1409664 - Implement supports for MediaCapabilities object

Status: RESOLVED FIXED

(Core :: Audio/Video: Playback, enhancement, P2)

Description

[Jean-Yves Avenard [:jya]]

This bug is to track support for Media Capabilities as proposed by Google.

Do we want to support this object, do we have fingerprinting concerns and so on.

Comment 1

[Blake Wu [:bwu][:blakewu]]

Ethan,
Are there any concerns from the security perspective, like anti-fingerprinting?

Comment 2

[Ethan Tseng [:ethan]]

In the abstract of the spec [1]:
"The APIs will expose information about the decoding and encoding capabilities for a given format but also output capabilities to find the best match based on the device’s display."

I imagine this will be a fingerprinting attribute, similar to the MediaDevices API [2], which we are adding fingerprinting protection in bug 1372073.

Since this is a new API, we should let the Tor Browser be aware of it.
Once we confirmed it's a fingerprinting threat, we will file a new bug for the protection work.


[1] https://wicg.github.io/media-capabilities/
[2] https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices

Comment 3

[Tom Ritter [:tjr] (OOTO until 4/30 at least)]

I opened https://github.com/WICG/media-capabilities/issues/48

Comment 4

[John Lin [:jhlin][:jolin]]

IMHO, now that media decoding/encoding stack for playback and WebRTC will be unified (or is it already so?), we should also strive to have only one capability decision implementation for both if deciding to support this.

Comment 5

[Jean-Yves Avenard [:jya]]

This appears to be the most wanted feature by all the partners we've met...

Comment 6

[Phabricator Automation]

Attachment: Bug 1409664 - P1. Add MediaCapabilities skeleton IDL.

As per https://wicg.github.io/media-capabilities/#idl-index

Placed behind user pref media.mediacapabilities.enabled that is disabled by default

MozReview-Commit-ID: 9zg4aRdGolw

Comment 7

[Phabricator Automation]

Attachment: Bug 1409664 - P2. Add ScreenLuminance objects and friends to Screen

As per https://wicg.github.io/media-capabilities/#idl-index

MozReview-Commit-ID: 1W7DAfYb7ut

Depends on D1613

Comment 8

[Phabricator Automation]

Attachment: Bug 1409664 - P3. Allow audio/webm container type in MediaRecorder.

MozReview-Commit-ID: 5qq2VxSM58z

Depends on D1614

Comment 9

[Phabricator Automation]

Attachment: Bug 1409664 - P4. Provide basic MediaCapabilities support

The information returned is identical to
1- canPlayType() for file
2- MediaSource.isTypeSupported for media-source
3- MediaRecorder.isTypeRecorder() for recordings.

MozReview-Commit-ID: 2JeGx9o8ozv

Depends on D1616

Comment 10

[Phabricator Automation]

Attachment: Bug 1409664 - P5. Fix comment

MozReview-Commit-ID: 4FaLAZl7Ca3

Depends on D1617

Comment 11

[Phabricator Automation]

Attachment: Bug 1409664 - P6. Remove flac in ogg preference

Let's always enable it.

MozReview-Commit-ID: 1cwI8LHRynu

Depends on D1618

Comment 12

[Phabricator Automation]

Attachment: Bug 1409664 - P7. Remove unused TaskQueue method

MozReview-Commit-ID: HlGQjUtocvU

Depends on D1619

Comment 13

[Phabricator Automation]

Attachment: Bug 1409664 - P8. Make explicit shutdown of TaskQueue optional

Can be used in place of a TaskQueue, but without the need to explicitly shut it down. It will automatically be shutdown once it's no longer referenced.

MozReview-Commit-ID: 1lJcTqtk2r6

Depends on D1620

Comment 14

[Phabricator Automation]

Attachment: Bug 1409664 - P9. Remove AutoTaskQueue and its use

It is used outside MSE, ultimately this should move to xpcom inside TaskQueue.h

MozReview-Commit-ID: GpoGnhVA0X5

Depends on D1621

Comment 15

[Phabricator Automation]

Attachment: Bug 1409664 - P10. Extend MediaExtendedMIMEType to know about audio configuration

Addtionally, change the framerate to be of type double and allow to create a MediaExtendedMIMEType based on the new dom VideoConfiguration and AudioConfiguration object.

