[FFmpeg-devel] Subtitles for GSoC

[wm4]

On Thu, 10 Mar 2016 18:12:57 +0100
Gerion Entrup <gerion.entrup.ffdev at flump.de> wrote:

> On Dienstag, 8. März 2016 20:42:39 CET Clément Bœsch wrote:
> > On Tue, Mar 08, 2016 at 06:21:12PM +0100, Gerion Entrup wrote:  
> > > Hello,
> > >   
> > 
> > Hi,
> >   
> > > my own ideas seems not to be suitable for GSoC, so I looked again on the ideas page,
> > > because I have high interest to do something for FFmpeg this summer.
> > > 
> > > The project, that I find most interesting, unfortunately is a unmentored one, the subtitle
> > > support. Is someone willing to mentor this?
> > >   
> > 
> > I added this task for previous OPW (and maybe GSoC, can't remember). I'm
> > unfortunately not available for mentoring (too much time, energy and
> > responsibility). Though, I can provide standard help as a developer.
> > 
> > The main issue with this task is that it involves API redesign, which is
> > often not a good idea for a GSoC task.
> > 
> > That said, a bunch of core limitations have been solved in the past so
> > it's starting to be comfortable to work on top of the current stack.
> > 
> > I'm summarizing the current state at the end of this mail, which can be
> > useful for any potential mentor and eventually student.
> >   
> > > On the ideas page the mentioned subtitle for the qualification task is Spruce subtitle. It
> > > seems, it is already supported, so I would try to implement the corepart of usf. I know
> > > it is not widely used, but very powerful with similar features as SSA, if I get it right. Do you
> > > think, that is suitable?
> > >   
> > 
> > Spruce has indeed been added in last OPW as a qualification task. USF is
> > more painful but a basic support could be a potential qualification task
> > indeed. You might be able to figure out something playing with the
> > ff_smil_* functions for the demuxing part.
> > 
> > So basically you would have to:
> > 
> > - an USF demuxer which extracts the timing and text (with its markup) of
> >   every event, and put them into an AVPacket
> > 
> > - introduce an USF codec and write a decoder that will transform the
> >   xml-like markup into ASS markup (see below)  
> I've implement such a demuxer and decoder, based on SAMI (see other mail).
> But XML parsing with the builtin tools is a real pain and hard to extend later.
> 
> If the GSoC project come off, please let me change this and maybe the SAMI code
> into code based on a xmllib. Header parsing should be doable then as well.

Since XML libraries are apparently always broken, bloated, insecure, and
hard to use, that has always been a point of contention. Although it
would be the right approach.