1. Definition MP3 Player/MP3/MP4/MP4 player
MP3 Player vs MP3
MP3 Player ——A portable consumer electronic device that allows you to store and plays music files in MP3 format. MP3 players are small handheld devices and often use flash memory for storing MP3 files. While frequently called an MP3 player, it fits under the broader category of digital audio players and often an MP3 players can use other file types such as Windows Media Audio (WMA).
MP3——The name of the file extension and also the name of the type of file for MPEG, audio layer 3. Layer 3 is one of three coding schemes (layer 1, layer 2 and layer 3) for the compression of audio signals.

MP4 player vs MP4
MP4 player is a marketing term for portable media players that comply with certain standards and formats
MP4 is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital audio and digital video streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images.

MP3 Player vs MP4 Player
MP3 Player—— A digital audio player
MP4 Player——often called Digital Media Players. This term has evolved for the next generation and uses the versatile Mpeg-4 files for video and audio. MP4 players can store and play music files but can also download video clips, photos and even used as additional and portable storage for your PC data.

2. Popular MP3/MP4 Player Brands in USA
Creative——Creative Zen
Ministry of Sound——MSHK
Sweex Essentials——Sweex Essentials

3.Useful tools for MP3/MP4 Player
Video Converter
DVD Ripper
Video to Audio Converter

4. Top MP3 Searches

5. Mp3 Memory and Storage
The small memory flash players typically have up to 1 GB of memory and store anything from 100 – 200 songs. With the hard disk models 40 GB was the upper limit but now it comes to 80GB or 160GB. As a rule of thumb 10 GB delivers around 2500 songs.

6. Useful Sites
Practical Guides: How To...