MozReview-Commit-ID: B1VkOhmzsdU

Depends on D1622

Comment 16

[Phabricator Automation]

Attachment: Bug 1409664 - P11. Add GetTracksInfo method to all MediaDecoder instances

Allows to build an array ot TrackInfo built from the mimetype provided. This will allow to create dummy decoder to check that if they are supported and how well the decoder will perform.

MozReview-Commit-ID: I4OH9EY1Ldl

Depends on D1623

Comment 17

[Phabricator Automation]

Attachment: Bug 1409664 - P12. Don't attempt to play non-supported AAC sampling rate

We know those sampling rate aren't supported and cause initialization errors later.

MozReview-Commit-ID: Ds1yLd0h6rI

Depends on D1624

Comment 18

[Phabricator Automation]

Attachment: Bug 1409664 - P13. Report the Apple's H264 decoder is hardware accelerated when not yet initialized

We can't create a H264 VT decoder until we have all SPS/PPS NALs, which makes it tricky to generate when we only want to check if H264 is supported.
On mac, we can reasonable assume that hardware acceleration is always supported (though on a mac pro 2013 that isn't the case or hackintosh with nvidia cards).

MozReview-Commit-ID: nS2VVLYN39

Depends on D1625

Comment 19

[Phabricator Automation]

Attachment: Bug 1409664 - P14. Provide more details for audio and video configuration

We now provides more detailed information for audio (check sampling rate and channels if provided).

And check for the power efficient attribute. We directly correlate this information with the decoder being hardware accelerated or not. All audio codecs are deemed to be power efficient.

MozReview-Commit-ID: HcZlbMDSADb

Depends on D1626

Comment 20

[Phabricator Automation]

Attachment: Bug 1409664 - P15. Update wpt expected results

Most tests will pass now.
The remaining tests failing are related to incompatibility with our bindings generator, and will be addressed in a later change.

MozReview-Commit-ID: HGrJ5gT9aHd

Depends on D1627

Comment 21

[Phabricator Automation]

Attachment: Bug 1409664 - P16. Fix canPlayType so that it checks codecs if provided

For flac, mp3 and adts, if a codec was provided but wasn't supported in the container, it would have reported Maybe instead of No

MozReview-Commit-ID: ECMNX1R8hTz

Depends on D1628

Comment 22

[Phabricator Automation]

Attachment: Bug 1409664 - P17. Fix typo in variable name

MozReview-Commit-ID: 1Yamljittrh

Depends on D1629

Comment 23

[Phabricator Automation]

Attachment: Bug 1409664 - P18. Remove unused variables

Silence warnings.

Depends on D1630

MozReview-Commit-ID: GTzH2UtEBXz

Comment 24

[Phabricator Automation]

Attachment: Bug 1409664 - P19. Properly pass KnowsCompositor object to decoder

To properly determine if a decoder is hardware accelerated, we must pass information about the compositor to the decoder.

MozReview-Commit-ID: J9AkfbIBIM0

Depends on D1631

Comment 25

[Phabricator Automation]

Attachment: Bug 1409664 - P20. Don't wrap H264 decoder in H264 converter

By default, when creating a H264 decoder it is wrapped into a H264Converter which will only create the actual decoder once a valid SPS/PPS has been seen.
As creating valid SPS/PPS NALs isn't trivial, when all we care about are capabilities of such decoder, we do not wrap the decoder so that it will be immediately created.
We can then test its capabilities.

We only enable this on windows, as on mac we need to generate a SPS/PPS, otherwise the mac decoder always report that HW decoding is not enabled.

Depends on D1632
MozReview-Commit-ID: Iir5yvFRyYr

Comment 26

[Phabricator Automation]

Comment on attachment 8984981 [details]
Bug 1409664 - P12. Don't attempt to play non-supported AAC sampling rate

Paul Adenot (:padenot) has approved the revision.

https://phabricator.services.mozilla.com/D1625

Comment 27

[Phabricator Automation]

Comment on attachment 8984970 [details]
Bug 1409664 - P3. Allow audio/webm container type in MediaRecorder.

