The rehearsals and recordings took place at Twickenham Film Studios (2–14 January) and then at Apple (20–31 January), with more than one hundred hours captured on film and the corresponding Nagra tape recorders used for the film's audio track. These Nagra tapes are the source for most, but not all, of the bootlegs from these sessions. In addition to songs that would later be released by the group, the Beatles played hundreds of cover versions and original compositions. However, many of the performances were brief (some lasting less than ten seconds), and many of the original compositions are undeveloped ideas or improvisations that have been described as the audio equivalent of doodling. A sampling of the rehearsals was officially issued as a bonus disc with "Let It Be... Naked".