If you are a heavy twitter use, possibly with more then one account, than I suggest you to give Tweetdeck a try. You can arrange, schedule, monitor and manage your tweets with ease.
If any file can not be deleted, then you can use the program LockHunter, which removes the active connections of other applications to that file, which allow you to change or delete file.
If you want to put your video files online using HTML5 then it's recommended to have three different formats for a full browser support. Those formats are mp4, ogv and webm.
