I listened twice. They did say 8000 meters. I was surprised by that too, since I assumed the flight would be higher.
Here's a bit more of an exact translation: "Taking off in full night, the flight was flying at 8000 meters when it demanded a change of heading 20 minutes after take off. "The aircraft" [I can't quite make out the word used - it almost sounds like they say "the wings"] then fell suddenly to 4 millimeters [yes! that's really what it says] before disappearing from the screen."
Note: This is the radar image from the Ouagadougou control tower.
Note: I'm very sure about the 8000 meters ("huit mille metres") and the 20 minutes after take off ("vingt minutes apres decollage") - both facts which surprised me somewhat. The key section is from 11:20 - 11:35 of the video if anyone else wants to give this a listen to double check what is said.