Re: TTML and aspect ratio

On Wed, Jan 30, 2013 at 10:31 AM, David Ronca <dronca@netflix.com> wrote:

> > That's not at all obvious to me. Firstly, why would this be different
> that <tt tts:extent>?
>
> <tt tts:extent> specifies the display area.  A client may ignore the pixel
> address and only use the computed DAR, but that would be a client-specific
> behavior that is undefined in the spec.
>

If the extent is specified, then it cannot be ignored by a compliant
client. A compliant client is obligated to respect that extent
specification.

It is sounding to me like you want to avoid specifying root container
extent at all, but have a way to automatically determine it in the client
based on an a specified aspect ratio and possibly a safe area
specification, is that correct?

If so, would other length specifications always use non-pixel metrics or
percentages? e.g., to specify non-root region origin and extent, use cells
or percentages, but not pixels?