MPEG-4 video file
M4V is a file extension for a container file defined in the systems part of the MPEG-4 standard (ISO 14496-1), as downloaded by iTunes. An M4V file can be renamed to the more common extension of MP4 to be played on other media players if not protected content.
An MP4 file can contain an audio and a video stream in any number of codecs but most commonly uses H.264, also known as MPEG-4 AVC (Advanced Video Coding). MP4 also supports multiple audio streams and video streams, subtitle streams, 2-D, 3-D graphics and advanced interactive content.
H.264 offers significantly greater compression than its predecessors, up to twice the compression of the current MPEG-4 ASP (Advanced Simple Profile), in addition to improvements in perceptual quality. The H.264 standard can provide DVD-quality video at less than 1 Mbps, and is considered promising for full-motion video over wireless, satellite, and ADSL Internet connections.
Learn more about M4V files:
Visit the MPEG webpage.
Andoni Oconchubhair defines MPEG standards at Search SOA.
IT Knowledge Exchange is a good place to search for MPEG-related information.