Having trouble getting transparent backgrounds in ChatGPT images

I don’t have video/MP4 samples to share. My testing here was only for still-image transparency.

For video, transparency depends on the codec/container workflow supporting an alpha channel, so I wouldn’t assume ordinary MP4 output has the same behavior.

Relevant docs/context that you can check:

https://developer.apple.com/documentation/avfoundation/using-hevc-video-with-alpha

https://developer.chrome.com/blog/alpha-transparency-in-chrome-video

MDN Web Docs

Web video codec guide - Media | MDN

This guide introduces the video codecs you're most likely to encounter or consider using on the web, summaries of their capabilities and any compatibility and utility concerns, and advice to help you choose the right codec for your project's video.