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Re: [AVT] Comments on draft-pantos-http-live-streaming-00.txt ...

<L.Wood@surrey.ac.uk> Fri, 22 May 2009 06:11 UTC

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From: L.Wood@surrey.ac.uk
To: john.lazzaro@gmail.com, avt@ietf.org
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Subject: Re: [AVT] Comments on draft-pantos-http-live-streaming-00.txt ...
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http://tools.ietf.org/id/draft-pantos-http-live-streaming-00.txt

There's a mismatch between the goal in the first sentence of
the introduction:

   This document describes a protocol for transmitting unbounded streams
   of multimedia data over HTTP [RFC2616].

and the focus of this draft on actually being limited to using
M3U files.

For unbounded streams where the length is not known a priori,
I was expecting to see heavy use of HTTP chunking.
That is not the problem that this draft is
trying to solve.

   Each media file URI MUST be preceded by an
   EXTINF tag.  Its format is:

   #EXTINF:<duration>,<title>

   "duration" is an integer that specifies the duration of the media
   file in seconds.  

So it's necessary to know how long a file is before specifying it.
The draft is not really dealing with an unbounded stream of data,
more bringing together separate known resources seamlessly. As John
says, that particular problem has been solved by AJAX.

cheers,

L.

<http://www.ee.surrey.ac.uk/Personal/L.Wood/><L.Wood@surrey.ac.uk>



-----Original Message-----
From: avt-bounces@ietf.org on behalf of John Lazzaro
Sent: Thu 2009-05-21 22:46
To: avt@ietf.org
Subject: [AVT] Comments on draft-pantos-http-live-streaming-00.txt ...
 
Hi everyone,

Comments on draft-pantos-http-live-streaming-00.txt below.

What jumped out at me was that this is a late-1990s
approach to a problem ... but its almost 2010 ...

In my view, the I-D is trying to do for audio what the AJAX client code
for Google Maps does for image map tiles. Namely, pre-loading short
media files over HTTP, to drive a user interface that the user
perceives as continuous (and in the Google Maps case,
responsive to user input).

I haven't looked at HTML5 (yet), but I was under the impression
one goal of its audio/video features is to provide the
primitives to make it possible to implement the protocol
described in draft-pantos-http-live-streaming-00.txt using
AJAX techniques.  If the feature set isn't there yet in HTML5
to do that, I think the time spent working on this I-D is better
spent working within the HTML5 process to get the features that
are needed.  It seems to me that AJAX is a more natural way to
implement this sort of "concatenation of pre-downloaded 10-second
files" streaming.

If there is AVT consensus that draft-pantos-http-live-streaming-00.txt's
general approach is acceptable for a work-item, I'll do a second review
of potential technical issues with the protocol itself ...

-- 
John Lazzaro
http://www.cs.berkeley.edu/~lazzaro
john [dot] lazzaro [at] gmail [dot] com

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