This International Standard is applicable to magnetic video recording using 12,65 mm (0,5 in) tape cassettes on helical-scan video tape recorders and defines the basic M2 format video cassette system. This standard also specifies two different audio recording modes: 1) common audio mode and 2) pulse code modulation audio mode. PCM audio mode has a limited interchangeability. FM audio recording shown in this standard is optional. The object of this International Standard is to define dimensions and other characteristics of equipment which are necessary to ensure the interchangeability of recorded cassettes. The requirements given relate to 525 line-60 field and 625 line-50 field systems.