W3C home > Mailing lists > Public > whatwg@whatwg.org > November 2008

[whatwg] media elements: Relative seeking

From: Calogero Alex Baldacchino <alex.baldacchino@email.it>
Date: Mon, 24 Nov 2008 23:46:55 +0100
Message-ID: <1a9dab7e7c85cc84fc3533193cc2895a@>

--------- Original Message --------

 Da: "Maik Merten" &lt;maikmerten at googlemail.com&gt;

 To: "WHATWG Proposals" &lt;whatwg at lists.whatwg.org&gt;

 Oggetto: Re: [whatwg] media elements: Relative seeking

 Data: 24/11/08 08:45


&gt; Eric Carlson schrieb:

 &gt;&gt; QuickTime has used this method this since it started supporting

 &gt;&gt; mp3 in 2000, and in practice it works quite well. I am sure that

 &gt;&gt; are degenerate cases where the initial estimate is way off, but 

 &gt;&gt; generally it is accurate enough that it isn't a problem. An

 &gt;&gt; estimate is more likely to be wrong for a very long file, but each

 &gt;&gt; represents a larger amount of time in the time slider with a long 

 &gt;&gt; duration so changes less noticeable.


 &gt; Well, I do believe this works fine for audio (which usually hasn't a 

 &gt; wildly fluctuating bitrate if you e.g. average over a second or two), 

 &gt; I'm mostly concerned about video. An example for an outrageously off 

 &gt; estimate would be the trailer for "Generic space-pirate movie".


 &gt; The first few seconds would be mostly a static

 &gt; screen ("This pirate movie has been rated ARRRRRR!") - this part would

 &gt; be coded with like 100 kbit/s or less. The next few scenes (this is a 

 &gt; trailer, after all) would mostly show exploding ships, genetically 

 &gt; engineered mutant parrots attacking space-adventurers and a few cuts 

 &gt; into random love scenes - so this part can be multi-megabit/s. After 

 &gt; this the bitrate would dramatically decrease again as the last few 

 &gt; seconds will just show "Summer 2010". &gt;

&gt; Does QuickTime also handle such content gracefully (e.g. display a 

 &gt; position slider that doesn't jump around wildly)? Am I overestimating 

 &gt; the problem?


&gt; Maik

The slider should just indicate a relative position (i.e. a percentage)
between 0 and the (currently known) duration of the content, which may be
estimated with a variable average time, perhaps retarded at the beginning,
and varied according to the bitrate variation with some euristic, to make
the computation more accurate (or maybe a few consecutive evaluation, at
fixed and rapid intervals, could be averaged to get a better value, before
updating anything), so no "crazy horse jumping" should happen. Silvia
Pfeiffer has proposed a 'length' attribute to indicate the overall duration
in the markup, and I think its value could help to improve accuracy, even
when wrong.

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