SELECT avg(T1.duration) FROM files AS T1 JOIN song AS T2 ON T1.f_id  =  T2.f_id WHERE T1.formats  =  "mp3" AND T2.resolution   <  800
What is the average song duration for the songs that are in mp3 format and whose resolution below 800?
SELECT avg ( T1.duration ) FROM files AS T1 JOIN song AS T2 ON T1.f_id = T2.f_id WHERE T1.formats = `` mp3 '' AND T2.resolution < 800
select avg ( t1 . duration ) from files as t1 join song as t2 on t1 . f_id = t2 . f_id where t1 . formats = value and t2 . resolution < value
What is the average song duration for the songs that are in mp3 format and whose resolution below 800 ?