W3C home > Mailing lists > Public > public-html@w3.org > December 2008

Re: HTMLMediaElement defaultPlaybackRate and playbackRate

From: Pierre-Olivier Latour <pol@apple.com>
Date: Mon, 1 Dec 2008 18:09:16 -0800
Cc: Eric Carlson <eric.carlson@apple.com>, HTML WG <public-html@w3.org>
Message-Id: <ECEE6E76-01DC-443F-AD8C-64053E8DB355@apple.com>
To: Ian Hickson <ian@hixie.ch>

> Now, consider this sequence of events:
>
>   1. User loads page, e.g. a presentation about penguins.
>   2. User tells the JS controller that he wants to view the video at  
> 1.2x
>      normal speed, so that he can view the presentation faster.
>   3. The video turns out to start with a long unrelated section.
>   4. User starts fast-forwarding to the point he wants to see, using  
> the
>      JS controller.
>   5. User switches to full-screen.
>   6. User gets to the place he's looking for and hits "play" in the UA
>      full-screen controller.
>
> The UA needs to know that the user wanted to play at 1.2x speed, not  
> ffwd
> speed. With defaultPlaybackRate, how can the JS controller tell the UA
> controller what speed to use?

Using the playback rate is not really a "clean" way to do FF: this is  
not very efficient and the audio is going to be horrible unless you  
temporarily mute (or the UA does it for you). Instead, you should have  
the playback temporarily paused and the playhead jump by X ms every Y  
ms as long as FF is active: this is the common way to do FF in digital  
media world (i.e. not tape based). Your DVD player likely does that,  
so does NetFlix streaming, etc...

Playback rate is more to do slow-motion or accelerated playback, jog  
shuttle control, etc...

Considering the above I still highly recommend we remove  
"defaultPlaybackRate" as it's no the right solution no matter what,  
and find a clean way to implement true FF playback DVD style which is  
2x, 4x, etc... (typically not 1.76x), has no audio, and skips frames.  
This certainly sounds like an important feature.

________________________________
Pierre-Olivier Latour - pol@apple.com
Rich Media Team - Apple, Inc.
Received on Tuesday, 2 December 2008 02:09:57 GMT

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