[Webkit-unassigned] [Bug 232076] New: Safari on iOS cannot play a video from data uri

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=232076

            Bug ID: 232076
           Summary: Safari on iOS cannot play a video from data uri
           Product: WebKit
           Version: Other
          Hardware: iPhone / iPad
                OS: Other
            Status: NEW
          Severity: Major
          Priority: P2
         Component: Media
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mail2lf at gmail.com

We have noticed a strange behaviour of Safari since iOS 15 update: whenever a webpage contains a <video /> element with src attribute set to a Data URI containing a video file, the playback either doesn't start at all or starts with very noticeable lags and stutters further.

Inspecting what's going on via Safari Dev Tools shows that the browser attempts to execute Accept: range queries against a Data URI, loading the whole file every time. This leads to terrible memory consumption (200-300Mb for 2Mb video) and seems to be preventing the playback from functioning properly. 

We tried different workarounds for the issue (referencing a Blob with video data instead of Data URI, dynamically swapping the src attribute etc etc) but nothing seems to help.

In short, it seems we now are unable to play a video on a webpage if it's embedded into HTML on iOS 15+ devices.

A few observations that might be useful:
1. <img /> tag with src attribute set to base64 video plays the file properly, does not issue repetitive requests
2. iOS devices prior to 15.0 do work just fine
3. File size seems to be irrelevant to issue (smaller files, however, have better chances of fitting into memory thus work more often, but still very unreliable).
4. iOS simulator demonstrates the same behaviour (and iOS 14 simulators work just fine, iOS 15 exhibit the issue)

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