How do BD forced subtitles work?

[RobertM]

I'm a bit confused by BD forced subtitles. Sometimes I have to manually sift through subs until I get the right one with the forced dialogue, but sometimes the correct stream plays automatically. Is this because I only keep the ENG subs?

Does it work like this?

- There are many sub streams, say 8.
- 2 of them ENG, streams 1 and 4, while the rest other languages.
- Stream 1 turns on all the ENG subs, stream 4 includes the individual FORCED identifiers.
- I delete all but the ENG subs.
- Now the association is lost because there is no longer an ENG stream in position # 4.
- So I have to manually select stream #2 to get the forced subs to display.

But if the forced ENG subs were in stream #1, then they are still in the #1 position and will play automatically.

Does the default setting of the BD player language enter into this? For instance, if it is set as "english" then does it look for and display the default "ENG" subtitles automatically?

[jdobbs]

If you did what you say, the forced subs will still work. The "forcing" doesn't relate back to the position. It is flagged within that stream. Also, BD-RB doesn't change the order of any of the subs on a full backup. That's necessary in order to work with the original authoring (in which selections can be made via HDMV commands or JAVA). If a stream is removed, it's PID is replaced with the PID of a stream that is kept. So if you, for example, removed a French subtitle -- selecting it would actually be the same as selecting the first in the list of subtitles you didn't delete (in your case, the first English subtitle).

If you delete the stream that has the forced subs... then they are gone. But that's about it. The way it works is that each subtitle (line of text) is represented by graphic image held in a Presentation Graphics Stream (PGS) that can be overlaid on the video. Those graphic images are distributed throughout the M2TS in packets with a time indicating when are supposed to be displayed with a value called a Presentation Time Stamp (PTS). They may also have a Decode Time Stamp (DTS) -- but it isn't always required. Everything in the M2TS is ordered by its DTS/PTS. So as the movie plays along, the stream decoders are pulling audio, video, and PGS streams out and examining all of them. If they are part of what is currently enabled (like a selected PGS) they are included in the A/V output. With a PGS stream, though, there is also a flag in each individual subtitle picture element within its Presentation Composition Segment (PCS) that says whether it is "forced" or not -- if that is on, the graphic is overlaid in the output video, even if it isn't selected. That's a forced subtitle.

The default language of the player does enter into it... I believe the forced sub that meets the default language is displayed (at least when there is more than one). But it's been a while since I read that part of the spec -- so I can't remember the specifics.

[RobertM]

Thanks for your reply, that's great info.

But I guess what I'm wondering is why does the stream which contains the forced elements sometimes display by default, with no intervention on my part, and sometimes I have to turn it on manually with my BD player remote? This is for 'movie-only' rebuilds, the only kind I do.

BTW, does the site seem to be really slow lately?

[jdobbs]

I'm working on this now. I know it used to work. But it's acting weird now. I just did "Zero Dark Thirty" as a movie-only encode, which has a few forced subs when Arabic is spoken, and it isn't working right. I'll have to dig around and find out what's going on.

The site doesn't appear to be running slow for me.

[Ch3vr0n]

he's right though. It is for me aswell too. Often takes upto 10-20 sec for a thread to load and it often requires multiple clicks to get it to open at all. Somethin is definitely sketchy

[jdobbs]

Hmmm.... I wonder why it isn't running slow for me? It's virtually instantaneous. I clicked on this thread and it took no more than 1/2 second to come up.

I'm not sure where it is hosted -- but maybe its closer (fewer hops) to me.

[Rich86]

Thanks for your reply, that's great info.

But I guess what I'm wondering is why does the stream which contains the forced elements sometimes display by default, with no intervention on my part, and sometimes I have to turn it on manually with my BD player remote? This is for 'movie-only' rebuilds, the only kind I do.

BTW, does the site seem to be really slow lately?

