Sadly, this feature doesn't work good for me. I tried it with SMPlayer rev 3403 (pre built) and with rev 3423 (built by MuldeR) and a rev built by myself without any changes.
Every time I set the two markers, the video begins to loop, but it fails, escpecially when the markers are near by each other. Then the Video jumps to the beginning and erases the markers/deactivates the loop. Also when I jump through the timeline while a sequence gets repeated the loop is aborting. It only works (sometimes!), when I set the markers in a very big difference, and when I don't touch anything while it's repeating.
Is this feature expereminental (it seems you've added it only 2 or 3 month ago), or will the AB-repeat stay that messy because of some limits by mplayer? (In "The KMPlayer" AB-repeat works very well, but I would prefer SMPlayer when this feature would work).
By the way, it would be really nice when you would show the markers in the timeline
