How to use A-B repeat feature of VLC?

In the View Menu click Advanced Controls. This will display the loop button (A-B) on the bottom.

The previous answer is out of date. I have version 2.1.4 (May 2014), on a Mac.

Press cmd-J to jump to the start of your loop, then cmd-shift-L to mark it.

Press cmd-J to jump to the end of your loop, then cmd-shift-L to mark it.

You can then watch your loop.

Press cmd-shift-L a third time to cancel the loop.

Note that although the dialog for cmd-J says "seconds", you can enter minutes and seconds normally (e.g. 4:34).

I believe this can also be accomplished on the CLI:

--start-time starts the video here; the integer is the number of seconds from the beginning (e.g. 1:30 is written as 90)

--stop-time stops the video here; the integer is the number of seconds from the beginning (e.g. 1:30 is written as 90)

--repeat repeats current item until another item is forced

For example

vlc movie.avi --start-time 240 --stop-time 560 --repeat

Source: https://wiki.videolan.org/Documentation:Command_line/

What I found works is: Tool ---- Customize Interface

Then I added the a-b loop button to my interface.

First Click sets the A Part and the Second sets the B part.

Then you have your loop :D