W3C home > Mailing lists > Public > uri@w3.org > June 2003

Re: temporal URI fragments

From: <Silvia.Pfeiffer@csiro.au>
Date: Thu, 26 Jun 2003 00:22:58 +1000
To: duerst@w3.org
Cc: Silvia.Pfeiffer@csiro.au, LMM@acm.org, uri@w3.org, Conrad.Parker@csiro.au
Message-ID: <3EF9B042.605@cmis.csiro.au>

Martin Duerst wrote:
> At 16:33 03/06/25 +1000, Silvia.Pfeiffer@csiro.au wrote:
>>> Why not make the fragment identifier independent of the sample
>>> rate? Aren't there situations where you might want to send
>>> different sample rates depending on the bandwidth of the
>>> connection? Or situations where there is timed data that isn't
>>> 'sampled'? I'm not sure why 'seconds, in floating point, to
>>> any accuracy desired' isn't a better design as far as interoperability
>>> might go.
>> Every time-continuous data stream is sampled when getting digitised 
>> and is usually sampled at a constant sampling rate (e.g. 44100 Hz for 
>> audio).
> But there are time-continuous data streams that are not sampled.
> Animation (e.g. SMIL animation or SVG animation) is a typical
> example. Your XML example also doesn't need to have a fixed
> sampling rate.

You're right. :) I was only thinking of time-continuous real-world 
signals that need digital conversions.

>> Now, for the fragment, the most generic way to identify a time offset 
>> is indeed 'seconds, in floating point, to any accuracy desired' and 
>> "npt" supports that. However, there are types of data for which people 
>> have found other ways for referencing temporal offsets.
> Of course there are other ways. But if there is one way that works
> in all cases, why make it unnecessarily complicated.

I guess, we came from the rtp/rtsp example and there all were supported.

> By the way, Larry wrote 'seconds, in floating point'. I think
> this should just be a decimal notation, not including exponents.

Hmm. What if the precision of a specific rational number is required?

>> The SMPTE fragment offsets are actually not dependent on the sampling 
>> rate of the digital video that they refer to, such that if there is a 
>> video sampled at e.g. 25 fps, you may still put a framgent offset of 
>> e.g. #@smpte-60=00:01:05.20 on it.
> Does that say it's sampled at 60 fps? or what?

Sorry, should have read: #@smpte-60=00:01:05

Yes, smpte-60 says that the time label is given as a label with 60 fps, 
i.e. the last number represents 5/60 seconds. This says nothing about 
the actual sampling rate of the video and only refers to the 
interpretation of the time format.

Received on Wednesday, 25 June 2003 10:22:51 UTC

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