Re: WebVTT Text Positioning

On Wed, Jun 26, 2013 at 12:53 AM, David Ronca <dronca@netflix.com> wrote:
>> Is the conversion spec not clear enough on this?
>
> Not really.  Trying to reconcile what you had previously said, "Line height
> is set by CSS automatically based on font size".
>
> with c/s 1.4:
>
> The line height is defined as 5.33% of the video height, because CEA-608
> requires 15 character rows to be rendered on 80% of the video rendering
> area’s height.
> The font size is defined from the line height by dividing it by 1.3; this is
> to make sure there is enough space for the characters in a line.
>
>
> and c/s 1.5:
>
> The actual height and width of the caption window depends, however, on the
> actual font size.
>
>
> So, according to 1.4, font size is line height /1.3, and line height is
> defined as 5.33% of video.  This makes sense, and suggests that the renderer
> will select the appropriate line height and font size based on video window
> size.  However, your comment and 1.5 seem to suggest the inverse, that the
> dimensions depend on font size.
>
> Is there is an obvious point that I am missing?

So, the way I'd look at it is:

1. Line height is set to 0.0533vh by the WebVTT spec (hmm..  I think
this should be 5.33vh actually, looking at the CSS spec)
2. You override this with CSS for CEA-608 if necessary (in this case,
it probably isn't because becase 5.33vh is exactly what you want)
3. You can now also change the font size in the application (e.g. if
older people want to increase the font size) - then the line height
should be changed accordingly

Does that help?

Silvia.

Received on Wednesday, 26 June 2013 14:12:45 UTC