subtitles: show timed-fragments of the same text line

Question

Note: this is all about editing .ass (or Advanced SSA) subtitles.

I just happen to download Death Note series with chapters in mkv format, and found what seems to be a new subtitling method being used; instead of the usual line after line, it grabs the entire sentence and shows portions of it over-time.

Example of usual method:

N-No! It can't be!

Example of this new method:

N-
N-No!
N-No! It can't be!

The sub is always centered and uses the same space for the end sentence, in all the sequences, therefore N- and N-No! won't center themselves.

Another detail: with MPC player I always force the font into default style (Arial) instead of the one that comes with the mkv file, and it still works perfectly, so apparently this method works with any font besides the one provided.

Does this method have a name so that I can get started learning about it?

Answer 1

After suprisingly open the mkv with Aegisub itself, I found out that to achieve this effect, it uses a tag called alpha (like so:{\alpha&HFF&}) that changes the transparency of the text.

To do this effect, you need to duplicate the same line as many times as you need (no need to cut the original transcription), then use the alpha tag to make the text invisible afterwards, like so:

N-{\alpha&HFF&}No! It can't be!
N-No!{\alpha&HFF&} It can't be!
N-No! It can't be!

To achieve this:

N-
N-No!
N-No! It can't be!

Bear in mind that putting the tag before a comma or a dot could cause some trouble with text positioning (it is supposed to be centered). Instead I recommend use this after the comma or dot.