[Webkit-unassigned] [Bug 198583] New: MediaSource.isTypeSupported claims FLAC-in-MP4 support on iOS and macOS, but plays silence

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=198583

            Bug ID: 198583
           Summary: MediaSource.isTypeSupported claims FLAC-in-MP4 support
                    on iOS and macOS, but plays silence
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Macintosh
                OS: macOS 10.14
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Media
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: bvibber at wikimedia.org

MediaSource.isTypeSupported('audio/mp4; codecs="flac"') returns true in Safari 12.1.1 and Tech Preview on macOS 10.14, and iOS 12.4 & iPadOS 13 beta, however this doesn't appear to be supported in my testing, with FLAC-in-MP4 files produced by ffmpeg or manually synthesized.

Example page with short h.264-in-fMP4 and FLAC-in-fMP4 tracks that plays no audio in Safari:
https://brionv.com/misc/msetest4/flac.html

Expected behavior:
Either an exception should be thrown when creating the buffer due to unsupported codec, or it should work.

Actual behavior:
Acts as though audio is valid and present but only silence is heard.

Behavior is the same in both macOS and iOS: no audio, no error.


Note that a _bare_ FLAC stream with 'audio/flac' type works with MSE on macOS and correctly returns false for isMediaType / throws an exception on buffer creation on iOS 13 beta, where I guess no FLAC support is present in the system. Variant example showing correct expected behavior for the different container: https://brionv.com/misc/msetest4/flac2.html

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