[whatwg] media element playback rates
ian at hixie.ch
Fri Nov 2 10:34:13 PDT 2007
On Fri, 2 Nov 2007, Dave Singer wrote:
> About playbackRate and defaultPlaybackRate in the current specification of
> media elements, the logic that's currently necessary to set a media element to
> play at rate n is somewhat convoluted:
> If the media is paused
> 1) Set the defaultPlaybackRate to n.
> 2) Issue play().
> If the media is not paused
> - Set the playbackRate to n.
> And there's a distinct lack of permanence to setting playbackRate on
> playing media to alter its rate. Once media is paused, the play() method
> will reset the rate of the media (and playbackRate itself) to
> defaultPlaybackRate instead of to the previous value of playbackRate,
> which we think is unexpected.
The current design is built around three use cases:
1. Being able to implement fast-forward, rewind, or slow-motion easily.
2. Being able to change the playback rate for watching videos quickly.
3. Being able to do both in the same player.
In the current model:
Fast-forward and rewind just consists of calling play() to ensure the
playback head is moving and then changing 'playbackRate', resetting to
normal is just a call to play(); changing the default playback rate
without affecting that consists of changing 'defaultPlaybackRate' and, if
the UA isn't in a fast-forward, rewind, or slow-motion mode, and isn't
paused, also calling 'play()'.
We could optimise this by making defaultPlaybackRate affect playbackRate
if playbackRate == old_defaultPlaybackRate, though. Would that work?
> Similarly, the logic required to determine the rate at which media is
> playing or is about to play is convoluted. When listening for ratechange
> events, scripts must perform different checks depending on whether the
> media is currently playing.
Why? playbackRate always represents the current playback rate.
We could make changing defaultPlaybackRate when the content is paused
affect playbackRate, though. Would that work?
> Proposal: [...]
As far as I can tell this would significantly complicate implementing the
two use cases mentioned above together.
Ian Hickson U+1047E )\._.,--....,'``. fL
http://ln.hixie.ch/ U+263A /, _.. \ _\ ;`._ ,.
Things that are impossible just take longer. `._.-(,_..'--(,_..'`-.;.'
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