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[whatwg] Stream API Feedback

From: Lachlan Hunt <lachlan.hunt@lachy.id.au>
Date: Mon, 14 Mar 2011 17:59:00 +0100
Message-ID: <4D7E4954.7000009@lachy.id.au>
   There are a few issues with the recently added media streaming API.

The IDL for GeneratedStream should indicate that it inherits from the 
Stream interface.

The API includes both readystatechange event, as well as independent 
events for play, paused and ended.  This redundancy is unnecessary. This 
is also inconsistent with the design of the HTMLMediaElement API, which 
does not include a readystatechange event in favour on separate events only.

The API does not provide any way for the author to indicate a preferred 
camera.  Some devices include multiple cameras, particularly phones with 
front and rear facing cameras, and some use cases are better suited to 
one or the other.

For example, an augmented reality application that takes advantage of 
geolocation and device orientation in order to overlay the video stream 
with things (e.g. push pins to identify points of interest, like on 
Google Street View). Such an application would be better suited for 
working with the rear facing camera.  But with a video conferencing 
application, the front facing camera would be more suitable.

It might therefore be useful for the author to provide a hint to this 
effect, which would allow the UA to more intelligently select the 
default camera for the user.

There are some use cases for which it would be useful to know the 
precise orientation of the camera, such as augmented reality 
applications.  The camera orientation may be independent of the device's 
orientation, and so the existing device orientation API may not be 

In the simple case, the front and rear cameras face in opposite 
directions, and so if an augmented reality application was built 
assuming it was using the rear camera, but the user instead granted 
access to the front camera, the calculations would be 180? out.

Some devices may also provide cameras that may allow the camera to be 
rotated independently of the device itself, and so camera orientation 
information would need to allow for this.  I don't know the best way to 
provide this, and there likely to be issues about whether the camera 
orientation should be relative to the device itself, or relative to 
fixed Earth coordinates (North, East, Up), like the existing device 
orientation API.

Lachlan Hunt - Opera Software
Received on Monday, 14 March 2011 09:59:00 UTC

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