See the new demo/mlt_slideshow2 to see how easy it was to create that (requires a very recent change to the luma filter that will appear in the next release - v0.5.8):
melt \ photos/.all.jpg ttl=75 \ -attach crop center=1 \ -attach affine transition.cycle=225 transition.geometry="0=0,0:100%x100%;74=-100,-100:120%x120%;75=-60,-60:110%x110%;149=0:0:110%x110%;150=0,-60:110%x110%;224=-60,0:110%x110%" \ -filter luma cycle=75 duration=25 \ -track demo/music1.ogg \ -transition mix
That rather complex looking transition.geometry string is just something I whipped together to add some variety to the animated pan and zooms. A front end tool could contain a collection of these strings to let the author choose a style. Also, notice the addition of automatic center cropping to remove black bars and fill the output frame with the photo image regardless its resolution and aspect ratio.