[FFmpeg-devel] [PATCH 18/23] lavc/movtextenc: add alpha tag handling

[Philip Langdale]

On Thu, 9 Apr 2020 16:17:21 +0000
John Stebbins <jstebbins at jetheaddev.com> wrote:

> > > 
> > > Worth a comment that secondary alpha can't be preserved?  
> > 
> > Sure, will do.  
> 
> Taking a second look at this, I'm wondering if alpha_id = 2 should be
> applied to the highlight color that is set in mov_text_color_cb?  And
> if so, should a highlight box be started if only the alpha is changed
> and not the color?  And if so, should the highlight color default to
> the current primary color when only alpha changes? I'm not familiar
> with how mov text highlight works and what it looks like in practice.
> Do you have an opinion?
> 
> If I add the above, I'll do that as a separate new patch, along with
> the comment below.
> 
> There should still be a comment here (and probably for color as well)
> that outline and background colors can not be modified in mov text.

I'm afraid I don't know either. I've not encountered any truly rich
movtext subtitles so I don't know what these things are supposed to
look like. It sounds like a reasonable argument to say you can apply an
alpha-only highlight, but I couldn't even say if that's in-spec or not.
:-)

I agree that handling anything like that can be a separate patch.
 

--phil