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Re: Survey ready on Media Multitrack API proposal

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Thu, 4 Mar 2010 14:45:43 +1100
Message-ID: <2c0e02831003031945t6cc55437hd77de25fba9807f3@mail.gmail.com>
To: Maciej Stachowiak <mjs@apple.com>
Cc: Eric Carlson <eric.carlson@apple.com>, "Michael(tm) Smith" <mike@w3.org>, HTML Accessibility Task Force <public-html-a11y@w3.org>
On Thu, Mar 4, 2010 at 2:27 PM, Maciej Stachowiak <mjs@apple.com> wrote:
>
> On Mar 3, 2010, at 12:40 PM, Silvia Pfeiffer wrote:
>
>> On Thu, Mar 4, 2010 at 3:33 AM, Eric Carlson <eric.carlson@apple.com>
>> wrote:
>>>
>>> On Mar 2, 2010, at 11:14 PM, Silvia Pfeiffer wrote:
>>>
>>>>>
>>>>> You also didn't answer my second question -  are track names typically
>>>>> unique? Do media container formats generally guarantee the presence of
>>>>> unique track names?
>>>>
>>>> There is no guarantee of their existence - same for the role
>>>> attribute. But where they exist, they are unique.
>>>>
>>>  Track IDs (which are numeric) in QuickTime and MPEG-4 files are
>>> guaranteed to be unique, track names are not required and are *not*
>>> guaranteed to be unique.
>>
>>
>> So maybe for MPEG the track ID is the one that should be mapped to the
>> this field here as text? Or alternatively it could be a combination of
>> track name and the track ID?
>
> It seems like you can always provide a numeric indexing API to the tracks
> regardless of the media format. How about we make that the primary way to
> query for a track, and leave the name as an informative field?
>
> Using a numeric ID as a string name would be particularly confusing with the
> proposed API, since there are both name and index getters. Let's say you
> have a track that is first in the MediaTracks list, and it has a numeric
> track ID of "2".
>
> You might expect that myVideoElement.tracks["2"] will get the track with ID
> 2. But it will instead get the third track in the tracks list. That's
> because index getters take priority over name getters, and
>  myVideoElement.tracks[2] means the same thing as
>  myVideoElement.tracks["2"] in JavaScript. For this reason, it is a bad idea
> to provide both index getters and name getters when the names may be
> numeric.
>
> I suggest that we drop the name getter, since the index getter is more
> fundamental. No matter what kind of query you want to do, you can alway loop
> over all the tracks using tracks.length and the tracks index getter.

OK, I see the problem. I didn't consider that JavaScript converts sees
no difference in [2] and ["2"].

I have no issue with removing the getter on namedItem. I don't think
it's important.
The other getter already does the index by number.


Cheers,
Silvia.
Received on Thursday, 4 March 2010 03:46:37 GMT

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