default and forced track flags for matroska subtitles

[Chetwood]

Originally Posted by TypX

To fix bug we first have to know them

Right, but don't you guys have a common pool of various testfiles (different containers, audio, subtitle streams) that are tested against each new build?

Originally Posted by TypX

I agree, a player shouldn't and surely won't bypass user preferences because the people that made the file wanted it.

Except for forced subtitles of course. No matter what the player is set to, forced subs should be displayed. The WDTV does NOT do this, thus when watching Avatar or District 9, you need to switch on the stream when your device is set to off usually.

[TypX]

Originally Posted by Chetwood

Right, but don't you guys have a common pool of various testfiles (different containers, audio, subtitle streams) that are tested against each new build?

In a world were we have enough people to make these files and people to test it. It's very difficult to do with just 6 or 7 people active. If some people want to do that to help, they are more than welcome. Personnaly when I commit I run basic to test that I didn't break everything but apart from playing samples that I dl during my debug tests, seeking. I don't have 10 hours to spend to test everything each time I commit.

Originally Posted by Chetwood

Except for forced subtitles of course. No matter what the player is set to, forced subs should be displayed. The WDTV does NOT do this, thus when watching Avatar or District 9, you need to switch on the stream when your device is set to off usually.

Well now it should display forced only subs if you didn't ask in your preferences that you don't want subtitles. Now different default and forced tracks won't work without modifying core, since, once again, most players I know are designed to play only one track of each type.

[Chetwood]

I don't want subtitles and set my player accordingly. However, since I don't speak, Navi, Elvish or Klingon, the player should ALWAYS display a forced sub, no matter what. If the player can't display 2 sub streams at once, the it should default to the forced sub.

[mindbomb]

Originally Posted by Chetwood

I don't want subtitles and set my player accordingly. However, since I don't speak, Navi, Elvish or Klingon, the player should ALWAYS display a forced sub, no matter what. If the player can't display 2 sub streams at once, the it should default to the forced sub.

i randomly started thinking about this again. even though these are the classical examples of when to use the forced track flag, the ones with the language that no one could possibly understand, a player that was strictly following the specs would show this under all circumstances. However, what if the user then manually selects a subtitle track like mandarin chinese? Then the english and mandarin would be shown together?

So even in an extreme case like this, it seems like you would be safer just marking it as default.

[Chetwood]

Which only goes to show that not all usecases have been properly thought through when coming up with the specs.

[Chetwood]

Originally Posted by Mosu

Citing the specs for "forced": Two things to note here:

1. "must be active during playback". Not at the start of it, but during. The whole time.
2. The specs mention explicitly that a forced and a non-forced track of the same kind can be played at the same time.

Yes, our intention had indeed been that players would have to display more than just one subtitle track at the same time in certain situations.

So what would be the proper behaviour with two forced tracks (English and German) flagged as such? The player has to ignore language preference due to rule 1 and display both simultaneously?

[sneaker_ger]

The player has to select one of them, either via language preference or the one that has an additional default flag.

[Mosu]

The languages of the forced tracks are supposed to be taken into account. If you're generally showing German subtitles then all subtitle tracks that are both forced and German should be played as well. If you have exactly two forced tracks with different languages then only one of them should be shown. And if you're generally showing French subs then neither the German forced nor the English forced should be shown.

So in this particular case the player should chose at most one.

[Chetwood]

And what about tracks that are missing the default flag entirely? Apparently MakeMKV produces them occasionally and VLC e.g. plays such a track automatically as if it were forced.

[Mosu]

Read this fine FAQ entry.

[Chetwood]

Thanks, that explains why VLC acts as it does though not necessarily why a missing flag would ever be translated to 'yes' rather than 'no' (I already mentioned that I find the specs to be a little odd in regards to flagging).

[sneaker_ger]

Why? Because the specs say so - as simple as that. You can find default values in the 7th column:
http://www.matroska.org/technical/specs/index.html
The default value for "FlagDefault" is "1" according to the table.
http://www.matroska.org/technical/sp...Default_Values

There really isn't more to it than what is already written in the FAQ.

[Chetwood]

Originally Posted by sneaker_ger

Why? Because the specs say so -

Really? You don't say!

Originally Posted by sneaker_ger

There really isn't more to it than what is already written in the FAQ.

Actually there is: silence does not mean consent. But since Mosu already said how much effort there is in getting the specs changed, I won't be walking the extra mile.

[sneaker_ger]

Your proposed spec change would be a total reversal of the current spec, in turn braking many many existing files without written default elements. Of course chances of getting that through are extremely slim. I agree that it was a questionable design decision in the first place (probably made to maximize saved space by always using the most common value) but it's not nearly enough to justify a reverse, it would be insane. Also, players that do actually make use of the elements like flagdefault and language seem to handle them correctly in general so I don't see any need for a spec change. Any spec change should serve a purpose to justify itself and I don't really see that in this case.

[nevcairiel]

I don't see why it even matters. It would only be a problem with broken muxers that don't write the element at all, otherwise the muxer should just let you decide if its default or not, and then the muxer decides if it actually needs to write the element or not.

[Chetwood]

Exactly, MakeMKV seems to be broken in that regard but I'm sure Mike will take care of this sooner or later. I'm just pointing that the current default approach - while generally a good idea (albeit not saving that much space in the first place) - does not necessarily make sense for each and every item of the spec.

[nevcairiel]

MakeMKV seems fine here.
I ripped many BDs with 2 audio tracks, and only the first is recognized as default, which means the second must have an explicit "no" flag.

Does it just fail on this for subtitles? I usually dont mux any of them, tbh.

[Chetwood]

It's all explained in the link to the MakeMKV forums. So far I had only one BD where the flags were missing.