I don't know if this applies here - but what the heck . . regarding movie only backups/playback:
I have found that some forced subtitles are imbedded in an existing full subtitle file - and display automatically with subtitles set to "off" as long as you have not disturbed that subtitle track in some way.
But occasionally, I come across a title that has a completely separate subtitle file that contains ONLY the forced subtitles - and you must set that subtitle to be defaulted on when you make your backup. The only way to know is to test with the original, as far as I know (ie. double-check to see if your original defaults a subtitle track "on" even though you have specified no subtitles to be on in your audio/subtitle menu choices setup).

"I just did "Zero Dark Thirty" as a movie-only encode, which has a few forced subs when Arabic is spoken, and it isn't working right."
Where in the movie is this happening? I can test a bit here also to see if I run into the same issue, if you like.

[Chetwood]

With a PGS stream, though, there is also a flag in each individual subtitle picture element within its Presentation Composition Segment (PCS) that says whether it is "forced" or not -- if that is on, the graphic is overlaid in the output video, even if it isn't selected. That's a forced subtitle.
Not exclusively, right? I mean, there are (at least) three methods for forced subs:

1. a separate stream that only has forced subs
2. a separate stream that has only forced subs but is not flagged (subs are turned on by navigational commands)
3. a general stream that has several items which are flagged as forced.

Detecting these automatically seems to be a problem for some tools so one's usually forced (pun intended) to browse/extract the subs first to see which stream is which.

[jdobbs]

Not exclusively, right? I mean, there are (at least) three methods for forced subs:

1. a separate stream that only has forced subs
2. a separate stream that has only forced subs but is not flagged (subs are turned on by navigational commands)
3. a general stream that has several items which are flagged as forced.

Detecting these automatically seems to be a problem for some tools so one's usually forced (pun intended) to browse/extract the subs first to see which stream is which.Sure you could do lots of things any of a number of ways. But:

1. Yes... but it is exactly as I explained. Breaking it into a separate file doesn't change it. Forced is forced. There is, technically, no difference between this and #3. You're just removing the elements that aren't forced.

2. This isn't, by definition, a forced sub. It is simply a subtitle set that has been turned on. How is it different? In this case if you select a different subtitle -- this one isn't displayed. It's not a bad way to do it, especially when you don't want forced subtitles overlapping another language. But when it isn't "forced" to be displayed -- it can't be considered "forced".

3. Exactly as I explained.

So in the end, there is only really only one truly forced subtitle method. The blu-ray standard spells out how forced subtitles work, not me. The standard says to set the flag.

[Chetwood]

Which unfortunately is ignored by a lot of BDs.

[Darksoul71]

Gentlemen,

please excuse if I participate in this discussion ! Both Chetwood and jdobbs you are right !

The biggest issue I see here:
Since many BDs ignore "the only one truly forced subtitle method" as the BD standard might define them, there is currently no reliable way to process BD subtiitles which works 100% all the time other than extract the native sup streams from the BD and verify by hand which one is really forced sub. This being said I have no real clue how to integrate this into BD rebuilder. Forced subs have been a PITA to process in the pure DVD area and at least for the last 50-60 BD I have converted this didn't change much.

I have seen type #2 not that often but sometimes you have #1 and #3 while they must not share the same content (e.g. directors comment in English as audio plus a forced subtitle track with the translation to the current countries language).

I am currently only using MakeMKV to rip the BD, MKVCleaver to extract the raw sup files of my language and examine / convert the forced subs to vobsub files via BDSup2Sub. This is of course different from the way BD Rebuilder works. Some sort of automated preview for selected subs could be helpful.

Cheers,
D$

[Chetwood]

Dude, this is a discussion board so you're absolutely welcome to chime in (and to read this (http://forum.doom9.org/showthread.php?t=167710) as well). And while I think that a preview would be helpful, what's stopping you from manually opening the largest m2ts in VLC and cycle through the streams to find the one that is forced? There's no need to extract them cause the stream order will stay the same so you know what tracks to (un)check when ripping.

