MP4 is the short name for a special video format called MPEG-4. The format can compress large video content into a relatively small document while keeping its quality.

　　They named it MP4 mainly because it was regarded as an update from MP3. MP3 only compresses audio documents.

　　After MP3 players became popular, some technology companies started thinking about making videos that fit into people's pockets. In fact; most PDAs and some hand-held mobile phones already have video function.

　　Since then, manufacturers worldwide have joined in the rush. Among them are big companies like Sony, Microsoft and Apple, although they don't call their products MP4 players.

　　Sony called its product with video function the PMP (Portable Media Player). Microsoft prefers PMC (Personal Media Centre), while some others call the gadgets PVPs (Personal Video Player).

　　But, basically, these products all have the same core function--playing video content.

　　An MP4 player is not just an MP3 player with an extra video function.

　　In fact, MP4 players must be able to play, record, and transform large video content. That requires an overall change in both hardware and software. Storage must be enlarged, display strengthened, speakers powered, software upgraded, and appearance redesigned.

　　Since video function enriched the players, other functions such as games, cameras can be added. Sony's PSP (Play Station Portable) was originally built for video games.

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