Hi Jean-Yves,

Thanks for the quick and detailed response, and for the helpful links.

> Are you referring to audible video elements requiring a user gesture for playback to start?

To clarify, I’m aware of the standard autoplay policies and user gesture requirements for unmuted playback, and I agree that those are well-documented and expected.

What I’m describing appears to be a distinct issue - not about autoplay initiation, but about ongoing playback being unexpectedly paused by the browser after it has already started, particularly when multiple unmuted <video> elements are playing concurrently. This happens even after a proper user gesture and successful play() call.

> I’m not aware of any such restrictions.

After capturing logs and digging into the WebKit source code, I found that the restriction I’m referring to is implemented as follows::
1. The `ConcurrentPlaybackNotPermitted` policy is enforced only on iOS, which explains why there’s no issue on macOS (I haven’t tested on iPad). Source code: https://github.com/WebKit/WebKit/blob/45d0c14d08a78058a88d16460f1fbc10946634c0/Source/WebCore/platform/audio/ios/MediaSessionManagerIOS.mm#L85
2. The logic that iterates over all media elements and enforces pause is here: https://github.com/WebKit/WebKit/blob/main/Source/WebCore/platform/audio/PlatformMediaSessionManager.cpp#L292-L300
3. The implementation of the "can play concurrently" check, which effectively disallows concurrent playback of audible media unless the source is a MediaStream, is here: https://github.com/WebKit/WebKit/blob/45d0c14d08a78058a88d16460f1fbc10946634c0/Source/WebCore/platform/audio/PlatformMediaSession.cpp#L377-L390
4. There are also tests that explicitly verify that calling play() on one video element pauses all others:
    a) https://github.com/WebKit/WebKit/blob/main/LayoutTests/media/video-concurrent-playback-expected.txt;
    b) https://github.com/WebKit/WebKit/blob/main/LayoutTests/media/video-multiple-concurrent-playback-expected.txt.

To demonstrate the issue, I’ve created a test page:
https://mstyura.github.io/webkit-issues/audible-video-concurrent-playback/index.html

It contains 4 HLS video elements and two buttons: “Play All” and “Pause All.”
Clicking “Play All” results in only one video playing effectively. Repeating the action multiple times shows that behavior is non-deterministic.

There’s also a “workaround mode” that starts all videos muted. In that case, all 4 videos initially play—but later WebKit sometimes detects concurrent playback (during media element time updates from HTMLMediaElement::updatePlayState https://github.com/WebKit/WebKit/blob/156848f5d55261b92551457dec064ff946ca45b9/Source/WebCore/html/HTMLMediaElement.cpp#L6398) and starts pausing them again.
This leads to the observed ping-pong effect between JavaScript and WebKit.

Demo source: https://github.com/mstyura/WebKit-Issues/blob/main/audible-video-concurrent-playback/index.html

My question is:
Is this behavior still considered desirable in 2025, especially given that developers can bypass it with more complex (but less power-efficient) workarounds like WebCodecs + <canvas> or/and VideoTrackGenerator + AudioContext.createMediaStreamDestination()?

Thanks again for your time and insights!

On Wed, Apr 30, 2025 at 2:28 PM Jean-Yves Avenard <jean-yves.avenard@apple.com> wrote:


On 30 Apr 2025, at 9:57 pm, Yury Yarashevich via webkit-dev <webkit-dev@lists.webkit.org> wrote:

Hi WebKit team,

I’m curious about the original rationale behind the restriction that prevents concurrent playback of multiple <video> elements. Was it primarily introduced to save battery life?


I’m not aware of any such restrictions.

Here is a test page that will literally let you play hundreds of video elements at the same time.

It works on any Apple devices: iPhone, iPad, Vision Pro, Mac .

In practice, this behavior appears to have unintended side effects. There’s a reproducible issue where playback can be started with the video muted and then immediately unmuted, effectively bypassing the restriction. However, this often results in videos being randomly paused later—sometimes very frequently—leading to a “play/pause ping-pong” between Safari/WebKit and JavaScript restarting playback. This erratic behavior may actually increase battery consumption, despite appearing to work smoothly from the user’s perspective.

Are you referring to audible video elements requiring a user gesture for playback to start?

This behaviour isn’t erratic and is well defined and and up to know I thought it was well understood. For an audible element to play, the user needs to first interact with the video element such as clicking on the video or its controls.
This behaviour is even defined through HTML5 specifications including how you can detect if the User Agent will allow video to start autoplaying without a user gesture.

Similar policies are implemented by other user agents such as Firefox and Chrome.
There’s an article on MDN on how to deal with them

Here is a more WebKit-focus article


Here is a similar article written by the Chrome team on the same topic

Here is the HTML5 specifications related to this matter


Even if this workaround is eventually blocked, developers who rely on concurrent playback (e.g., outside of WebRTC contexts) will turn to more complex solutions, such as decoding video and audio using WebCodecs or/and WebAssembly, and rendering via <canvas> and AudioContext. While technically feasible, these approaches are likely to be significantly less power-efficient than simply allowing multiple <video> elements to play concurrently.
Another similarly inefficient workaround would be to synthesize a MediaStream using the VideoTrackGenerator API and AudioContext.createMediaStreamDestination().

Lastly, another issue is that creating a MediaElementSource from a <video> element and routing its audio through a shared AudioContext also does not disable the playback restriction—whereas it is disabled when the <video> element itself is muted. This feels inconsistent and may point to a separate bug.

Could you please clarify the motivation behind this restriction, and whether there are any plans to revisit or improve its behavior?


I believe I answered this question above, and through the various links provided.


Cheers
JY