Safari iPadOS 18.3.2 freezes when looping video elements

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Level 1

4 points

Bug Summary:

Safari freezes on iPad Pro 13" M4 (iPadOS 18.3.2) when looping <video> elements play through once.

Steps to Reproduce:

Open any website with an autoplay looping <video> element
Scroll to looping video
After one playthrough, Safari and iPadOS become unresponsive
Lock/unlock is required to recover, unless experimental flags are disabled (see below) in addition to Prevent Cross-Site Tracking being disabled

Tested Workarounds:

Disabling all 5 of the following plus Prevent Cross-Site Tracking resolves full lockup, but still causes a UI freeze (several seconds) which then resolves itself:

Disabling only some does not prevent freezing (have not tested every possible combination - only individual and all on/all off)
Disabling ITP ("Prevent Cross-Site Tracking") alone does not solve it unless combined with all 5 flags being off
Issue is new as of iPadOS 18.3.2 update, M4 13" iPad pro

Tested with safari cache/history cleared

Default settings on all other WebKit Feature Flags

All extensions disabled

Force close safari and re-open + page refresh for each setting configuration tested

iPad Pro, iPadOS 18

Posted on Apr 24, 2025 01:04 PM

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Answer 1

Level 1

4 points

Update:

This bug still occurs after update to iOS 18.4.1
some of the webkit feature flags above are retired in 18.4.1 and some new ones added
tested with new flags MediaSource prefers DecompressionSession and MediaSource automatically falls back to DecompressionSession set to ON (default OFF) and the freezing behavior still occurs

If user is ACTIVELY SCROLLING at the moment the video loops, the freeze does not occur. I tested this by scrolling up and down a short distance such that the video element remains on-screen at all times. It continuously plays.
If user's finger is on the screen but not actively moving to scroll, the freeze does still occur at the video loop transition point.
User input that occurs while the UI is visually frozen appears to work - if the user taps a link while the UI is frozen, when it recovers seconds later the browser will be on the new page that was linked; if the UI freeze occurs and the user scrolls while it is already frozen, upon recovery then the page will be in a new position consistent with the scrolling direction.
Settings --> Accessibility --> Reduce Motion ON does not resolve the issue either.

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