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Re: iPhone streaming Internet-Draft posted

From: David Singer <singer@apple.com>
Date: Wed, 29 Jul 2009 16:27:51 -0700
Message-Id: <p06240870c6968af572dd@[]>
To: Mark Nottingham <mnot@mnot.net>
Cc: HTTP Working Group <ietf-http-wg@w3.org>, http-live-streaming-review@group.apple.com
Hi Mark

sorry for being slow (vacations and travel etc.)

On Jul 15, 2009, at 11:00 PM, Mark Nottingham wrote:
>1) Can you speak to why you chose to do this by extending m3u, 
>rather than using HTTP's built-in partial content mechanism (ranges)?
>While you'd need to specify some metadata (e.g., headers to describe 
>where alternate encodings/bitrates can be found), this would be easy 
>to do, and would have the advantage of not requiring the server to 
>split up the file into multiple chunks at different URIs (an 
>administration and operations headache).
>The analogy that comes immediately to mind is PDFs; the approach 
>you're taking is roughly equivalent to Adobe saying that PDF files 
>should be split into a URI-per-page and then putting an index file 
>on the site to link to each page.

This approach doesn't work with CDNs, who don't support adding custom 
headers to HTTP responses and cannot cache a single 
infinitely-growing resource which is being supplied to them in real 
time (i.e. a live video stream).

On top of that, the client would depend on a single connection to a 
single server for the life of the presentation, which prevents 
load-balancing and makes failover considerably more difficult.

The playlist approach has a few other advantages. Using a playlist of 
segments gives the client enough information to switch between 
streams of different quality dynamically. It also allows the content 
provider to express a range of time in which a client may seek.

>2) Apple has disclosed IPR <https://datatracker.ietf.org/ipr/1142/> 
>for this draft.
>My layman's reading is that anyone who wants to host a stream using 
>this technique requires a written license from you, including the 
>possibility of paying a fee, once your patents are granted.
>Is there anything else we should know about this? As it is, (and 
>only speaking as an implementer), this just gives me more motivation 
>to use other techniques.

I'm not qualified to speak to the legal implications of the IPR 
disclosure. Note that we offered the QuickTime file format to ISO 
(for MPEG-4) under the same terms.  Send me direct email and I'll try 
to work with you to clarify this status.
David Singer
Multimedia Standards, Apple Inc.
Received on Wednesday, 29 July 2009 23:30:33 UTC

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