[Matroska-devel] adding a 'forced display' flag?

Moritz Bunkus moritz at bunkus.org
Tue Nov 16 13:00:51 CET 2004


> Well. The force feature should be like in DVDs for subtitles. You have 
> no option to disable some kind of subs.

Hmm, if I'm not mistaken then this is a feature of the "menu" system
etc, not a track feature, or am I wrong?

Anyway, I don't like that (personally I don't like the whole "forced
display" issue at all). This would require players to be able to play
two subtitle tracks at the same time. Otherwise the user wouldn't be
able to switch subtitle tracks at all, and that would be VERY
bad. mplayer and xine can only display one, and I'm not sure about vlc
and gstreamer based ones, but I rather doubt vlc can display more than
one. Ok, this is a technical issue, but I still think that forcing the
user to watch something in a pre-set way is bad. Users like to have a

So what I'm ok with would be that having a "weak forced" flag. "Weak"
because it does allow the selection of other tracks instead of the "weak
forced" one, but if no other is selected, then this one will be shown.

Another thing is that "forced" can not be "enforced" by us. Unlike the
DVD forum we don't hand out "Matroska compatible" stickers and signs, so
we cannot really control how players are implemented -- only ask the
authors that they implement it the way we want it.

> But for subs it makes sense to have it in different languages (ie
> unlike what is done on DVD). So IMO many tracks could have the forced
> flag, depending on what language the user prefers (falling back to the
> "default track" if none is found).

some pseudo code:

sub_track = NULL
if (user_wants_subtitles_in_a_specific_langauge) {
  sub_track = find_first_sub_track(language == wanted_sub_language &&
                                   forced_flag == true)

if (sub_track == NULL) {
  sub_track = find_first_sub_track(forced_flag == true)

if ((sub_track == NULL) and
    user_wants_subtitles_in_a_specific_language) {
  sub_track = find_first_sub_track(langauge == wanted_sub_language)

if ((sub_track == NULL) and user_wants_subtitles) {
  sub_track = find_first_sub_track(default_flag == true)

Something like this? Awfully involved, hard to explain to the ones
creating Matroska files.

All in all I'm against adding a "forced display" flag.

So you others -- what is your opinion? Even a short "I'm for it" or "I'm
against it" would be nice, but if only Steve and I decide about spec
changes then I wouldn't be comfortable with it.


If Darl McBride was in charge, he'd probably make marriage
unconstitutional too, since clearly it de-emphasizes the commercial
nature of normal human interaction, and probably is a major impediment
to the commercial growth of prostitution. - Linus Torvalds

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