There is a significant different between the compression rates of these two formats. MPEG-2 compresses files anywhere between 3.5Mbps and 6Mbps. If the files are compressed at a lower rate, you may find artifacts on the video, especially during the fast-paced scenes. However, the human eye fails to detect them if compressed at 6Mbps.
MPEG-4, on the other hand, has an entirely different compression rate. The rate may vary wildly sometimes. It could be as low as 5Kbps or as high as 10Mbps.
It is not possible to determine exact bitrates, as they vary with each file. However, we can take an average value for both containers.
As far as MPEG-2 is concerned, it offers an average audio bitrate of 448kbps. If the quality of the files is low, the average bitrate will be around 224kbps. This container handles the video at any rate between 5000kbps and 20Mbps. Again, the value depends entirely on the quality of the file.
MPEG-4 offers different bitrates. Its audio bitrate value is 128kbps, whereas it handles video at around 1000kbps.
As far as the file size is concerned, MPEG-4 is nowhere near MPEG-4. A MPEG-4 video file can range between three to 20MB per minute, depending how good quality it has.
On the other hand, MPEG-2 has no fixed values. A DVD-quality file can go between 30 to 70MB per minute. And if the quality is even better, you may find one-minute video file of 150 MBs.
MPEG-2 is usually used for making DVDs and digital broadcasts. This container can even be used for SVCD (Super Video CD) and HDDVDs.
On the contrary, MPEG-4 is used only for MP4 videos. These videos are usually very poor in quality, and can be run by most media players and mobile devices.