Transparency in video

Description

Currently, to use video or an animated image with transparency, developers are stuck either using older formats like WebP, or exporting multiple formats (both HEVC and VP9).

Full interoperability between browsers would mean all browsers reliably supporting:

• transparency for HEVC
• transparency for VP9 WebM (Safari does not support transparency)
• animated JPEG-XL (JPEG-XL supports transparency, but animation is not supported in Safari)
• animated AVIF (all browsers support animated AVIF but it is bug-ridden in Safari when opacity is used)

There’s overlap in the use cases for the functionality above, so the following would suffice (because JPEG-XL probably isn't a great option for animation):

• transparency for VP9
• fix bugs affecting animated AVIF when transparency is used

There is a pull request for adding transparency for VP9 to Safari.

See also following blog post: Video with alpha transparency on the web

Rationale

The current situation is frustrating: see, for example, the Reddit post Can we talk about the pain of transparent video browser support in 2025 which has 70 upvotes.

Investigation Roadmap

No response

Start by reviewing the linked WebKit pull request and the Safari issues for VP9 transparency and animated AVIF opacity. Compare the browser-support gaps described in the issue with the referenced blog post; done means the requested transparency and animated-AVIF behavior work reliably across browsers.