Re: UAAG 2.0 guidelines for video

On Wed, May 5, 2010 at 12:04 AM, Eric Carlson <> wrote:
> On May 4, 2010, at 6:56 PM, Janina Sajka wrote:
>> Silvia Pfeiffer writes:
>>> Correction to my previous email:
>>> The HTML5 media elements already have an attribute to control the playback rate:
>>>           attribute float defaultPlaybackRate;
>>> (see
>> Well, since we're a W3C working group, I think we're looking at:
>> Glad to see it's there, but not sure whether it's complete per the UAWG
>> requirements:
>> *     I don't see a supported range. UAWG wanted .5 to 2.0, which is
>> *     not particularly large.
>> *     I also believe we have a requirement for maintaining pitch
>> *     during the time-scale modification. Perhaps that's what the
>> *     editor's drft means when it says "monotonically," though I'm not
>> *     sure that's the best terminology.
>> In my opinion this will be an important feature for I18N as well as A11Y
>> support. For instance, anyone listening to content not in their native
>> language will doubtless discover enhanced comprehension by reducing
>> playback rate--provided pitch is maintained and no negative artifacts
>> are produced by the transformation.
>  I don't think we will be able to make pitch correction a MUST requirement as it is *extremely* computationally expensive and will likely not be possible - at all - on all supported hardware configurations.

Pitch maintenance during audio speed up and slow down is currently
supported in Windows Media Player, the Quicktime player, many MP3
players including the iPod (look under audio book and podcast
playback), and DAISY players ranging from desktop to small hardware
devices.  There may be some devices in which support will be difficult
and may not be advisable, but it would appear for the vast majority to
be (and is) possible.


Received on Wednesday, 5 May 2010 04:35:10 UTC