[{"Post":"this is a post","_id":ObjectId("630f3c32c1a580642a9ff4a0"),"iframe":"\"https:/www.youtube.com/embed/RzVvThhjAKw\"","slug":"this-is-a-title","title":"This is a title"}]

db.collection.aggregate([{$set:{iframe:{$first:{"$getField":{"field":"captures","input":{$regexFind:{input:"$iframe",regex:"\"([^\"]+)\""}}}}}}}])