youtube-dl -F www.youtube.com/watch?v=Ao6gQ3VzWbM

format code extension resolution note
140 m4a audio only DASH audio 132k , m4a_dash container, aac @128k (44100Hz), 79.72MiB
171 webm audio only DASH audio 133k , [email protected] (44100Hz), 66.18MiB
141 m4a audio only DASH audio 260k , m4a_dash container, aac @256k (44100Hz), 160.03MiB

avconv -ss 00:40:00 -i in.m4a -vn -c copy -t 2:00:00 out.m4a

To cut from 00:40:00 to the end (2:00:00)