This video, via karlocleto, takes a look at how to warp ‘difficult tracks’ that have tempos that drift:

In this second warping tutorial, we take a look at warping an older hip-hop track with drifting tempo throughout the song.

This warping process can be used to warp songs with live drummers, older hip-hop and r&b, disco, soul and other relatively “difficult” kinds of music with beats that aren’t quantized to a fixed grid.

This earlier video looks at basic warping in Ableton Live: