Hi,
this is a mostly complete answer to my own question. Last week, I wrote:
> mplayer displays subtitles from a .srt file just fine when I watch a
> film, however when I use the 'png' output, the subtitles disappear.
> Is that expected? (why?)
Short answer: It's expected. The 'png' and 'jpeg' output drivers
specifically disable (don't implement) on-screen-display
(osd).
Long answer: In the source tree, there's a directory of '-vo'
drivers, libvo/. Each driver has a function called
'draw_osd()'.
In some drivers, such as vo_x11.c and vo_svga.c, the
function has a non-empty body which draws the subtitles.
Viewing the video with -vo x11 lets me see subtitles.
Hacking vo_x11.c to remove the draw_osd() body makes the
subtitles disappear. Enough evidence for my purposes.
In other drivers, such as vo_png.c and vo_jpeg.c, the
function is empty. So it looks like they were never
intended to show subtitles. Slightly unexpected design
decision, but it looks deliberate.
If this is documented somewhere, then I missed it.
Section 8 ("Video output devices") of the manual doesn't
mention the png video output device at all.
> (Originally, I was trying to 'burn' subtitles into the video stream,
> using
>
> mencoder -sub subtitle.srt -o with_subtitles.avi -oac copy -ovc lavc film.avi
Retrospectively, I realise it's not clear from my first post that the
above mencoder command line actually produces the intended
results. For the record: it doesn't work on older versions of
mencoder, such as 1.0rc2-4.2.4, but it does work on, e.g., MEncoder
SVN-r29857-4.3.4.
Matt
