how is mp4 better than mp3?

Answer 1

With the new players coming on market, the mp3 is basically playing your music or audio files on your player. Now the new players on market that can play mp4, will now play the audio file and you can see the video part too. Just like TV when you watch music videos, now with mp4 you can have portable music videos to watch. Course if you want to watch on a small screen, go for it.

WIKIPEDIA DEFINITIONS
MPEG 1 Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding and lossy compression format and algorithm, designed to greatly reduce the amount of data required to represent audio, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners. It was invented by a team of German engineers who worked in the framework of the EUREKA 147 DAB digital radio research program, and it became an ISO/IEC standard in 1991.

MPEG-4 Part 14, formally, ISO/IEC 14496-14:2003, 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 also can be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. The official filename extension for MPEG-4 Part 14 files is .mp4, thus the container format is often referred to simply as MP4. Devices that play .mp4 files are referred to as MP4 players.

Answer 2

You can't really compare them. MP3 is just Mpeg 2 Layer 3 audio. MP4 is a container that can hold just about any format of audio or video.