[whatwg] media elements: Relative seeking
Calogero Alex Baldacchino
alex.baldacchino at email.it
Mon Nov 24 14:46:55 PST 2008
--------- Original Message --------
Da: "Maik Merten" <maikmerten at googlemail.com>
To: "WHATWG Proposals" <whatwg at lists.whatwg.org>
Oggetto: Re: [whatwg] media elements: Relative seeking
Data: 24/11/08 08:45
> Eric Carlson schrieb:
>> QuickTime has used this method this since it started supporting
>> mp3 in 2000, and in practice it works quite well. I am sure that
>> are degenerate cases where the initial estimate is way off, but
>> generally it is accurate enough that it isn't a problem. An
>> estimate is more likely to be wrong for a very long file, but each
>> represents a larger amount of time in the time slider with a long
>> duration so changes less noticeable.
> Well, I do believe this works fine for audio (which usually hasn't a
> wildly fluctuating bitrate if you e.g. average over a second or two),
> I'm mostly concerned about video. An example for an outrageously off
> estimate would be the trailer for "Generic space-pirate movie".
> The first few seconds would be mostly a static
> screen ("This pirate movie has been rated ARRRRRR!") - this part would
> be coded with like 100 kbit/s or less. The next few scenes (this is a
> trailer, after all) would mostly show exploding ships, genetically
> engineered mutant parrots attacking space-adventurers and a few cuts
> into random love scenes - so this part can be multi-megabit/s. After
> this the bitrate would dramatically decrease again as the last few
> seconds will just show "Summer 2010". >
> Does QuickTime also handle such content gracefully (e.g. display a
> position slider that doesn't jump around wildly)? Am I overestimating
> the problem?
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
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