[{"t":"Sample Question","d":"2018-12-23T21:21:03.430Z","aa":[{"q":1,"n":"5bee73accda38","iU":"5bee73accda38/5c1f3d7341977/1.mp4"},{"q":4,"n":"5bee73accda38","iU":"5bee73accda38/5c1f3d7341977/1.mp4"}]}]

db.collection.aggregate([{$unwind:"$aa"},{$sort:{"aa.q":-1}},{$group:{_id:"$_id","t":{$first:"$t"},"d":{$first:"$d"},"aa":{$push:"$aa"}}}])