I happily found this

pet@pet-desktop:~/Desktop/python$ file mit-6-00-f08-lec01_300k.mp4
mit-6-00-f08-lec01_300k.mp4: ISO Media, MPEG v4 system, version 2
pet@pet-desktop:~/Desktop/python$ file ../berckly.flv
../berckly.flv: ISO Media, MPEG v4 system, version 2
pet@pet-desktop:~/Desktop/python$
they are same format, though the video files downloaded form berkeley has, defualtly, no extention