The best application to add soft subtitles to M4V files.

As easy as open the video file, drag and drop the subtitle file on it, select the language as a reference and save the file. Done.

If the subs doesn't match because they are from other video source, then it's a little bit more tedious, but still easy. You have to adjust them with the controls, save the movie (.mov) and then rename it again to m4v. Works like a charm. I love it.

Now only need an application to extract subtitles from the DVDs and I would be even happier. Unfortunately, I think there is only D-Subtitle, that doesn't work for my spanish subs.