RE: RE: Re: Re: TTML and aspect ratio

>Now in so much as the root container defines the coordinate system, then I believe the most
>general system is one that aligns top left 0,0 with 0,0 of the underlying media, and X,Y
>with the bottom right of the media. Since X and Y can be any real value, it doesn't really
> matter what value we use so 100%,100% seems adequate. If we then allow negative values and
>values beyond 100, we can address any relative position.

Following this model, if the media is 16:9 but the captions were done using CEA-608 (or another format that uses/assumed a 4:3 presentation), then the captions will not be positioned or spaced properly, as required.  There must be a way for the root container to occupy the full height of the underlying media, but only h*4/3 of the width, and the root container must be horizontally centered.  Further, this must be possible with any well-behaved generic W3C-TT implementation, and thus cannot use absolute coordinates.  I can see no workable way other than being able to specify the presentation Aspect Ratio of the root container.

Forgive my frustration, but I feel that we have made no progress.  If I have not explained our problem sufficiently, then please let me know where/how I can better explain.