Re: [Hls-interest] HLS Content Steering v1.0b1 preliminary specification

[Roger Pantos <[e-mail]>]

> On Feb 17, 2021, at 1:46 PM, Pieter-Jan Speelmans <[e-mail]> wrote:
> 
> Hi all
> 
> I am pretty concerned about the backwards compatibility problems when attempting to use this in combination with older devices. It will force services to either provide two playlists, one with and one without EXT-X-DEFINE with client-side detection of the maximum version supported by the client. While this will not be an issue for up to date Apple devices, this will definitely be an issue for out of date devices but also most smart TVs, Chromecasts, Airplay implementations by those other than Apple (f.e. on LG), ...

Well, we’re still early enough that we could consider changing the format. I’m not particularly moved by the hardship of supporting EXT-X-DEFINE — anybody who is implementing content steering is going to have to do at least that much work in their m3u8 parsing anyway — but I acknowledge that requiring content vendors to provide a different master playlists for old, un-updated clients is a non-trivial burden.

What if we took the following approach instead?

First, add a new STEERING attribute to regular EXT-X-STREAM and MEDIA tags:

#EXT-X-STREAM-INF:BANDWIDTH=200000,STEERING=“1”
https://a.example.com/video/mid/index.m3u8 <https://a.example.com/video/mid/index.m3u8>

#EXT-X-STREAM-INF:BANDWIDTH=400000,STEERING=“1”
https://a.example.com/video/high/index.m3u8 <https://a.example.com/video/high/index.m3u8>

This links the variants (and renditions) to a steering template definition:

#EXT-X-STEERING-TEMPLATE:ID=“1”,PREFIX="https://a.example.com/video <https://a.example.com/video>”

#EXT-X-CONTENT-STEERING:SERVER-URI="/steering?video=00001",PATHWAY-ID="My-Great-CDN"

The manifest would change a bit:

{
   "VERSION": 0
   "TTL": 300,
   "RELOAD-URI": "https://example.com/steering?video=00001&session=123",
   "PATHWAYS": [
       {
		"ID": "My-Great-CDN",
		"TEMPLATES": {
		   "1" : { 
			“PREFIX”: "https://a.example.com/video" 
		   }
		}
       },
       {
		"ID": "My-Backup-CDN",
		"TEMPLATES": {
		   "1" : { 
			“PREFIX”: "https://b.example.com/backup-video" 
		   }
		}
       }
   ]
}

The client would load and play the master playlist as usual. When it parsed the EXT-X-STREAM-INF and EXT-X-MEDIA tags it would see the STEERING attribute and verify that there is a corresponding EXT-X-STEERING-TEMPLATE and that the PREFIX of the steering template matches the start of the URI (fatal error if either check fails). It would store away the remainder of the URI as the “steerable part.”

When it loaded the manifest it would check that each pathway had an object in its TEMPLATES object for each STEERING-TEMPLATE (matching the key to the ID). (If it did not, steering would be disabled.)

To switch pathways it would concatenate the PREFIX from the TEMPLATES object with the steerable part of each URI. After that, everything would behave the same way.

This approach isn’t as flexible as general variable substitution. But I think that it would still cover the majority of the substitution use cases (and I’d be interested to hear about those that it doesn’t).


Roger.

> 
> My personal opinion is that the value of backwards compatibility would warrant the drawbacks I currently see. 
> 
> Best regards,
> Pieter-Jan
> 
> 
> Pieter-Jan Speelmans
> CTO
> 
> THEO Technologies NV
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> 
> On Wed, Feb 17, 2021 at 9:57 PM Roger Pantos <rpantos=[e-mail] <mailto:[e-mail]>> wrote:
> Hello hls-interest,
> 
> As discussed on the call today, here is the preliminary specification for the new Content Steering feature. We are converging on the final design for 1.0, so please take a look at it when you can and tell us what you think. 
> 
> You can send feedback to this list, or to [e-mail] <mailto:[e-mail]> if you want it to go directly to us.
> 
> 
> 
> 
> regards,
> 
> Roger Pantos
> Apple Inc.-- 
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