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1616

Comment 28

[Phabricator Automation]

Attachment: Bug 1409664 - P21. Add BitWriter class

MozReview-Commit-ID: lTBhFzO38l

Comment 29

[Phabricator Automation]

Comment on attachment 8984971 [details]
Bug 1409664 - P4. Provide basic MediaCapabilities support

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1617

Comment 30

[Phabricator Automation]

Comment on attachment 8984972 [details]
Bug 1409664 - P5. Fix comment

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1618

Comment 31

[Phabricator Automation]

Comment on attachment 8984973 [details]
Bug 1409664 - P6. Remove flac in ogg preference

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1619

Comment 32

[Phabricator Automation]

Comment on attachment 8984974 [details]
Bug 1409664 - P7. Remove unused TaskQueue method

Gerald Squelart [:gerald] has approved the revision.

https://phabricator.services.mozilla.com/D1620

Comment 33

[Phabricator Automation]

Comment on attachment 8985757 [details]
Bug 1409664 - P21. Add BitWriter class

Gerald Squelart [:gerald] has approved the revision.

https://phabricator.services.mozilla.com/D1678

Comment 34

[Phabricator Automation]

Attachment: Bug 1409664 - P22. Retrieve H264 constraint flags with ExtractH264CodecDetails

We'll need it to properly build a SPS/PPS extradata later. Also, change the types used. The original data is stored on two bytes ASCII, it will always fit in a uint8_t. Additionally, this is how those values are stored in a SPS.

MozReview-Commit-ID: C1UBU7OqhQM

Depends on D1678

Comment 35

[Phabricator Automation]

Attachment: Bug 1409664 - P23. Create SPS/PPS extradata to better determine decoder capabilities

The Apple VT decoder requires SPS+PPS at construction time. If not provided, in earlier macOS it used to give an error. In the current 10.13 it appears to work, however the decoder always report to be software only.

To properly determine the decoder capabilities, we construct a SPS NAL from the codec mimetype provided.

Details on the structure of the mimetype can be found in https://tools.ietf.org/html/rfc6381#section-3.3 and is a 1:1 match with the data found in the SPS.

MozReview-Commit-ID: I0WeTux14K4

Depends on D1718

Comment 36

[Phabricator Automation]

Comment on attachment 8984977 [details]
Bug 1409664 - P8. Make explicit shutdown of TaskQueue optional

Gerald Squelart [:gerald] has approved the revision.

https://phabricator.services.mozilla.com/D1621

Comment 37

[Phabricator Automation]

Comment on attachment 8984978 [details]
Bug 1409664 - P9. Remove AutoTaskQueue and its use

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1622

Comment 38

[Phabricator Automation]

Comment on attachment 8984979 [details]
Bug 1409664 - P10. Extend MediaExtendedMIMEType to know about audio configuration

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1623

Comment 39

[Phabricator Automation]

Comment on attachment 8984980 [details]
Bug 1409664 - P11. Add GetTracksInfo method to all MediaDecoder instances

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1624

Comment 40

[Phabricator Automation]

Comment on attachment 8984982 [details]
Bug 1409664 - P13. Report the Apple's H264 decoder is hardware accelerated when not yet initialized

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1626

Comment 41

[Phabricator Automation]

Comment on attachment 8984983 [details]
Bug 1409664 - P14. Provide more details for audio and video configuration

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1627

Comment 42

[Phabricator Automation]

Comment on attachment 8984984 [details]
Bug 1409664 - P15. Update wpt expected results

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1628

Comment 43

[Phabricator Automation]

Comment on attachment 8984985 [details]
Bug 1409664 - P16. Fix canPlayType so that it checks codecs if provided

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1629

Comment 44

[Phabricator Automation]

Comment on attachment 8984987 [details]
Bug 1409664 - P17. Fix typo in variable name

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1630

Comment 45

[Phabricator Automation]

Comment on attachment 8984988 [details]
Bug 1409664 - P18. Remove unused variables

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1631

Comment 46

[Phabricator Automation]

Comment on attachment 8984990 [details]
Bug 1409664 - P19. Properly pass KnowsCompositor object to decoder

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1632

Comment 47

[Phabricator Automation]

Comment on attachment 8984991 [details]
Bug 1409664 - P20. Don't wrap H264 decoder in H264 converter

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1633

Comment 48

[Phabricator Automation]

Comment on attachment 8986332 [details]
Bug 1409664 - P22. Retrieve H264 constraint flags with ExtractH264CodecDetails

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1718

Comment 49

[Phabricator Automation]

Comment on attachment 8986333 [details]
Bug 1409664 - P23. Create SPS/PPS extradata to better determine decoder capabilities

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1719

Comment 50

[Phabricator Automation]

Attachment: Bug 1409664 - P25. Don't use main thread with Benchmark . r?bryce

Instead have it use its own task queue.

Depends on D1767

Comment 51

[Phabricator Automation]

Attachment: Bug 1409664 - P26. Use VP9 benchmark results to determine smoothness. r?bryce

If the benchmark task hasn't run yet, we will assume smoothness for now.

