Key Difference: MP3 is short for MPEG-1 Audio Layer 3.  It is a patented encoding format for digital audio. An MP3 file compresses this data using a 128 kbit/s setting that results in a file that is about 1/11 the size of the original data. The MP4 is a container format. This means that it can be used to store audio and/or video data. MP4 files can also be streamed over the internet. 

MP3 and MP4 are two different formats for media files. They might seem related and one may assume that MP4 is the new generation of MP3; however that is not the case. They are two different technologies, with different uses.

MP3 is short for MPEG-1 Audio Layer 3.  It is a patented encoding format for digital audio. It uses a lossy compression algorithm which is designed to reduce the amount of data required to represent the audio recording while still sounding like a faithful reproduction of the original uncompressed audio.

Uncompressed audio files are rather large and take up a lot of space. This is mainly due to the fact that sound is very complex and the translation of it into a digital format can take up a lot of data. An MP3 file compresses this data using a 128 kbit/s setting that results in a file that is about 1/11 the size of the original data. The MP3 file can be created at higher or lower bit rates, with corresponding higher or lower resulting quality.

MP3 has become one of the most commonly used audio formats available and has been the standard for audio files for quite some time. Most digital audio players use the MP3 format as the default standard of digital audio compression for transfer and playback of music.

MP4, on the other hand, is based on Apple’s MOV file type. MPEG-4 Part 12 was developed from the Apple’s MOV file and eventually resulted in MPEG-4 Part 14, which is the MP4 format. The MP4 is a container format. This means that it can be used to store audio and/or video data. MP4 video and audio can also be streamed over the internet. 

As MP4 is a container format, it does not have a standard method of coding the audio or video information. Instead it uses codecs that dictate how the audio or video will be coded. Advanced Audio Coding (AAC) is the most popular codec for compressing audio in MP4 format.

MP3 is an audio compression format that is used to compress and store audio on a computer. Comparatively, MP4 is a container format used to store audio and video files. It can even store subtitles for a video file. As a container, MP4 can save audio and video files that have been compressed in different fashions, including as MP3.

However, due to this MP3 players cannot usually play MP4 files and vice versa. Still, there are now a number of portable players and software options available that can play both, for example, VLC player, Winamp, etc. This is mainly due to the fact that the MP4 format has been steadily increasing in popularity.

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