If you legally own the episode (e.g., purchased from iTunes), the file will likely be (video) or MP4 . To convert or play on different devices:

Meet 9-year-old Sheldon Cooper as he skips four grades to start high school alongside his less intellectually endowed older brother. While Sheldon struggles to fit in with his family and peers in East Texas, we get the first glimpse of the genius mind we grew to love in The Big Bang Theory .

M4P is an – a protected AAC file (typically purchased from the now-defunct iTunes Store with DRM copy protection). It is not a video format for TV episodes.