W3C home > Mailing lists > Public > public-media-capture@w3.org > August 2012

Comments to requirements

From: Stefan Hakansson LK <stefan.lk.hakansson@ericsson.com>
Date: Thu, 23 Aug 2012 14:25:24 +0200
Message-ID: <50362134.2070106@ericsson.com>
To: "public-media-capture@w3.org" <public-media-capture@w3.org>
Back in July ([1]) Jim added requirements to the scenarios document.

Jim, many thanks for doing that, and apologies for not giving any 
feedback until now.

I think this looks generally good. I have some comments to some of the 
requirement, and propose that some requirements in the webrtc req 
document should perhaps also be added here. See below.


Some comments on the requirements in the current draft

     3. The UA must request the user's permission before sending or 
receiving a media stream to or from another user.
-- I am not sure this is a relevant requirement. The model, as I've 
understood it, is that the permission model asks only for permission to 
access user media. From there the user has to trust the app; it could 
send a media stream to a peer - or it could record to a file and send 


     2. The UA must be able to provide a visual display of the 
properties of the sound captured from from a microphone (volume in this 

-- In the webrtc/rtcweb use-case+req document [2] there is an associated 
requirement "F15: The browser MUST be able to change the level in audio 
streams." and API req A15 saying that the app must be able to control 
how the browser changes the level. Is that something we should add?

     5. The UA must be able to continue sending and/or capturing media 
while the tab is in the background.
-- This applies to receiving and rendering as well (if you're in a 
videochat, you'd not like the incoming audio to stop being played if you 
switch tab)
     6. The UA must be able to extract image frames from video.
     7. The UA must be able to insert image frames into a local video 
stream (or capture).

-- For the above two, have we at all discussed how to solve them? The 
text in the use case mentions the canvas element (to draw a box around 
the blue ball) but how would you go from that to a video stream?

     8. The UA must support the use of the local screen/display as a 
video source.

-- Agree, but a recorded video should also be allowed to use (the user 
should be able to trick the app by selecting a file - that has been 
recorded - as video source in the getUserMedia dialogue)

     The UA must allow the user to pause or stop media streams via UXes 
(and not just the buttons on the underlying hardware.)
-- There are two UXes: one is the browser chrome, the other is what the 
app provides. Both should be possible to use for "pause" (if the app has 
a pause button), but the chrome method must override the app


     1. The UA must be able to transmit media to one or more remote 
sites and to receive media from them.

-- A nit: is "sites" the right word? It gets me to think of things like 
origin, rather than a "peer" browser.
     2. The UA must be able to offer a preview of audio and video media 
received from a remote site.

-- What does "preview" mean in this context?

     5. The UA must be able to send or receive a still image over a 
video stream.
-- I can see this coming out of the scenario 2.5, but would not a more 
natural way to handle this be to send the actual picture to all 
participants for display using http or ws?

     7. Ability for user simply drag a image over a area of website, so 
the image is send to all of the other users
-- Again, something that can easily be accomplished even without 
MediaStreams of webrtc - I don't think we should add it

Media Capture

     5. the UA must enable the Application to set size contraints and 
time limits on media capture.
-- Do we really want the app to be able to define constraints in MBs?

     7. The UA must enable the Application to use device properties, 
such as battery level, to determine when to terminate media capture.
-- At least battery level seems out of scope for this TF - isn't that 
DAP turf?

Requirements in the webrtc req doc [2] that might make sense to add in 
this document
F8/A11: the UA must detect when a remote stream is not received any more 
(and inform the application)

F9: Echo handling must be supported by UA

F10: Support synchronous playout of audio and video

F18: Support playout of other audio at the same time as an audio stream 
is played

A19: Support for handling general audio different from speech (e.g. 
switch off noise reduction)

Received on Thursday, 23 August 2012 12:25:48 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 16:26:11 UTC