webOS 4 | UI stalls during playback

[TomaszKowalik]

Hi,

We’re observing a reproducible UI responsiveness issue on webOS 4 devices during video playback using RxPlayer (and also Shaka Player).

During playback, the device experiences regular UI stalls / freezes:

• UI becomes non-responsive for ~1–1.5 seconds
• then recovers briefly
• repeats continuously while playback is active
• issue also occurs when video is paused (so not tied to decoding only)

This creates a noticeable “laggy UI” experience during playback sessions. Playback is running fine tho.

I added a simple main-thread stall detector:

let last = performance.now();

setInterval(function () {
    const now = performance.now();

    if (now - last > 200) {
        console.log("STALL", now - last);
    }

    last = now;
}, 50);

~1300+ “STALL” events are observed during a playback session. Pattern is consistent and continuous while media is loaded/playing.
This suggests main thread long tasks or scheduling delays, not random spikes. Likely main thread blocking caused by MSE + JS playback loop overhead. Native webOS player (non-MSE) does not show this issue.

At this point we’re unsure whether this is a device limitation, and webOS 4 CPU / browser engine cannot handle MSE playback load without UI blocking, or perhaps there are RxPlayer configuration optimizations that could significantly reduce that lagging ?

[jilles-sg]

@TomaszKowalik RxPlayer's multi-threading mode documented at https://github.com/canalplus/rx-player/blob/243a5e6bcfdea7dbf49ab753493c2d276016bdbb/doc/Getting_Started/MultiThreading.md might help, although the slowest devices also tend to have the oldest Web engines that lack useful features like workers.

[Florent-Bouisset]

Hello @TomaszKowalik,
As @jilles-sg suggested, you can try enabling multi-threading mode and see whether it improves performance.
On devices that supports it, MSE APIs can be accessed from within a web worker which can bring additional improvements, this is what we called "MSE in worker".
However, on the device you mentioned it's possible that MSE in worker is not supported.

But if the device supports web worker you may still see some benefit for using it with the rx-player, because logic such as segment requests, ABR calculation will be run on a separate thread. From our experience we have seen significative improvement when using this on lower-end devices.