Is there any default tool in OSX by which to add text (such as subtitle) to a video?
iMovie may work for you.

Import your Movie and then.

1,  Select the Titles in the Content library to pick Title theme

2, Drag the Subtitle Theme down to the movie strip.

3, Adjust the Subtitle time line to where you want it and duration.

4, Write you text in the text field.

5, Set your text style.





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