Depends on D1771

Comment 52

[Phabricator Automation]

Attachment: Bug 1409664 - P24. Make IsVP9DecodeFast usable on any thread. r?bryce

This will allow to be called from the MediaCapabilities taskqueue if we find that a decoder won't be hardware accelerated.

It is still assumed that Benchmark::Init() was called at least once on the main thread.

Depends on D1628

Comment 53

[Phabricator Automation]

Comment on attachment 8987125 [details]
Bug 1409664 - P24. Make IsVP9DecodeFast usable on any thread. r?bryce

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1767

Comment 54

[Phabricator Automation]

Attachment: Bug 1409664 - P27. Don't disable webm container for MSE::isTypeSupported when MediaCapabilities is enabled. r?bryce

MediaCapabilities provide a finer detail on VP9 being supported or not. YouTube will use that information to determine which resolutions to support when using VP9

Depends on D1772

Comment 55

[Phabricator Automation]

Attachment: Bug 1409664 - P28. Extrapolate VP9 benchmark results for requested vp9 configuration. r?bryce

Additionally, consider all videos <= 480p to be smooth and power efficient as:
1- Hardware decoding it typically not used for those
2- We can't do any better
3- Any machines should be able to do 480p

Depends on D1794

Comment 56

[Phabricator Automation]

Comment on attachment 8987122 [details]
Bug 1409664 - P25. Don't use main thread with Benchmark . r?bryce

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1771

Comment 57

[Phabricator Automation]

Comment on attachment 8987123 [details]
Bug 1409664 - P26. Use VP9 benchmark results to determine smoothness. r?bryce

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1772

Comment 58

[Phabricator Automation]

Comment on attachment 8987376 [details]
Bug 1409664 - P27. Don't disable webm container for MSE::isTypeSupported when MediaCapabilities is enabled. r?bryce

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1794

Comment 59

[Phabricator Automation]

Comment on attachment 8987458 [details]
Bug 1409664 - P28. Extrapolate VP9 benchmark results for requested vp9 configuration. r?bryce

Bryce Van Dyk (:bryce) has approved the revision.

https://phabricator.services.mozilla.com/D1796

Comment 60

[Phabricator Automation]

Comment on attachment 8984990 [details]
Bug 1409664 - P19. Properly pass KnowsCompositor object to decoder

Boris Zbarsky [:bz] (no decent commit message means r-) has approved the revision.

https://phabricator.services.mozilla.com/D1632

Comment 61

[Phabricator Automation]

Comment on attachment 8984968 [details]
Bug 1409664 - P1. Add MediaCapabilities skeleton IDL.

Boris Zbarsky [:bz] (no decent commit message means r-) has approved the revision.

https://phabricator.services.mozilla.com/D1613

Comment 62

[Phabricator Automation]

Comment on attachment 8984969 [details]
Bug 1409664 - P2. Add ScreenLuminance objects and friends to Screen

Boris Zbarsky [:bz] (no decent commit message means r-) has approved the revision.

https://phabricator.services.mozilla.com/D1614

Comment 63

[Phabricator Automation]

Comment on attachment 8984983 [details]
Bug 1409664 - P14. Provide more details for audio and video configuration

Andrea Marchesini [:baku] has approved the revision.

