[Bug 25910] New: [WebVTT] A way to correct cues

https://www.w3.org/Bugs/Public/show_bug.cgi?id=25910

            Bug ID: 25910
           Summary: [WebVTT] A way to correct cues
           Product: TextTracks CG
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: WebVTT
          Assignee: dave.null@w3.org
          Reporter: self@brendanlong.com
        QA Contact: public-texttracks@w3.org
                CC: philipj@opera.com, silviapfeiffer1@gmail.com

*Why*

In streaming text tracks, we need a way to fix incorrect cues. Some 
examples:

  * In live TV, people type the captions in by hand
    <http://en.wikipedia.org/wiki/Closed_captioning#Television_and_video>
shortly
    before you see them. If they make a mistake, we need a way to fix it.
  * CEA-608 and CEA-708 captions don't start with a convenient startTime
    --> endTime block like WebVTT does. A caption ends when we get a
    command that makes it stop displaying. If we want to transcode to
    WebVTT in real-time, we have to either wait until the caption is
    over to translate it (delaying the stream by some arbitary time in
    the hope that it will be long enough), or we need to start a caption
    immediately with a guess of the end time and then rewrite it once we
    know the correct end time (or rewrite it to extend the end time
    until we find the correct one).

*How*

The solution I'm proposing is that if we see two cues with the same id, 
the earlier cue will be removed.

    some-id
    00:00:00 --> 00:00:30
    This is an xeample

    some-id
    00:00:00 --> 00:00:10
    This is an example

In this example, the text "This is an example" will be displayed for 10 
seconds starting at time 0.

*Why This Solution*

This solution is nice because the syntax is simple and easy to 
understand, and it's powerful enough to rewrite any cue in any way you 
could possibly want, because the new cue completely replaces the old one.

*Arguments against*

This isn't particularly efficient. If you just want to change the time, 
you need to send the entire updated cue, instead of just the change.

I don't think this is a big deal, because even the most heavily edited 
subtitle file will be orders of magnitude smaller than the accompanying 
video.

See:

http://lists.w3.org/Archives/Public/public-html/2014May/0020.html

I originally proposed doing this in HTML, but Philip convinced me that that's
not a good idea. Having the WebVTT parser should be easy though.

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Received on Wednesday, 28 May 2014 13:59:33 UTC