[Darksoul71]

Cheetwod,

the problem(s) stay the same:
1) I do not know if a movie has forced subtitles unless I already have watched it or found it on some of the many lists in the www
2) Even if I know that a movie has forced subtitles, I must know the exact postions where forced subs kick in to find the correct stream :)

Funny how problems remain even with a new media type :cool:

[Mark_Venture]

I'm a little lost... but I'm guessing... Godzilla (1998 w/Matthew Broderick), and The Da Vinci Code (2006 w/Tom Hanks) has forced subtitles of the kind... "a general stream that has several items which are flagged as forced."... since the subtitles (PGS) that get extracted as .SUP when using HD-DVD/Blu-ray Stream Extractor (see https://code.google.com/p/hdbrstreamextractor/ ) is the entire movie, not just the "forced" subtitles.

Of the PGS encoded into the MKV when I do "Alt Movie Only" backups, none are marked "forced = yes" and when I play it back in VLC Player, none of the subtiles are the "forced only"

If I'm reading this thread correctly, what I'm seeing is expected behavior when using BD-Rebuilder to back up to alt-movie only MKV file?

[Rich86]

Forced Subtitles:
Forced Subtitles still do not seem to work correctly. "Dead Man Down" blu-ray - making a movie only blu-ray from the source.
The forced subtitles work fine in the original with subtitles set to off. There are 48 forced subtitle entries in 2 of the 4 english .sup files.
I included all 4 english subtitles when creating the movie only blu-ray with version 44.15 of BDRB. But the forced subtitles do not work.
Check for this around the 13 minute mark when she is looking out the window waving to Colin Farrell, then has a conversation in french with her mother.
Is there a setting I am missing for this?

[jdobbs]

Please observe rule #8. You posted this exact message in the bug thread.

[Rich86]

Please observe rule #8. You posted this exact message in the bug thread.

Yes - sorry - posted there and then remembered there was a dedicated thread for the topic from a while ago and went looking for it . . .

[jdobbs]

Yes - sorry - posted there and then remembered there was a dedicated thread for the topic from a while ago and went looking for it . . .Anyway, I'll work on a routine that will (for movie-only):

1. Scan the SUP files for forced subtitles.
2. Extract the forced subtitles into a separate stream.
3. Create a new SUP file.
4. Turn that subtitle stream on by default.

Whether I implement permanently as a part of BD-RB will depend on how much time the scan adds to the process and whether I can find any other reason why the existing flagged subtitles aren't being forced.

[Ch3vr0n]

i can't help but think why on movie-only, shouldn't they work for full backup too. afaik for the moment they don't either

[Rich86]

Anyway, I'll work on a routine that will (for movie-only):

1. Scan the SUP files for forced subtitles.
2. Extract the forced subtitles into a separate stream.
3. Create a new SUP file.
4. Turn that subtitle stream on by default.

Whether I implement permanently as a part of BD-RB will depend on how much time the scan adds to the process and whether I can find any other reason why the existing flagged subtitles aren't being forced.

If there is anything I can do to help working with the "Dead Man Down" title, just let me know.

btw - just for info in case it is helpful - I ran it through Clown-BD (v .81) and the forced subtitles work on the output. Clown-BD expanded the 4 english subtitles into 6 (note that 2 of the original 4 english .sup files included the forced subtitles). The output does not have any of the subtitles ON by default, but the forced subtitles are working. I expect I can run this through BDRB to shrink it down to fit on a 25gb BD-R.

[Ch3vr0n]

Perhaps jdobbs should contact the clown_bd author. Obviously he does it a little different to detect and enable forced subs than bdrb does.

[Rich86]

Anyway, I'll work on a routine that will (for movie-only):

1. Scan the SUP files for forced subtitles.
2. Extract the forced subtitles into a separate stream.
3. Create a new SUP file.
4. Turn that subtitle stream on by default.

Whether I implement permanently as a part of BD-RB will depend on how much time the scan adds to the process and whether I can find any other reason why the existing flagged subtitles aren't being forced.

Will this make forced subtitles work on DVD output also? That would be nice.

Also pls note - the same problem occurs with the "Olympus Has Fallen" BD title - forced subtitles do not work after processing with BD-RB in movie only mode.