1. General introduction

1.1 Ways to encode subtitles

There are 2 ways to encode a subtitle:
1. Hard subtitle (a.k.a. burnt in subtitle)
2. Soft subtitle

1.1.1 Hard subtitles

The subtitle is included in the video itself. It’s part of the image. The subtitle is thus permanent and cannot be switched or off.
As hard subtitles are part of the video, they cannot be managed in Subler (or in any other program by the way).

1.1.2 Soft subtitles

The subtitle is in a dedicated stream and not part of the video itself. Thus it can be activated or not depending on the choice of the viewer. It is a more flexible solution but some parametrization is required.

1.2 Types of (soft) subtitles

There are 2 types of (soft) subtitles:
1. Regular subtitles
2. Forced subtitles

1.2.1 Regular subtitles

A regular subtitle can be activated or deactivated depending on the viewer wishes.

1.2.2 Forced subtitles

A forced subtitle will show-up even if the subtitle track is deactivated. It’s useful when a foreign language is spoken during the movie requiring subtitles in order for the viewer to follow the movie in very specific scenes.

Forced subtitles can be handled via 2 ways:
1. Have a dedicated subtitle track containing only the forced subtitles
2. Within the track containing the regular subtitles, mark some of them as forced.

2. Subtitles in Subler

2.1 OCR

When a movie is ripped from disc support and soft subtitles are kept, most of the time, they are not saved in text-based files. They are saved in “VobSub (bitmap)” or “PGS” format. With VobSub and PGS, each subtitle is an image that will be displayed on top of the video.

The problem is that iDevices and QuickTime are not able to read VobSub or PGS subtitles. iDevices and QuickTime requires text-based subtitles files.

Fortunately, Subler offres a great feature: OCR (Optical Character Recognition). Subler will scan the VobSub or PGS subtitle track and transform the images in text.

To improve the OCR quality, download the requires language data files in Subler’s OCR preferences. Without these files quality will be lower (for English language), or result will be unreadable (for non latin languages).

We have first to check that Subler is configured to convert the Bitmap subtitles to Tx3g (specific format of text-based subtitle file):
1. Open Subler
2. Go to the preferences
3. Go to advanced
4. Make sure the option “Convert VobSub to Tx3g” is checked.

Then, to convert VobSub to Tx3g subtitles you can follow the following steps:
1. Open Subler
2. Go to menu ‘file’
3. Create a new file (an empty Subler window opens)
4. Drag and drop your video file in the window
5. As on the picture below, passthru (= keep as it is) every track (if you only want to edit the subtitle) and for the subtitles track(s) make sure that the action Tx3g is selected for the VobSub subtitle track.

6. Go the menu “file” and hit “save as” (to keep the original one as a back-up) and select the directory where you want to save it.

Now you have your subtitle track in a text-based file that you can export in a srt file for edition. It’s advised to do it in order to copy your text in a word processor and run a spelling and grammatical check to fix the OCR errors.

When it’s done, save your file in the same .srt file format (check here for the details) and re-import it by dragging and dropping it in the Subler window. You can delete the previous version of the track in order to only keep the fixed one.

2.2 Subtitle track options

The following options are available for each subtitle track:

2.2.1 Alternate group

An alternate group represents a group of steams. Each stream within the alternate group can be switched with another one of the group.

Typically, each audio track will belong to a same alternate group and all subtitles tracks will belong to another one.

e.g. set all your audio tracks to alternate group 1 and all your subtitles to alternate group 2.

2.2.2 Forced

We have 3 possible values for this option:
1. No : This is a regular subtitle track. When watching the movie, if the subtitles are turned off, no subtitle form this track will show up.
2. Some samples are forced : Forced subtitles are included in this regular subtitle track. If the subtitles are turned off, only the subtitles marked as forced (with the 3 exclamations marks, as described here) will show up.
3. All samples are forced : All subtitles from this track will be considered as forced. If this option is chosen, the subtitle track won’t appear in the subtitle menu of the player (because they will be always displayed) and they will show up automatically. This value is useful if you have a specific track with only the subtitles related to few scenes in a foreign language.

2.2.3 Forced track

Extract from QuickTime File Format Specification (p. 219):

Basically, this should only be used in case timings are differents.

Hint : Don’t link a track to itself. I did it on a track having the option “some samples are forced” and the result was that the forced subtitles did not show up automatically.

So most of the time, this option will have value “none”.

2.3 Audio track options

This option is useful to link your audio track with a forced subtitle track. You can omit this step if the language of the audio track and the forced subtitle track to be used match.

If no forced subtitle track is linked to an audio track (and if the language of the forced subtitles track does not match with the one of this audio track), then the forced subtitles won’t show up automatically when the video is played with this audio track.