Re: ISSUE-335 (Negative times for offsets): In order to handle offsets between start time in TTML docs and start time in video, allow negative times to be used in fragment begin times. [TTML.next]

I think we should keep it open and add support for ttp:mediaTimeOffset
which could be negative.


On Fri, Aug 15, 2014 at 11:30 AM, Courtney Kennedy <ckennedy@apple.com>
wrote:

> Hi Nigel,
>
> Ok, we can close this then.
>
> Best Regards,
> Courtney
>
> Sent from my iPhone
>
> On Aug 15, 2014, at 9:03 AM, Nigel Megitt <nigel.megitt@bbc.co.uk> wrote:
>
>  Hi Courtney,
>
>  I agree it’s a real world situation, but I don’t understand why your
> proposal is better than just putting the TTML file through a transformation
> processor that adjusts all the times – hence my questions.
>
>  At the point when you know what offset value to put into the document
> you know what all the correct times should be, don’t you?
>
>  If yes, you can already solve this problem with TTML.
> If no, how do you assign the offset value?
>
>  Am I missing something extra?
>
>  Kind regards,
>
>  Nigel
>
>
>   From: Courtney Kennedy <ckennedy@apple.com>
> Date: Friday, 15 August 2014 16:31
> To: Nigel Megitt <nigel.megitt@bbc.co.uk>
> Cc: Timed Text Working Group <public-tt@w3.org>
> Subject: Re: ISSUE-335 (Negative times for offsets): In order to handle
> offsets between start time in TTML docs and start time in video, allow
> negative times to be used in fragment begin times. [TTML.next]
>
>   HI Nigel,
>
>  This is a real world situation that I have encountered with some
> content.  For whatever reason, the producers of the subtitles cannot use
> the same start time as the producers of the video and audio.  I think there
> is a benefit to have all the information within the subtitles file rather
> than having it in a sideband file which can get lost or separated from the
> subtitles file.
>
>  Best Regards,
> Courtney
>
>  On Aug 15, 2014, at 5:54 AM, Nigel Megitt <nigel.megitt@bbc.co.uk> wrote:
>
> Hi Courtney,
>
> I¹m puzzled by the implied workflow here: if the subtitle file and the
> video have been created, at what point is the subtitle file modified to
> include the new offset? And if someone or some system is making such an
> edit why not simply make the times in the TTML correct against the video,
> rather than adding an offset?
>
> I¹ve seen this issue arise before, when packaging TTML documents in ISO
> BMFF (or some other wrapper). In that case the packaging is likely to
> happen after production of all the media that would be wrapped so it seems
> like the best way to capture any offset is using the facilities provided
> by the wrapper rather than editing the content itself. Certainly ISO BMFF
> appears to offer enough parameters/attributes to support that use case.
>
> I guess the key structural point is that there is a need to signal
> equivalence of some time reference in the TTML with some other time
> reference in a specific rendition of some related media. At the moment
> this is expected to happen externally to the TTML document: why would we
> bring it inside the document, given that no explicit link exists from
> within a TTML 1 SE document to a related media object?
>
> Kind regards,
>
> Nigel
>
>
>
> On 14/08/2014 16:33, "Timed Text Working Group Issue Tracker"
> <sysbot+tracker@w3.org> wrote:
>
> ISSUE-335 (Negative times for offsets): In order to handle offsets
> between start time in TTML docs and start time in video, allow negative
> times to be used in fragment begin times. [TTML.next]
>
> http://www.w3.org/AudioVideo/TT/tracker/issues/335
>
> Raised by: Courtney Kennedy
> On product: TTML.next
>
> Use case:
>
> Subtitles files may be created separately from video and audio for any
> particular piece of content.  Subtitles may be created in different
> facilities and at different points in time than the original content.  As
> a result of this decoupling, sometimes the subtitles file will use a
> different start time than the video and audio.
>
> Proposal:
>
> Time expressions in sub-elements are relative to the time expressions in
> their parent elements, as described in section 10.2.4 of the TTML
> specification.
>
> When subtitles have non-zero start times relative to the video they are
> to be synchronized with, the parent div element can have an offset in the
> begin attribute which, when applied to the times in the samples within
> the div element, will produce time expressions that synchronize with
> video.
>
>
> The following example uses this offset to indicate that the titles are
> using start time of 01:00:00:00, and require adjustment before their
> values express the actual time they should appear in the video.
>
>
> <div begin="-01:00:00:00">
>  <p begin="01:00:05:00" end="01:00:10:00">
>  This text should appear at 00:00:05:00
>  </p>
> </div>
>
>
>
>
>
>
>
>    _____________________________________________
> Courtney Kennedy 408.974.3386, mobile: 408.771.8615
> Engineering Manager, Media Sharing
> Apple, Inc.
>
>
>
>
>
>