WebVMT: Suggested Topics For TPAC Breakout Session

[rjksmith]

Identify suitable ideas for a WebVMT breakout session at TPAC in Lyons in October.

This is my first visit to TPAC and I'm looking for some guidance on relevant topics and objectives which are likely to attract interest and generate a constructive response from the Plenary Day audience.

[rjksmith]

Thanks for the offline guidance and discussion. I've summarised my proposal for the TPAC breakout session, and welcome any suggested amendments.

Metadata Cues For Video Including Geolocation

Key Stakeholders

1. Web browser developers involved with <video> and <track> support.
2. WebVTT contributors from the Timed Text Working Group.
3. Developers involved with video and location, e.g. dashcam.

Objectives & Outcomes

1. Determine the current status of WebVTT metadata cue support in web browsers.
2. Determine whether WebVTT metadata cues are suitable for WebVMT support.
3. Determine whether a new map cue is required for WebVMT.
4. Determine timescales for the proposed solution.

Content & Approach

1. Explain the purpose of WebVMT: presenting, sharing and indexing location with video on the web for the emerging market in mobile video devices.
2. Describe important use cases and identify key user communities, e.g. police.
3. Present technical demos and highlight their details.
4. Discuss solutions.

[tidoust]

One of the possible objectives, possibly coupled with 3., is to determine a suitable way to specify WebVMT. If the first objective is to be able to use <track> elements without requiring any change to user agents (as discussed in #1019), then it would be good to specify WebVMT as a subset of WebVTT, a WebVMT file being a WebVTT file that contains metadata cues, with WebVMT "simply" describing how to format and interpret the metadata text.

I note that the proposed solution does not allow that entirely because it defines TIMELINE and MAP blocks that are forbidden in WebVTT. I don't think WebVTT has a mechanism by which global parameters may be provided (and exposed to the underlying Web app!), but that could also be a specific topic for discussion with WebVTT folks.

[rjksmith]

I agree. It would be a natural progression for WebVMT to become a metadata format for WebVTT.

There are currently three key differences from WebVTT:

1. The cue end time has been made optional so cues can persist to the end of the file, which may be at an unknown time in the case of a stream. This isn't a common use case for subtitles, but is for map annotations. A possible WebVTT media container use case would be adding a logo to a video, in a similar way to channel logos on YouTube.

2. The TIMELINE block is also applicable to WebVTT, though perhaps less obvious. It could be used to search a video archive for a clip by keyword, either in subtitles or as a metadata category, and return video for the duration of the cue, c.f. search by location. Renaming this block to MEDIA may be a better choice.

3. The MAP block is simply a metadata initialisation mechanism which mirrors the STYLE block approach by preceding the first cue. This could be renamed INITIAL-METADATA with properties called map-center and map-zoom-radius to include more general cases.

In addition, the format could spawn an XML version for 'less-webby' applications, akin to TTML.

[rjksmith]

Having made a start on the data model and file format documentation, I realise that the MAP block needs to retained and cannot be generalised for arbitrary metadata initialisation, so please disregard item 3 in my previous comment.

[rjksmith]

I've added a proposal based on this discussion to the TPAC Session Ideas Wiki.

Further suggestions welcome.

[rjksmith]

A breakout session was successfully proposed and chaired on 24 October 2018 at TPAC Lyon, which is summarised in a w3c/strategy comment with slides and minutes.

Many thanks to all those who contributed.