Bug 260468 – XSLT can take minutes to render with many <audio> elements

• Status: RESOLVED
• Resolution: MOVED
• Component: Media

[Jonathan del Strother]

I'd like to use XSLT to transform RSS feeds into user-viewable pages.

When Safari renders lots of <audio> elements via XSLT, it behaves terribly - seemingly getting exponentially slower as the number of <audio> elements increases.

On a sample feed with 515 episodes, Safari 16.5.2 appears to freeze while loading the page for around 52 seconds on my M1 Macbook Pro. Meanwhile a 2016 MBP takes 3 minutes 10 seconds…

Firefox & Chrome both render the same page more-or-less instantly.

Here’s the sample page with 515 episodes: https://d1k0jgp8xx8zuc.cloudfront.net/jds/xsl/fish.rss
But for the sake of everyone’s sanity if you don’t want to sit there waiting for it to load, here’s a version with 100 episodes: https://d1k0jgp8xx8zuc.cloudfront.net/jds/xsl/fish-truncated.rss .  It ‘only’ takes 5 seconds to render, but hopefully that’s enough to demonstrate the problem.


(I've also filed this via Feedback Assistant, if that helps: FB12904190)

[Alexey Proskuryakov]

It is a known issue that rendering a page with many media elements is pathologically slow, but I cannot find the tracking bug now.

Doing an outrageous amount of work under HTMLMediaElement::ensureMediaControls() -> HTMLMediaElement::setupAndCallJS() -> ... jsCSSStyleDeclaration_propertyValueForCamelCasedIDLAttribute() ... Document::updateStyleIfNeeded().

[Radar WebKit Bug Importer]

<rdar://problem/114278433>

[Alexey Proskuryakov]

rdar://113627244

[Simon Fraser (smfr)]

This is covered by <rdar://77347577>.

[Jonathan del Strother]

Could you let us know the status of rdar://77347577 ?