https://phabricator.services.mozilla.com/D1627

Comment 64

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/56cfc9b388ed
P1. Add MediaCapabilities skeleton IDL. r=bz
https://hg.mozilla.org/integration/mozilla-inbound/rev/c27874c06658
P2. Add ScreenLuminance objects and friends to Screen. r=bz
https://hg.mozilla.org/integration/mozilla-inbound/rev/89d390fbbfc2
P3. Allow audio/webm container type in MediaRecorder. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/58be92b1a730
P4. Provide basic MediaCapabilities support. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/f465c541d485
P5. Fix comment. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/9c4f6e1376b8
P6. Remove flac in ogg preference. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/779fdf8781bd
P7. Remove unused TaskQueue method. r=gerald
https://hg.mozilla.org/integration/mozilla-inbound/rev/75ea1b10a437
P8. Make explicit shutdown of TaskQueue optional. r=gerald
https://hg.mozilla.org/integration/mozilla-inbound/rev/dcb3d64ed761
P9. Remove AutoTaskQueue and its use r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/c9ebc35c018f
P10. Extend MediaExtendedMIMEType to know about audio configuration. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/cc96ea98ea5f
P11. Add GetTracksInfo method to all MediaDecoder instances. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/ab4b6e060b8f
P12. Don't attempt to play non-supported AAC sampling rate. r=padenot
https://hg.mozilla.org/integration/mozilla-inbound/rev/6c6d943c1aa4
P13. Report the Apple's H264 decoder is hardware accelerated when not yet initialized. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/191b6cabf55b
P14. Provide more details for audio and video configuration. r=bryce, r=baku
https://hg.mozilla.org/integration/mozilla-inbound/rev/c98c9828c2dc
P15. Fix canPlayType so that it checks codecs if provided. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/82eccef03093
P16. Fix typo in variable name. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/db78b712d5ec
P17. Remove unused variables. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/25ff69daabca
P18. Properly pass KnowsCompositor object to decoder. r=bryce, r=bz
https://hg.mozilla.org/integration/mozilla-inbound/rev/6fe4e0609af6
P19. Don't wrap H264 decoder in H264 converter. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/b77050ae2d43
P20. Add BitWriter class. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/128bb8d855d4
P21. Retrieve H264 constraint flags with ExtractH264CodecDetails. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/95f7bce33797
P22. Create SPS/PPS extradata to better determine decoder capabilities. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/58e74a5ac2c2
P23. Update wpt expected results. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/14717f5f8f8f
P24. Make IsVP9DecodeFast usable on any thread. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/cd93530bc66e
P25. Don't use main thread with Benchmark . r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/b9081b427eae
P26. Use VP9 benchmark results to determine smoothness. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/d3c49681033c
P27. Don't disable webm container for MSE::isTypeSupported when MediaCapabilities is enabled. r=bryce
https://hg.mozilla.org/integration/mozilla-inbound/rev/994fa896ebaf
P28. Extrapolate VP9 benchmark results for requested vp9 configuration. r=bryce

Comment 65

[Stefan Hindli [:stefan_hindli]]

https://hg.mozilla.org/mozilla-central/rev/56cfc9b388ed
https://hg.mozilla.org/mozilla-central/rev/c27874c06658
https://hg.mozilla.org/mozilla-central/rev/89d390fbbfc2
https://hg.mozilla.org/mozilla-central/rev/58be92b1a730
https://hg.mozilla.org/mozilla-central/rev/f465c541d485
https://hg.mozilla.org/mozilla-central/rev/9c4f6e1376b8
https://hg.mozilla.org/mozilla-central/rev/779fdf8781bd
https://hg.mozilla.org/mozilla-central/rev/75ea1b10a437
https://hg.mozilla.org/mozilla-central/rev/dcb3d64ed761
https://hg.mozilla.org/mozilla-central/rev/c9ebc35c018f
https://hg.mozilla.org/mozilla-central/rev/cc96ea98ea5f
https://hg.mozilla.org/mozilla-central/rev/ab4b6e060b8f
https://hg.mozilla.org/mozilla-central/rev/6c6d943c1aa4
https://hg.mozilla.org/mozilla-central/rev/191b6cabf55b
https://hg.mozilla.org/mozilla-central/rev/c98c9828c2dc
https://hg.mozilla.org/mozilla-central/rev/82eccef03093
https://hg.mozilla.org/mozilla-central/rev/db78b712d5ec
https://hg.mozilla.org/mozilla-central/rev/25ff69daabca
https://hg.mozilla.org/mozilla-central/rev/6fe4e0609af6
https://hg.mozilla.org/mozilla-central/rev/b77050ae2d43
https://hg.mozilla.org/mozilla-central/rev/128bb8d855d4
https://hg.mozilla.org/mozilla-central/rev/95f7bce33797
https://hg.mozilla.org/mozilla-central/rev/58e74a5ac2c2
https://hg.mozilla.org/mozilla-central/rev/14717f5f8f8f
https://hg.mozilla.org/mozilla-central/rev/cd93530bc66e
https://hg.mozilla.org/mozilla-central/rev/b9081b427eae
https://hg.mozilla.org/mozilla-central/rev/d3c49681033c
https://hg.mozilla.org/mozilla-central/rev/994fa896ebaf

Comment 66

[Georg Koppen]

(In reply to Ethan Tseng [:ethan] from comment #2)

[snip]

Since this is a new API, we should let the Tor Browser be aware of it.
Once we confirmed it's a fingerprinting threat, we will file a new bug for
the protection work.

Anyone wondering that that bug is, it's bug 1461454.