Re: WebVTT Text Positioning

OK, so if I understand correctly, when not using regions, c/s 1.4 is the
relevant section and the implementation will handle font size and line
height.

Thanks,
D


On Wed, Jun 26, 2013 at 7:22 AM, Silvia Pfeiffer
<silviapfeiffer1@gmail.com>wrote:

> On Wed, Jun 26, 2013 at 10:11 AM, Silvia Pfeiffer
> <silviapfeiffer1@gmail.com> wrote:
> > 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)
>
> Actually, I got this wrong (this only applies to the new region spec
> that I just included into the spec).
>
> Without regions, the line height is calculated by the browser from the
> font size. By default, font is set to '5vh sans-serif'. Browsers make
> individual decisions on what the best line height is for that (see
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=19273).
>
>
>
> > 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)
>
> The CEA-608 spec fixes the different line heights that browsers choose to
> be
>   line-height: 5.33vh;
>
>
> > 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
>
> If you change the font size, you should adapt the line-height setting
> accordingly in your application.
>
> HTH,
> Silvia.
>