W3C home > Mailing lists > Public > ietf-http-wg@w3.org > July to September 2009

Re: iPhone streaming Internet-Draft posted

From: David Singer <singer@apple.com>
Date: Wed, 29 Jul 2009 16:27:51 -0700
Message-Id: <p06240870c6968af572dd@[17.202.35.52]>
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 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Friday, 27 April 2012 06:51:08 GMT