How to align only subtitles with dialogues to the left, in .ssa format,
while the others remain "centered".

I found the solution, even if I have to manage .ssa subtitles by hand.
My solution is easier done than said.
(Sorry for my english, please)

Tools needed:

- Notepad
- Freeware InfoRapid Search & Replace (or any other tool that use Regular Expressions). A little but useful tool !
- My script for Search & Replace. Please copy following text in a new file in Notepad, and then save to any name, in text format (txt), for example "Dialogues.txt".

1. First create your file .ssa with any subtitle editor. I use Subtitle Workshop and choose my "cosmetics" in menu Settings -> Output settings. Obviously, choose "centered" alignment.
Important 1: subtitle file must be in .ssa format.
Important 2: don't rename the "Default" style.
Important 3: the first character of the subtitle that you want to aligned to left, must begin with the character "-" (hyphen)

1b. Backup your original .ssa file. Then, open your .ssa subtitle in Notepad.

2. Clone the "Default" style, copying the row as in figure 1, straight after it, then press [ENTER]:

2b. Naming the new style with a name to your choice (for example "DialoguesLeft").
So, overwrite word "Default" with "DialoguesLeft" or any other name).

3. Change the thirteenth (13) parameter in new style, from 2 to 1, as in figure:

Then, save your file.

4. Now, you will have to apply new style only to those subtitles with dialogues, which start with a "-" character.
InfoRapid Search & Replace will replace "Default" occurrences with your style "DialoguesLeft" in a flash.

5a. In "Search" tab (1), next to the input field "In Files", press button [...] (2) and choose your .ssa file.

5b. Click on "Replace" tab (1), and click on button [...](2) . Choose the batch file created before ("Dialogues.txt").

6. In "Replace" tab, click on "Start" button, and then in "Confirm Replace" message, check "Replace All" and at last press "Yes" button.

Now your subtitles with dialogues, which begin with "-" character, are aligned on the left.
In this manner, they are similar to commercial DVDs.

Here my new file in MaestroSBT preview:

And here viewing in Media Player:

That's all!