08 So how much does it compress? (MPEG-video)
Description
This article is from the MPEG FAQ, by Frank Gadegast phade@cs.tu-berlin.de with numerous contributions by others.
08 So how much does it compress? (MPEG-video)
As I mentioned before, audio CD data rates are about 1.5 Mbits/s.
You can compress the same stereo program down to 256 Kbits/s with
no loss in discernable quality. (So they say. For the most part
it's true, but every once in a while a weird thing might happen
that you'll notice. However the effect is very small, and it takes
a listener trained to notice these particular types of effects.)
That's about 6:1 compression. So, a CD MPEG I stream would have
about 1.25 MBits/s left for video. The number I usually see though
is 1.15 MBits/s (maybe you need the rest for the system data
stream). You can then calculate the video compression ratio from
the numbers here to be about 26:1. If you step back and think
about that, it's little short of a miracle. Of course, it's lossy
compression, but it can be pretty hard sometimes to see the loss,
if you're comparing the SIF original to the SIF decompressed. There
is, however, a very noticeable loss if you're coming from CCIR-601
and have to decimate to SIF, but that's another matter. I'm not
counting that in the 26:1.
The standard also provides for other bit rates ranging from 32Kbits/s
for a single channel, up to 448 Kbits/s for stereo.
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