Re: Question about ttml times

On Fri, Aug 8, 2014 at 11:37 AM, Courtney Kennedy <ckennedy@apple.com>
wrote:

> Hi Everyone,
>
> I am working on code to translate between TTML and WebVTT.  I have a TTML
> sample file that expresses the times of samples in the
> hours:minutes:seconds:frames format.  But, the file has no indication of
> what the frame rate is.  So, what is the best practice for converting times
> from this format into other formats, in the absence of a frame rate?
>

In the absence of any explicitly specified ttp:* timing related parameters,
the following defaults apply:

ttp:timeBase="media"
ttp:frameRate=*default app frame rate*, or if none defined, then 30
ttp:frameRateMultiplier="1 1"
ttp:subFrameRate="1"

See specific parameter definitions under [1] for more details.

As for how to interpret *default app frame rate*, I would expect it to
evaluate to the frame rate of a related media object if defined, or, if not
defined, then a common region specific frame rate.

Now that I'm looking at this further, I suspect we need to be a bit more
flexible in allowing for an application default parameter for
frameRateMultiplier and subFrameRate in the case that an application
default is used for frameRate. I've created Issue 333 [2] to address this
point.

[1]
http://www.w3.org/TR/2013/REC-ttml1-20130924/#parameter-attribute-vocabulary
[2] https://www.w3.org/AudioVideo/TT/tracker/issues/333


>
> Thanks for any help,
> Courtney
>
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