. Starts at "Normal" and left/right arrow can adjust the speed up and down.

2. Playback Speed +, -. and reset speed shortcuts

Attempted:

1. player.setPlaybackRate() via YouTube API (#ytlr-player__player-container-player)
2. video.playbackRate via HTMLMediaElement with a ratechange listener for play/pause
3. direct - player API + video.playbackRate
4. no-pitch-correction - some pipelines refuse a rate they can't pitch-correct; asking for raw resampling can be the difference
5. default-rate - webOS applies some media properties at pipeline (re)start, and defaultPlaybackRate is read then

The YTAF webview advertises VIDEO_SPEED, VIDEO_SPEED_NORMAL and PLAYBACK_RATE ("${rate}×"), and use_lava_variable_playback_rate set to true in the page config, and the settings menu is fully built and the feature flag is on.

webOS emulators/simulators decode video on a software decoder while real TV hardware decodes video on a hardware decoder, which is exactly why playback rate works on emu and not on TVs.

From some debugging, I came back with this data:

{
  "watchPage": true,
  "videoFound": true,
  "playerFound": true,
  "desiredSpeed": 1,
  "availableRates": [
    0.25,
    0.5,
    0.75,
    1,
    1.25,
    1.5,
    1.75,
    2
  ],
  "measured": {
    "default-rate": {
      "effective": 1.036,
      "property": 1.5,
      "works": false
    },
    "direct": {
      "effective": 1.009,
      "property": 1.5,
      "works": false
    },
    "no-pitch-correction": {
      "effective": 0.999,
      "property": 1.5,
      "works": false
    },
    "seek-nudge": {
      "effective": null,
      "property": 1.5,
      "works": false
    }
  },
  "paused": false,
  "playerMethods": [
    "setPlaybackRate",
    "getPlaybackRate",
    "getAvailablePlaybackRates"
  ],
  "playerRate": 1,
  "rateRelatedFlags": {
    "prefetch_coordinator_error_logging_sampling_rate": 1,
    "web_session_replay_sample_rate": 0.02,
    "ytidb_transaction_ended_event_rate_limit": 0.02
  },
  "readyState": 4,
  "src": "blob:https://www.youtube.com/3fa",
  "strategyIndex": 0,
  "strategyLocked": false,
  "totalFlags": 226,
  "videoRateBefore": 1
}

"works" false means that all attempts failed to change the playback rate. "seek-nudge" returned null, meaning that it wasn't tested in this pass, and might be possible. Playback rate would have to be set while the video is paused, so it wouldn't work while playing a video. I will test this strategy further.

[cremor]

I'm not sure if it's a good idea to spend time on this with the current app architecture. Speed adjustments work if the app is running as a Cobalt app (reference: webosbrew#6 (comment)). The base repository is currently working on a Cobalt version (see https://github.com/webosbrew/youtube-webos/milestone/14). If you plan to convert your app to a Cobalt app too, then this should "just work".