I don't think we want to show the cast button for media that uses unsupported codecs and we won't get the codec info until the media is preloaded.

We could in theory start preload if we detect user has a Chromecast, but I would not want wasting user's battery by doing a Chromecast search if preload is none / DataSaver is on.

Maybe we could do some best effort approach, e.g. if we know there's a Chromecast due to other reasons in Chrome (e.g. some site is using Presentation API or we know this client used Chromecast in the past).

The worse alternative would be to show the cast button for any media that's not preloaded and then notify the user it's not supported when the codecs are not compatible on casting.

Thoughts are welcome :)

Wouldn't the impact of checking for a Chrome Cast when preload=none vs preload=metadata/auto very low. I mean, the user will most likely have encountered other media with other preload values. In the case where we force preload none, that means that we would only check for Chrome Cast visibility when playback starts in which case, maybe that makes sense.

I realise my initial message was lacking a use case. The reason why it might be interesting to have is for the case where a webpage wants to have a <video> to play locally and a hidden <video> to use for remote playback. Given that the videos might be different, the website would have good reasons to not preload the hidden video.

We do need to preload the video's metadata to be able to detect if it's compatible.

Maybe we could treat availability callbacks presence to trigger preload ignoring DataSaver/preload=none if on not on mobile network? (note atm there will always be callbacks set by the controls / overlay cast button)

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Looking into impact.