Subject: Re: iPhone streaming Internet-Draft posted

From: David Singer <[email-masked]>
Date: Wed, 29 Jul 2009 16:27:51 -0700

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.

---

From: Mark Nottingham <[email-masked]>
Date: Thu, 30 Jul 2009 09:26:14 +0200

On 30/07/2009, at 1:27 AM, David Singer wrote:
> This approach doesn't work with CDNs, who don't support adding  
> custom headers to HTTP responses and cannot cache a single  

I assure you that they can and will find ways to address it if an  
approach like this is implemented widely; caching proxies generally  
already support range requests (and combining ranges) out of the box.  
Have you engaged with any to discuss this with them?

> single server for the life of the presentation, which prevents load- 
> balancing and makes failover considerably more difficult.

Nothing says that you have to make range requests on a single  
connection.

> The playlist approach has a few other advantages. Using a playlist  
> of segments gives the client enough information to switch between  

It would be extremely simple to add this information elsewhere; either  
in the format itself, or in headers.

>> only speaking as an implementer), this just gives me more  
>> motivation to use other techniques.
>
> (for MPEG-4) under the same terms.  Send me direct email and I'll  
> try to work with you to clarify this status.

Thanks, but I think it'd be better if Apple made a public statement  
about it, otherwise people will have the same concerns.

Cheers,

--
Mark Nottingham     http://www.mnot.net/