Similar to how MP3 files work by compressing audio files without affecting the audio's quality, MP4 works the same way, but with video files and with added complexity. The large video files of both motion and audio is compressed into a single and simple file. MP4 is commonly known as MPEG-4 AVC (Advanced Video Coding). This new technology have hopes to decrease the size of the video, which in turns minimizes the risk of running out of space with older computers, making it easier to work with for the users. Like stated before, the MP4 files are compressed into very small files into an extent that quality is not affected in any way.
How the MP4 files manage to retain its quality is by dealing with specific coding situations, reducing certain aspects (such as temporal and spatial redundancies), transforming and changing the motion and intra estimation into the frequency domain, and inputting codec. The MP4 players work in a simple manner as well. Attach the device into the computer, notebook, or TV and start the desired video. The advantage of the MP4 technology is that the video files are played in DVD quality at less than 1 Mbps (through a broadband connection).
With a MP4 player, one can take videos through an Internet connection and watch them immediately in perfect quality. Lower MP versions can be played in the player, such as audio MP3 files. Disadvantages, though not many, exist through the realms of MP4 technology.
Piracy concerns in the MP3s still continue with MP4. Licensing and piracy problems continue and become even greater as long as MP4 gains its popularity. Despite the small size of a MP4 file, it still takes a while to download the file in a broadband connection. In a nut shell, the file is generally still large, even if it is compressed.
Tom Paine writes for The Tech FAQ and is the author of articles such as MP4, Convert MP4 to MP3, and MP4 CODEC.