Reference player: liveDelay property ignored due to race condition

[spoeschel]

Environment

• The MPD passes the DASH-IF Conformance Tool on https://conformance.dashif.org/
• The stream has correct Access-Control-Allow-Origin headers (CORS)
• There are no network errors such as 404s in the browser console when trying to play the stream
• The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ
• The issue occurs in the latest reference client on http://reference.dashif.org/dash.js/ and not just on my page [vanilla repo version used]

• Link to playable MPD file: e.g. https://livesim.dashif.org/livesim/testpic_2s/Manifest.mpd
• Dash.js version: 3.1.2 nightly
• Browser name/version: Firefox 77.0.1
• OS name/version: Ubuntu MATE 18.04

Steps to reproduce

1. Use different values for the streaming.liveDelay property (e.g 10 and 30).
2. Play the stream and observe the displayed Live Latency.

Observed behaviour

The latency should be near the set value - however, the property has no visible impact.

Analysis

Due to a race condition, the default live delay (= null) is used:

The config is updated asynchronously, as soon as the config JSON has been downloaded by:

dash.js/samples/dash-if-reference-player/app/main.js

Line 242 in f29346d

$scope.player.updateSettings(config);

However, only a few lines later in the same function, the config is retrieved from the player and the values of a few properties processed:

dash.js/samples/dash-if-reference-player/app/main.js

Line 320 in f29346d

var currentConfig = $scope.player.getSettings();

So if the asynchronous config init takes place after this retrieval (which is case on my system), it will return the default values for the properties used here - instead of the values of the actual config JSON.

These properties may be updated upon certain conditions (or not). At least they are written back to the player when a stream is started:

dash.js/samples/dash-if-reference-player/app/main.js

Line 606 in f29346d

$scope.player.updateSettings(config);

I have only checked the liveDelay property, but as other properties are processed here as well, they may be affected, too.

Edit: fixed MPD to live stream

[dsilhavy]

Thanks, fixed in #3301

[spoeschel]

Thank you; this fixes the issue for me.

I'm not sure whether this could also affect the autoplay feature (which I don't use), as doLoad (where the affected variables are read) could in theory be invoked before the variables have been set. When I just tried with different delay values, it didn't occur on my machine, though (however BrowserSync visibly slows down the page reload).

Example URL: index.html?url=https://livesim.dashif.org/livesim/testpic_2s/Manifest.mpd&autoplay=true

dash.js/samples/dash-if-reference-player/app/main.js

Line 999 in d2c6b78

$scope.doLoad();