W3C home > Mailing lists > Public > public-media-capture-logs@w3.org > September 2016

[mediacapture-main] Camera light and "disabled"

From: Harald Alvestrand via GitHub <sysbot+gh@w3.org>
Date: Thu, 01 Sep 2016 09:36:18 +0000
To: public-media-capture-logs@w3.org
Message-ID: <issues.opened-174478906-1472722576-sysbot+gh@w3.org>
alvestrand has just created a new issue for 

== Camera light and "disabled" ==
In current implementations, we mainly use the camera light as an 
"on-air" indicator.

At the moment, the spec says:

Turning on:
If the result of the request is "granted", User Agents are encouraged 
to include a prominent indicator that the devices are "hot" (i.e. an 
"on-air" or "recording" indicator), as well as a "device accessible" 
indicator indicating that the page has been granted access to the 

Turning off:
A script can indicate that a MediaStreamTrack object no longer needs 
its source with the stop() method. When all tracks using a source have
 been stopped or ended by some other means, the source is 
stopped...... If the data is being generated from a live source (e.g.,
 a microphone or camera), then the User Agent should remove any active
 "on-air" indicator for that source.

A muted or disabled MediaStreamTrack renders either silence (audio), 
black frames (video), or a zero-information-content equivalent. For 
example, a video element sourced by a muted or disabled 
MediaStreamTrack (contained within a MediaStream ), is playing but the
 rendered content is the muted output. When all tracks connected to a 
source are muted or disabled, the "on-air" or "recording" indicator 
for that source can be turned off; when the track is no longer muted 
or disabled, it must be turned back on.

Disabling is a Javascript-controllable function, using the "enabled" 
attribute of a track.

(Note that it says "can be turned off" and "must be turned back on" - 
so keeping the light on is legal.)

Two worries with this wording:

- Privacy: Disabling the track and having the light go out leads to a 
malicious application being able to turn on the camera briefly to take
 a picture at any later time, possibly without the user noticing 
because the indicator flash is so brief.
- Practicality: For a certain class of drivers, turning the light off 
means closing the camera. Re-opening the camera will take significant 
cycles, and having the camera device released means losing what little
 guard we have against some other app stealing the camera while it's 

Suggestion: Change the language in the third quote above to read:

"When all tracks connected to a source are muted, the "on-air" or 
"recording" indicator for that source can be turned off; when the 
track is no longer muted, it must be turned back on.
When the track is disabled, but not muted, the "on-air" or "recording"
 indicator should still be on, to indicate that the device is still 
available to the application at any time."


Please view or discuss this issue at 
https://github.com/w3c/mediacapture-main/issues/389 using your GitHub 
Received on Thursday, 1 September 2016 09:36:28 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 16:27:30 UTC