Linux Video Stream Processing Tool - Examples
Keywords: DVD, digital video, DV, encoder, divx, DivX;-), lame, source, posix, avifile, opendivx, codec, linux, AC3, program stream, video, audio, transcode, decoder, stream, YV12

Subtitles:
This chapter gives a short introduction on handling and processing subtitles with transcode and related programs. DVD subtitle overlay mode with -J extsub generating subtitle files with subrip adding custom subtitles with -J subtitler

DVD subtitle overlay mode
transcode provides a filter plugin filter_extsub.so for elementary DVD subtitle rendering in connection with -x vob. Use it with
transcode [...] -J extsub=<options>
The option string looks as follows (all options default to 0):
s:h:t:f:w:a:b:p:q
- s subtitle track id (0-31) Use tcprobe -H N with N>1 to find out if subtitle any packs are available in the program stream. h offset of subtitle with respect to bottom of frame in rows. Subtitles are placed at the bottom of the frame. Try this option to shift them up or down. t global display start time correction in msec. If you feel, subtitles are displayed not timely, adjust it with this option. This will affect all subtitles. f fast rendering, i.e., no anti-aliasing (0=off,1=on). Anti-aliasing of the font is performed by default. Switch it of (1) if your font is tiny and messed up by this feature. w render on post-processing (0=off, 1=on). Setting this option to 1 will render the subtitle on post-processing instead of pre-processing. This may improve subtitle quality but makes no sense after extensive resizing of the frame. a graylevel value a (0-255). b graylevel value b (0-255). Make another subtitle color visible with full intensity equal to 255. May lead to fatter fonts. p assign subtitle color p [0-3] to graylevel value a. q assign subtitle color q [0-3] to graylevel value b. Shuffle the color assignment by choosing another subtitle color between 0 and 3. Useful for black fonts on white background. Example (1) changing color assignment:
  -J extsub
- this one looks not as expected without any further options.
  -J extsub=0:0:0:0:0:0:0:1:2
- shuffle the font color assignment using 1:2 looks like this, but has an ugly 3D effect.
  -J extsub=0:0:0:0:0:0:0:1:3
- shuffle the color assignment using 1:3 looks better, but shows white shadows that make the font fatter but blurry
  -J extsub=0:0:0:0:0:0:0:2:3
- shuffle the color assignment using 2:3 seems to be perfect. Nice and smooth looking letters.
  -J extsub=0:0:0:1:0:0:0:2:3
- for comparison, we switch off anti-aliasing, see the difference? Example (2) adding another white color:
  -J extsub
- this one looks already perfect without any options.
  -J extsub=0:0:0:1
- same as above with-out ant-aliasing.
  -J extsub=0:0:0:0:0:0:255
- We make switch another color to full intensity (white) to make the subtitle appear fatter, maybe too much.
  -J extsub=0:0:0:1:0:0:255
The above fat one without anti-aliasing.

generating subtitle files
Please find some documentation on Arne Driescher's subrip program in the `contrib/subrip/` directory or visit the project page for more information.

generating custom subtitles
Please find some documentation on Jan Panteltje's subtitler plugin in the `filter/subtitler/` directory or visit the project page for more information.

Last modified: Thu May 16 12:52:34 CEST 2002