Re: [Bino-list] SubTitles?

[Joe]

On Monday 14 March 2011 22:00:06 Martin Lambers wrote:
> Hello Joe!
> 
> On 14/03/11 04:31, Joe wrote:
> >> Some subtitle formats are stored in text form, while others are stored
> >> in a fixed bitmap form. I don't know how FFmpeg handles these two, but
> >> bitmaps could be put into a texture and overlayed onto the
> >> color-corrected video texture, and text could be rendered with an
> >> OpenGL
> >> font rendering library. I'd rather not use Qt's built-in text
> >> rendering
> >> for this, so that we can make subtitles work also with Equalizer. FTGL
> >> seems to be widely used:
> >> <http://sourceforge.net/apps/mediawiki/ftgl/index.php?title=Main_Page>
> >> .
> > 
> > Thanks for the tip! I used FTGL to implement basic subtitles support
> > ("--with- ftgl" configure param). Please see the attached patch (it is
> > one big patch, but I have finer grained history in my repository). So
> > far I've implemented support for srt files and subtitles embedded in
> > video files in form of plain text (tested on Matroska). Subtitles in
> > image form will hopefully follow.
> > 
> > I draw directly into framebuffer, because I'm not so skilled in opengl
> > so I did not managed to put text directly into left/right textures and
> > also was unable to set proper color. I think it would be much better to
> > have it in textures to be able to set "depth" of subtitles. It would be
> > great if you find the time to correct it. (I think FTTextureFont or
> > FTBufferFont will have to be used). Font rendering starts at line 905
> > in video_output.cpp.
> > 
> > The patch is just RFC and I plan to clean it into mergeable state so
> > comment please!
> 
> Thank you very much for your work! It's great that you are working on this.
> 
> I currently only have one DVD video file that has subtitles, and that
> does not seem to work yet - it crashes after a while, without actually
> displaying subtitles. So I did not yet test the rendering code itself.
> 
> Do you have links to some freely available video file samples with
> subtitles, for testing?

DVD uses image subtitles and they are not implemented yet.

I think http://samples.mplayerhq.hu is good collection. I'm testing on real 
movies but I found now this example of embedded multiple subtitles in mkv and 
it surprisingly works :-) 
http://samples.mplayerhq.hu/Matroska/subtitles/multiple_sub_sample.mkv

For testing of srt support, use another example: 
http://samples.mplayerhq.hu/sub/thief.avi and subtitles 
http://samples.mplayerhq.hu/sub/thief.srt . It is working now in latest 
version of my the patch.

The loading and delivery of subtitle into rendering should work, the problem 
is rendering. On my ATI graphic card it is white and in the middle. On my 
Nvidia card, it catches color from video (hard to see) and are not centered. I 
think it will correct once FTTextureFont will be used.

> 
> I have some comments based on a first reading of your patch:
> 
> - It is ok to make FTGL a mandatory requirement, so you can remove the
> --with-ftgl option.

Ok, I realized, that even on my minimalistic system is ftgl installed because 
of some other apps. So it should be an easy dependency (same with Pango).

> 
> - The Debian package of FTGL is libftgl-dev; maybe you can add that hint
> to the configure script for consistency.

Not sure what you mean. Configure has some connection to Debian packages? :-) 
I'm not Debian user so maybe you could change that.

> - From the FFmpeg headers, it seems that SUBTITLE_* should be used to
> determine the subtitle type, not CODEC_ID_*

Yes you are right, I have not noticed such defines exists in FFmpeg. Will use 
them.

> - What character encoding do the FFmpeg subtitle streams use? We may
> need to do a character set conversion and set an appropriate FTGL
> charmap, to get non-ASCII languages right.

FTGL/Pango supports ft_encoding_unicode/unicode. So I would put a combobox in 
configuration dialog with selection of input encoding, than it is possible to 
do the conversion to unicode. Should I use iconv or QT?

> - From the FTGL overview, it seems that the Texture font type might be a
> better choice than the Bitmap font type, because it has antialiasing
> support?

I'm using Bitmap/Pixmap  because it was the only font I was able to get text 
on screen. Please, help me to get FTGL/Pango render into left/right textures 
with FTTextureFont/buffer with Pango rendered font. I'm not Opengl guru as you, 
so I've tried but always end up with corrupted image.

> - Is there a way to use font names instead of specifying font files?
> Then, the default could just be "Sans" to get the default sans serif
> font of the system. Arial.ttf is problematic because it is not strictly
> free and thus not available by default on all installations. Maybe we
> need to use fontconfig to translate a font name to a font file.

Yes I hate to set font file instead of "logical font name", but it was the only 
way, because QT did not offered me the way to get absolute font path from 
QTfont. Maybe it would require some more low-level X library to get that path, 
but it will break windows versions.

> - Or maybe we should use something more modern than FTGL; maybe Pango?
> Then we could use the system's default font choosing mechanism. But we
> would have to render the subtitle into a memory buffer and then upload
> that as a texture so that we can render it. Opinions?

Yes, Pango could be even better replacement of FTGL, because we don't need to 
draw in 3D. I will look at that.

> - Some minor style inconsistencies: please use spaces instead of tabs,
> and avoid spaces at line ends. Also, there are some places where spaces
> are missing spaces after if/for/...

Did noticed the spaces. I'm not used to them but will follow.

> 
> It would great to merge your work. How should we proceed? Would you like
> to post updated versions of the patch, or should we set up a 'subtitles'
> branch in the Bino repository that we can later merge into the master
> branch?

I've set up repository on GitHub: 
https://github.com/cuchac/bino

I will do all the development there and you can pull from it when you think it 
is ready/usable enough. Few minuted ago I pushed one little fix to be able to 
play Thief.avi example for srt testing.

> Best regards,
> Martin

Joe