[{"channel":"a","video":[{"name":1,"status":""},{"name":2,"status":"err"},{"name":3,"status":"err"}]},{"channel":"b","video":[{"name":4,"status":"err"},{"name":5,"status":"err"},{"name":6,"status":""}]}]

db.collection.aggregate([{"$set":{"video":{"$filter":{"input":"$video","as":"v","cond":{"$eq":["$$v.status","err"]}}}}}])