Originally posted by Jane_Lane
I was thinking mpg is baically the same as mpeg and since mpeg is more or less the format for VCD
Which is true. A VideoCD uses the MPEG standard.
Brief explanation about what the hell Mpeg is
The Moving Pictures Experts Group have made this standard ( = ruleset = protocol ).
The (very very very) basic explanation is , that the protocol compresses images. (All movies are in basic a lot of images with sound). With MPEG , you can choose various gradations of compression. There are two kinds of compressions :
1 : Lossless compression ; Compression without quality loss when compared to the original.
2 : Lossy compression ; Compression WITH quality loss.
In the case of MPEG , they’ve come up with a very smart kind of compression.
Imagine you have this movie about a car moving on a road and want to compress this with the MPEG standard. This basically is what MPEG does :
a) It takes a look at the very first frame and keeps it that way. It uses this frame as a reference.
b) It takes a look at the second frame , compares it with the first frame and only saves that part of the image that CHANGES.
Say for instance that the first frame shows a road without the car and the second frame shows the road with a car on it. The first frame stays intact , but to show the second frame , you just need to “add” the car to frame 1. This saves an enormous amount of image data (around 90%). If lossy compression is used , you can even save up to 99% of data. (This is called motion prediction)
If you would like the exact details and lots of technical mumbo jumbo about it , then check here.
The VideoCD standard
A Video CD is a kind of CD. It looks the same as a music CD or a CD-ROM, except that instead of music or software, it holds movies, using compressed MPEG-1 video. Its resolution is 352x240 (NTSC) or 352x288 (PAL), which is roughly comparable to VHS.
More information can be found here.
Why the bloody amount of disk space ?
If you have a movie from a different format than above , some program must decompress and recompress the movie into the MPEG standard. This is why it takes an enormous about of time , processor speed and storage.