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[Bug 15318] New: Define media.preservePitch attribute

From: <bugzilla@jessica.w3.org>
Date: Fri, 23 Dec 2011 00:02:34 +0000
To: public-html@w3.org
Message-ID: <bug-15318-2495@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=15318

           Summary: Define media.preservePitch attribute
           Product: HTML WG
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: HTML5 spec (editor: Ian Hickson)
        AssignedTo: ian@hixie.ch
        ReportedBy: giles@mozilla.com
         QAContact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-wg-issue-tracking@w3.org,
                    public-html@w3.org


HTML media elements have a playbackRate attribute which can be used to adjust
the playback rate. For video this just involves changing the display rate for
frames. For audio the situation is more complicated.

The simplest method is to resampling the audio relative to the audio device's
playback rate. This results in a pitch shift: playbackRate > 1.5 or so is high
and squeeky, playbackRate < 0.8 is low and echo-y. There are also more
sophisticated methods which attempt to preserve the spectral character so that
perceived pitches are preserved, though usually with some reduction in fidelity
where music is concerned.

There are reasonable use cases for both pitch-preserving and pitch-shifting
cases, and the specification currently leaves the decision to implementors.

Apple initially implemented the pitch-preserving case, but later added a
'webkitPreservesPitch' boolean attribute to control this choice.[1]

Looking at how we'd support playbackRate in Firefox, we found this a useful
distinction and suggest such an attribute be added to the specification. e.g.:

interface HTMLMediaElement : HTMLElement {
    attribute boolean preservePitch;
};

The element could default to true, since this is the less objectional behaviour
and is compabtible with webkitPreservesPitch.

[1] http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-July/021100.html

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Received on Friday, 23 December 2011 02:33:55 UTC

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