#788: Review of IMSC-HRM

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Opened Nov 22, 2022

Wotcher TAG!

I'm requesting a

TAG review of IMSC-HRM

What it is

The IMSC Hypothetical Render Model (HRM) constrains the presentation processing complexity of subtitle and caption documents that conform to the IMSC Recommendation.

The HRM is not a new concept: it has been included in all versions and editions of the IMSC Recommendation and has remained substantially unchanged.

In order to simplify future maintenance, the TTWG wishes to refactor the HRM into its own Recommendation.

Key info

  • Explainer¹ (minimally containing user needs and example code): https://github.com/w3c/imsc-hrm/blob/main/misc/explainer.md
  • Specification URL: https://www.w3.org/TR/imsc-hrm/
  • Tests: will be located at https://github.com/w3c/imsc-hrm-tests when they have been created
  • User research: none specific to the IMSC-HRM
  • Security and Privacy self-review²: https://github.com/w3c/imsc-hrm/blob/main/misc/security-and-privacy.md
  • GitHub repo (if you prefer feedback filed there): https://github.com/w3c/imsc-hrm/
  • Primary contacts (and their relationship to the specification):
    • Nigel Megitt (@nigelmegitt), BBC (Chair, TTWG)
    • Pierre-Anthony Lemieux (@palemieux), Movielabs (Editor, IMSC-HRM)
    • Gary Katsevman (@gkatsev), Mux (Chair, TTWG)
  • Organization(s)/project(s) driving the specification: W3C TTWG
  • Key pieces of existing multi-stakeholder review or discussion of this specification: This specification has been published in IMSC Recommendations and has therefore gone through Wide Review and TAG review previously as part of those IMSC Recommendations. Usage of the IMSC-HRM to analyse real world subtitle and captions documents from a variety of sources has led to issues such as w3c/imsc-hrm#49.
  • External status/issue trackers for this specification (publicly visible, e.g. Chrome Status): None that we're aware of

Further details:

  • I have reviewed the TAG's Web Platform Design Principles
  • Relevant time constraints or deadlines: We would like to transition from WD to CR in the next 2-3 months if possible
  • The group where the work on this specification is currently being done: W3C TTWG
  • The group where standardization of this work is intended to be done (if current group is a community group or other incubation venue): same, W3C TTWG
  • Major unresolved issues with or opposition to this specification: None.
  • This work is being funded by: TTWG members

Also

You should also know that...

As part of Horizontal Review, we requested review from PING and Security based on the text at https://github.com/w3c/imsc-hrm/issues/19#issue-1073404996 . The self-questionnaire linked above was produced after that, and written to be in agreement with that text.

  • PING tracking issue: w3cping/privacy-request#65
  • Security tracking issue: w3c/security-request#18

One question we are considering is whether we should update existing IMSC Recommendations to remove the existing HRM text and then either to 1) normatively reference IMSC-HRM as a conformance requirement or 2) informatively reference the IMSC-HRM as an optional conformance requirement for users to decide on.

The goal of the IMSC-HRM is to set a maximum presentation complexity for subtitle and caption documents to maximise the likelihood that presentation processors will successfully produce an accessible experience for end users, in particular timely presentation. It is out of scope for IMSC-HRM to model or constrain readability complexity.

Feedback

We'd prefer the TAG provide feedback as:

🐛 open issues in our GitHub repo for each point of feedback

Discussions

2023-01-09

Minutes

Peter: conversations between them and the CSS WG

Amy: this spec was mentioned in the FO report - because this was the main reason they wanted to change the wording in the TTML charter... They talked me through it on a call so i understand the gist. A way to share info on what devices can render for subtitles - so not too much information is provided. It's a complicated spec to read.

Rossen: explainer highlights and does explain what they're doing and why. Based on the design they're proposing - the brief overview is - a level of capability categorization - allow them to understand what the time to render a subtitle is - so subtitles don't overlap. Fairly well scoped and well intended capability. Question I'm not understanding : as the author what will you do about it? If you have font specific ... as an author you should be able to switch and use something less expensive.

Amy: Also note: I understand none of the substance is new - it all existed as part of another spec before.

Dan: so there are presumably already implementations. Is there any revision? What's changed?

Rossen: visually there is change, but hard to see what

Peter: are they asking us to review the delta, the refactoring, or all of HRM? I don't recall that we've ever reviewed this in its entirety

Dan: could we ask... what the specific ask is. What should we be focussing on? What answers do you want from the TAG? Given it's already existing rec, is there anything architectural that you're concerned about that we should weigh in on?

Peter: are they really asking for a full TAG review of the HRM?

Amy: will leave a comment

2023-03-06

Minutes

some recap of the Council discussion

2023-05-15

Minutes

Hadley: did we not conclude that this doesn't have an impact on the architecture?

Amy: the issue is... this will get challenegd at CR by the AC... Is that our problem?

Hadley: we can say we've reviewed it and it doesn't have an arch impact- it doesn't say we can support.

Amy: no harm here.

<blockquote>

Thanks for this request. We've looked at the spec and had several conversations with you and the working group through the past few months. We don't see that this proposal has any impact on the architecture of the web, so we won't hold you up any further. We are really sorry this has taken so long!

</blockquote>