MP4 player

The name MP4 player is a marketing term for inexpensive portable media players, usually from little known or generic device manufacturers. The name itself is a misnomer, since most MP4 players through 2007 were incompatible with the MPEG-4 Part 14 or the .mp4 container format. Instead, the term refers to their ability to play more file types than just MP3. In this sense, in some markets like Brazil, any new function added to a given media player is followed by an increase in the number, for example an MP5 or MP12 Player, despite there being no corresponding MPEG-5 standard (as of 2015^[update], the current standard, still being developed, is MPEG-4).

The Archos Jukebox Multimedia was the first commercial portable media player, and was the first to be coined as an MP4 player is a mp4 video.

Today's MP4 Players can play video in a multitude of video formats without the need to pre-convert them or downsize them prior to playing them. Some MP4 Players possess USB ports in order for the users to connect it to a PC. Some models also have memory cards to expand the memory of the player instead of storing files in the built-in memory.

Chipsets and file formats that are particular to this kind of portable media player.

Anyka is a chip that's used by many MP4 Players. It supports the same formats as Rockchip.

Fuzhou Rockchip Electronics's video processing Rockchip has been incorporated into many MP4 players, supporting AVI with no B frames in MPEG-4 Part 2 (not Part 14), while MP2 audio compression is used. The clip must be padded out, if necessary, to fit the resolution of the display. Any slight deviation from the supported format results in a Format Not Supported error message.

...
Wikipedia