I understand the first slide may not autoplay but this is in middle of deck. I have searched and most results are RevealJs rather than Quarto and suggest a different format.

but on page the video is not autoplaying. Add muted after autoplay to let your video file start playing automatically (but muted). However, muted autoplay is always allowed. Note: Chromium browsers do not allow autoplay in most cases. When present, the video will automatically start playing. It will also come with some mild performance improvements. and I have set YAML option for global autoplay: format: revealjs: auto-play-media: true. Definition and Usage The autoplay attribute is a boolean attribute. Notably, Chrome still isn't asking user permission before the video plays - the solution many on the web have been asking for - but the loading and playback will be a little bit smarter and less intrusive. Under the new setup, that video won't play until you click back to the relevant tab. The browser will still load the video as soon as the tab is opened, but it won't start it until you visit the page itself, hopefully preventing the usual surprise when a late-loading video starts up in the background. A new post from engineer François Beaufort laid out Chrome's new approach, which will block playback as long as a given autoplay video is in a background tab. Chrome is getting more aggressive about that least popular web feature: autoplay video.

Chrome autoplay video stack overflow