1950502 - AudioContext#createMediaElementSource breaks playback of DRM (EME) content

Status: UNCONFIRMED

(Core :: Web Audio, defect, P3)

Description

[Ian]

User Agent: "Mozilla/5.0 (X11; Linux x86_64; rv:135.0) Gecko/20100101 Firefox/135.0"
Build ID: 20181001000000

Steps to reproduce:

• Take an EME-enabled audio tag (fmp4+flac, any CDM like widevine)
• Call AudioContext#createMediaElementSource(audio)
• No sound/playback

Actual results:

When calling createMediaElementSource on a DRM-protected audio element (using EME), Firefox silently breaks playback. This results in no sound output and no progress of the media file, preventing the use of additional audio processing nodes like GainNode.

Expected results:

Similar to Chrome, calling createMediaElementSource on a DRM-protected audio element should return a valid MediaElementSourceAudioNode instance, allowing for further manipulation using Web Audio API features and correct playback.

Comment 1

[Ian]

We have successfully reproduced this issue on both Linux and macOS operating systems. So if you need a test demo to reproduce the issue, I can provide a GitHub repository with sample files and demo code. Please let me know if this would be useful.

Comment 2

[Karl Tomlinson (:karlt)]

Media data processed by a CDM MAY be unavailable through web platform APIs in the usual way (for example using the CanvasRenderingContext2D drawImage() method and the AudioContext MediaElementAudioSourceNode). This specification does not define conditions for such non-availability of media data, however, if media data is not available to through such APIs then they MAY behave as if no media data was present at all.

I'm not sure what exactly would be meant by "no media data was present at all", but even if providing silence, I would have expected currentTime to advance on the media element and the usual events to be dispatched.

The HTMLMediaElement MUST behave in an identical fashion after the MediaElementAudioSourceNode has been created, except that the rendered audio will no longer be heard directly, but instead will be heard as a consequence of the MediaElementAudioSourceNode being connected through the routing graph. Thus pausing, seeking, volume, src attribute changes, and other aspects of the HTMLMediaElement MUST behave as they normally would if not used with a MediaElementAudioSourceNode..

Comment 3

[Karl Tomlinson (:karlt)]

Changes for Bug 1331763 intended to provide the so-called DRM-protected audio in an unprotected manner to Web Audio in Firefox 55, but the test merely checked that createMediaElementSource() does not throw.

It would be good to know whether any previous versions of Firefox would unprotect the audio as intended.

https://mozilla.github.io/mozregression/ can be helpful with that and can help identify when and why the behavior changed, if it has.