There is no sound when playing back MP4 movies on a device compatible with MPEG-4.
Movies recorded in MP4 format do not play back on a device compatible with MPEG-4. (No sound when playing back some contents.)
MP4 movies recorded with the Audio Format set to Linear PCM may not play back properly, even on a device compatible with MPEG-4. Check the specifications in the operating manual or contact the manufacturer of your MPEG-4 device for details. Operation is not guaranteed for all devices available on the market.
If you are using a computer the movie files and audio files recorded with the camcorder can be imported, played back, and edited by downloading and installing MVR Studio.