Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE files (duration INTEGER, f_id VARCHAR, formats VARCHAR); CREATE TABLE song (f_id VARCHAR, resolution VARCHAR)
### Question:
What is the average duration of songs that have mp3 format and resolution below 800?
### Answer:
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