Webm supports multiple audio and subtitle tracks inside its RIFF container structure, why the hell arent browsers supporting it???

As discussed previously, browsers are quite complex and so adding a new feature (subtitles) is actually adding several features, on top of existing features (video player) that aren't really (arguably) core to the web experience.
(I think olds like me want to believe the web is still "for" text and static images, but the majority of users today are (allegedly) all-in on video.)
Anyway, what sub-features make up "simple" subtitles? Oh the usual: where are they sourced? What format? What language? What encoding? (Utf8 one can only pray) Left to right support? Asian character support? What font are you using? System fonts? Are they widely supported? Does any of it work on mobile? Who holds the relevant patents? Etc.
- I'll take complete video support over WebBluetooth, DRM, WebGL and other similar garbage.
  
  Why is webgl garbage? You don't think 3d online games should be able to exist?
  
  can we add webusb and direct filesystem access to the list?
- maybe the plugin system wasn't that bad of a concept for video players and such, but it should be more limited and especially secured in any way possible

Maybe considered in https://www.w3.org/2025/03/26-mse-text-tracks-minutes.html?
- Your username is purple. Thank you for developing the Voyager app lol
  
  I have a rule. Every time I come upon their posts in the wild or see a significant update, I donate.
  
  I’ve downloaded the app because of your comment!

Most sites use some custom js-based players instead of the native video tag anyways, so I don't exactly think it's an issue.
- Support for this feature would lessen the need for such players though, and anything that lessens the amount of JavaScript in the world is an objective moral good.
  
  Fair, although AFAIK we'd also need native hls support (outside safari) since it's quite commonly used as well. Although, that info might be outdated
  
  honestly, if it wasn't so piss easy to write, i wouldn't use it at all

Subtitles are not always simple text files in the source. They can come in various formats like SRT, WebVTT, Teletext, and VobSub—if they are present at all.
To integrate them into WebM, you must first determine if they exist, ensure they have the correct language tags (and tag them properly if they don’t), then extract them, convert them into a format compatible with the player, and finally remux them alongside the video and audio. This process can easily fail in an automated workflow if any of these conditions are unmet or if the subtitle format is incompatible.
Given this complexity, it’s understandable why many choose to avoid the effort rather than addressing whether WebM supports subtitles.
I am not defending anyone, but the process of it all makes it understandable, at least for me.

Maybe webm and mp4 files with multiple language tracks are usually played with a media player, not a web browser?
- pretty much every animation u see online nowerdays is a webm, i just think it would be nice if browsers would support the full feature set of it, it would allow to put captions over animations where the captions dont get compressed and hence would stay readable even at high compression
  
  One problem with that use case is that you as the creator doesn't control where (screen position) and how (font face, size, etc) the subtitles are rendered. The browser and user control that, so I doubt they would be widely used for meme because of this.
  However, I do agree that it would be nice to have support for it for other reasons.
  
  pretty much every animation u see online nowerdays is a webm
  false, I use websites with significant numbers of gif files for animation.
- I mean, modern web browsers are trying to be absolutely everything else as well. Fully supporting a format isn't exactly an outrageous expectation.
  
  I'm not suggesting that it's outrageous. Merely that it's probably not a high priority.
- YouTube supports multiple audio tracks and multiple language subtitles. Same for Netflix and pretty much all major streaming platforms.
  
  Sure, but most YouTube streams aren't delivered as a single webm or mp4 file, and the language & subtitle selection you're referring to aren't implemented by the browser (but instead by a JavaScript application downloaded from Google). So it's not what OP asked about.

Because Google wants subtitles hidden behind their server. There's your answer.

Because webbrowsers are webbrowsers and video players only on the side.

Unrelated to the question but I don't believe webm(matroska) is based on RIFF, webp is but that's separate.

You WANT to go back to the era of autoplay music on every fuckdamn page?
- Not sure what that has to do with "multiple audio and subtitle tracks". Would supporting that somehow lead to "autoplay music" any more than from the features that browsers already support?
- Only if it's midi and just one instrument.
  
  Midi you say? https://onlinesequencer.net/3571035
- yes

Because you touch yourself at night

I can't think of an occasion where I've been listening to something online and wanted tracks - everything that would benefit from having them, I would prefer to download and run via VLC anyways. I think there just isn't any demand for the switch, and it would break a lot of legacy tools (like auto-transcription bots) to switch, much as .webp has.