MPEG-4 Video File
M4P is a file extension for a protected audio file encoded with advanced audio codec (AAC), which is a lossy compression generally intended as the successor to MP3, which had not been originally designed for audio only but was Layer III in an MPEG 1 or 2 video files.
M4P stands for MPEG 4 Protected (audio). The M4P file extension is seen in an Apple iTunes purchased song which uses Apples “Fairplay” DRM (digital rights management). Unprotected AAC files have an M4A extension.
Both M4P and M4A file extensions are used for audio-only files. Audio-only MPEG 4 container files usually have an M4A file extension.
AAC or M4P file quality is better and file sizes smaller compared to MP3 files. M4A files sound better than MP3 files when encoded at the same bit rate due to some of the enhancements made to the format such as:
- Compression based on perception -- if it is not within human perception, that sound data may be lost without notable effect to quality.
- Smaller sample block size of 120 or 128 samples rather than 192 for changing (or transient) signals, allowing for more precise details where they are needed.
- Larger block sizes in stationary signals, 1024 or 960 vs MP3's 576 sample blocks, allowing for less data to represent a portion of the music that does not have the same complexity.
M4P files can usually only be opened with iTunes and the computer must be authorized prior to playing transferring from an iPod or burning the file. An iTunes account can be authorized on five computers and an iPod may contain the content from a maximum of five accounts.
Learn more about M4P-related files:
Andoni Oconchubhair defines MPEG standards at Search SOA
Look for answers to M4P-related questions on IT Knowledge Exchange.
See the iTunes webpage.
Visit the MPEG webpage.