MP4 vs MPG

MP4 - MPEG-4 is a container format not a codec. The mpeg-4 standard contains different substandard and one is "mpeg-4 part 2" which is the "first" more simple codec used in .mp4 containers. The MP4 file format defines the storage of MPEG-4 audio, scenes and multimedia content using the ISO Base Media File Format.

MPG - mpeg-1 and mpeg-2 are both different codec (how to compress video) and container formats (how to save video, audio and data together in a e.g filer format).

Summary:
1: MPG is much older than MPEG-4
2: Mpeg-2 is used in digital standard TV broadcasting and also on DVDs.
3: MPEG4 is one of the most popular variants as it found prominent use in mobile devices
4: AVC/h.264 codec in .mp4 container is used for broadcasting high definition TV and requires more CPU power to decode than mpeg-4 part 2 codec.

Other Comparison: MOV vs WMV / 3GP vs 3G2 / MP4 vs FLV / MKV vs MP4 / MP4 vs MP3 / 3GP vs MOV / 3GP vs FLV / M2TS vs MP4

Related Post of MP4 File formats

Related Post of MPG File formats