[whatwg] Video : Slow motion, fast forward effects

Charles Iliya Krempeaux supercanadian at gmail.com
Thu Aug 7 12:23:00 PDT 2008


On Thu, Aug 7, 2008 at 12:11 PM, Jonas Sicking <jonas at sicking.cc> wrote:

> Dave Singer wrote:
>> At 20:10  +1200 7/08/08, Chris Double wrote:
>>> On Thu, Aug 7, 2008 at 6:20 PM, Ian Hickson <ian at hixie.ch> wrote:
>>>>  On Thu, 7 Aug 2008, Biju Gm at il wrote:
>>>>>  On Thu, Aug 7, 2008 at 1:49 AM, Ian Hickson <ian at hixie.ch> wrote:
>>>>>  > playbackRate is the right way to do it, but maybe Firefox doesn't
>>>>> yet
>>>>>  > support it.
>>>>>  So can I assume HTML5 spec also allow playbackRate  to be negative
>>>>> value.
>>>>>  ie to support go backward at various speed....
>>>>  Yes.
>>> Would you expect the audio to be played backwards too?
>> I think that's extra credit and optional.  As you say, even with audio
>> coded in independent frames you have to flip the samples, which is a pain.
>>  For audio with forward dependencies, correct decoding means decoding
>> forwards and then flipping whole chunks of timeline (though AAC doesn't
>> suffer too badly if you don't do this, by the way).
> Honestly, this seems useless enough that the spec should just say that when
> playback is less than 0 sound should be turned off. I'd hate to see
> engineers working on this just because "the spec says it should work that
> way".

I don't think turning sound off is a good idea.

This feature would be used to implement "scrubing".  Like what you see in
Non-Linear Editors... for making movies, etc.  (I.e., grabbing the "position
handle" of the player, and moving it forwards and backwards through the
video, and varying speeds, to find what you are looking for.)

In those types of applications, the audio is on.  And it is important for
usability, for the video editor to hear the sound.

Charles Iliya Krempeaux, B.Sc.
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