duration: sequence -> (integer, integer)
duration returns the the relative duration of sequence seq as a fraction enum / denom which is represented as the 2-element list (enum, denom). The computation of the duration is solely based on the values of the notes within seq, tempo settings are insignificant.
The empty sequence [ ] has a duration of (0,1).
> duration([c1/4. e/8 f/2])
> duration([_*5/8 _/4..])
> duration([ ])
See also: time, fragm.