W3C

- DRAFT -

HTMLCue breakout, TPAC 2015

28 Oct 2015

See also: IRC log

Attendees

Present
nigel, hober, Jean-Claude_Dufourd, giuseppe, JP, Abello, Giri, Mandyam, Kurosawa, Taketoshi, Yamane, Kinji, Matsumura, Akitsugu, Baba, glenn_adams, jerry_smith
Regrets
Chair
nigel
Scribe
giuseppe

Contents


<gmandyam> Giri Mandyam, Qualcomm, joining HTMLCue breakout session

cribe: giuseppe

<scribe> scribe: giuseppe

Nigel: in the TTWG we are looking at two formats

TTML and WebVTT

for webvtt we have a cue, with in/out and style

when we look at other formats

we are asking ourselves how we implement them in the rbrowser

dash.js is trying to use texttrackcue to support other tt formats

but to do that you need to overload the texttrackcue interface

because that is not designed to handle something else then webvtt

the question is why do we need a specific vtt cue, can we have a more generic cue mechanism that can support more formats

for example can we have an html cue

that only have in/out and an html payload

that the browser can attach that html payload on in/out

or better attach on in, remove on out

the idea with texttrack is to separate matadata in different tracks

in ttml structure mixes different things in one format (text and style and metadata)

status of this is that htmlcue is an idea

ttwg presented the idea to the whatwg

the feedback was there could be some unintended consequences

example what happens if the html contains a script

or what happens to the browser context

so I'm interested to discuss these issues and how to appraoch the problem

giuseppe: is the main goal here to support ttml?

nigel: yes mainly, but not only

ttml could be one source of information for the htmlcue track

simon: one issue with this

is security, if you allow all html in the htmlcue

subtitles usually don't have scripting

the other issue is if we assume thatw e need to subset html, does it still support the use cases you want to address

currently with wbvtt you can use a metadata track

and you can use javascript and render it

and there you don't have the security problem

why can't you use the webvtt metadata track and expose ttml then render in the page?

giri: the problem is, the html spec allows for 250ms delay
... and this might be an issue for things like subtitles

giuseppe: does it mean we need a high priority cue?

simon: are you sure this delay of 250ms apply to the cues?

(room checking the spec)

nigel: so the requirement is that accuracy has to be greater then 250ms

simon: the 250ms is only for the timesupdate

but should not apply to the cues

jc: cyril has done a demo using the events

x1: the secureity issue here i major

maybe is better to look at extending the current api

giri: what about the idea of using a sandbox

nigel: you could block any script and maybe threat it like an iframe

simon: the metadata kind is designed to support this use case

xxx: could there be a problem of performance, is the html is too complex?

jc: maybe you can do some testing and show if there is really a performance problem, and if you really need some htmlcue

nigel: so the proposed model is to use existing track cue with metadata kind, although is not metadata, and then render in javascript

xxx: there are of course some problems

for example the browse might need to expose the subtitles preferences

so that the js renderer know what to do

the other problem is that you cannot use the defaul player controller

but if you are doing this custom subtitlles handling you can probably build your custom controls as well

giri: what happens if kind is set to something other then the allowed values

simon: I think it defaul to subtitles

andreas: the question is still, wouldn't be better to have some easier way to support this

also, it it's easier for people to transalte from ttml to html then to vtt

because for webvtt you need to know both the sintax but also the renderin model that is different

all: discussion about if it's feasible to make a subset of html suitable for this htmlcue
... some people concerned that subsetting html has been done before and always failed

we should not try to do it again

nigel: isn't this very similar to sandboxing?

simon: one of the reason I think this si different, is because there is no way to disable fetching external resources, and I think we need that

nigel: why should we do that, images might be needed

simon: but then you might have a privacy issue

e.g. an external resource/server could now monitor videoplayout events, monitor what you watch

something that was not possible before (only the internal scripting of the page could do it)

xxx: the image issue could be solved using data: urls

<scribe> ACTION: file a feature request to expose user preferences about subtitles to the page [recorded in http://www.w3.org/2015/10/28-htmlcue-minutes.html#action01]

<scribe> ACTION: work on a prototype using the metadata kind for texttrack and to try and highlight limitation and issues [recorded in http://www.w3.org/2015/10/28-htmlcue-minutes.html#action02]

Summary of Action Items

[NEW] ACTION: file a feature request to expose user preferences about subtitles to the page [recorded in http://www.w3.org/2015/10/28-htmlcue-minutes.html#action01]
[NEW] ACTION: work on a prototype using the metadata kind for texttrack and to try and highlight limitation and issues [recorded in http://www.w3.org/2015/10/28-htmlcue-minutes.html#action02]
 
[End of minutes]

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$Date: 2015/10/28 03:04:16 $

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Present: nigel hober Jean-Claude_Dufourd giuseppe JP Abello Giri Mandyam Kurosawa Taketoshi Yamane Kinji Matsumura Akitsugu Baba glenn_adams jerry_smith
Got date from IRC log name: 28 Oct 2015
Guessing minutes URL: http://www.w3.org/2015/10/28-htmlcue-minutes.html
People with action items: file work

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<dbooth> Topic: Review of Amy's report


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