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

[Pieter-Jan Speelmans <[e-mail]>]

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this will definitely be an issue for out of date devices but also most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), ...

One option which could avoid this would be the following approach:
- Leverage the STABLE-VARIANT-ID and STABLE-RENDITION-ID identifiers to
modify an attribute of the Variant or Rendition.
- Allow a Variant or Rendition to be referenced in the Steering Manifest
with an updated value for the relevant attribute.
- Give the EXT-X-CONTENT-STEERING tag a MODIFIES attribute to list the
Variants and Renditions which will be modified and VARIANT-ATTRIBUTES and
RENDITION-ATTRIBUTES attributes to list the attributes which can be
modified rather than the DEFINES attribute.

The language for a Pathway would be defined as:

> {
>     "ID": string, // REQUIRED
>     "VARIANTS": { // REQUIRED
>
        "<STABLE-VARIANT-ID>": { // one for every variant listed to be
> modified

            Key-Value pairs for every attribute which you want to redefine
>
        }

    },
>
    "RENDITIONS": { // OPTIONAL

        "<STABLE-RENDITION-ID>": {  // one for every rendition listed as to
> be modified

            Key-Value pairs for every attribute which you want to redefine
>
        }

    }

}


For example this could make the Master Playlist.

> #EXTM3U
> #EXT-X-VERSION:8
>
>
> #EXT-X-CONTENT-STEERING:MODIFIED="VARIANT-1,VARIANT-2",VARIANT-ATTRIBUTES="URI",SERVER-URI="/steering?video=00001",PATHWAY-ID="My-Great-CDN"



#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="avc1.640028",STABLE-VARIANT-ID="VARIANT-1"
> https://cdn-a.example.com/low/main/audio-video.m3u8
>
> #EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="avc1.640028",STABLE-VARIANT-ID="VARIANT-2"
> https://cdn-a.example.com/hi/main/audio-video.m3u8


Which results into a Steering Manifest like the one below.

> {
>     "TTL": 300,
>     "RELOAD-URI": "https://example.com/steering?video=00001&session=123",
>     "PATHWAYS": [
>         {
>             "ID": "My-Great-CDN",
>             "VARIANTS": {
>                 "VARIANT-1": {
>                     "URI": "
> https://cdn-a.example.com/low/main/audio-video.m3u8"
>                 }
>                 "VARIANT-2":{
>                     "URI": "
> https://cdn-a.example.com/hi/main/audio-video.m3u8"
>                 }
>             }
>         },
>         {
>             "ID": "My-Backup-CDN",
>             "VARIANTS": {
>                 "VARIANT-1":{
>                     "URI": "
> https://cdn-b.example.com/low/main/audio-video.m3u8"
>                 }
>                 "VARIANT-2":{
>                     "URI": "
> https://cdn-b.example.com/hi/main/audio-video.m3u8"
>                 }
>             }
>         }
>     ]
> }


Benefits:
- Fully backwards compatible. Older clients will simply ignore the new
EXT-X-CONTENT-STEERING tag, and use the primary source.
- No change needed to the Master Playlist other than the addition of
the #EXT-X-CONTENT-STEERING tag.
- Also compatible with the AUTH-case for EXT-X-DEFINE by allowing the
Variable Substitution on attributes after retrieval from the Steering
Manifest
- As an added bonus, for those who are modifying the master playlist
anyway, the use of STABLE-VARIANT-ID and STABLE-RENDITION-ID allows clients
to identify and identify the Variants and Renditions.

Drawback:
- More closely coupled with HLS, making reuse of the Steering Manifest for
other failover cases less likely.

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*
*w *| www.theoplayer.com
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On Wed, Feb 17, 2021 at 9:57 PM Roger Pantos <rpantos=
[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] if you want it to go directly
> to us.
>
>
>
>
> regards,
>
> Roger Pantos
> Apple Inc.--
> Hls-interest mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/hls-interest
>

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