There is another thing about codec comparisons.
They are not fair:
DivX is an MPEG codec. That means that it shows a certain
kind of compression artifacts:
Typical MPEG artefacts are blocks and mosquitoes. Here are 2
captures from the music clip George
Michael & Whitney Houston "If I told you
MPEG produces Blocking Artefacts in scenes with many changes (=fast
movements, scene change, a lot of motion). See the capture above
(Britney Spears "I love rock 'n' roll"): This
is a frame where there was a scene change, there's a lot of
funny paper flying around and she's dancing.
Really blocky. Would you believe when I told you, that the sound
to this picture was aired in mono (instead of stereo)? 64kbit/s?
Mpeg Layer 2? On a music channel (MTV India)? Modern TV Quality.
As another artifact MPEG produces Mosquitoes at sharp contrasts like mouth/skin,
ocean/sky, dark hair/bright wall. See around Whitney's mouth and
eyes (no, it's not because she just came from a cocaine
Sometimes you see compressed text in the internet like
these message boxes with their typical artefacts. I created these sample message boxes:
JPEG artefacts around the text.
GIF artefacts: Clear text, but less colors (see the title bar
and the question mark).
If you take footage, that has already been compressed by
another MPEG codec, then you amplify those artefacts.
So if you record a digital TV broadcast and then encode it with DivX
this means, MPEG-2 (broadcast) is encoded with MPEG-4 (DivX).
The same applies to DV (which also uses MPEGlike compression methods) and
DVD (which is MPEG-2). VCD is MPEG-1 and SVCD is MPEG-2.
But not only that compression artefacts are increased, to
compress them it takes more bandwidth (in theory), of course: Because how should
the codec know what is an artifact and what is part of the
image? So it has to encode the artifacts also. Thus you increase
artefacts AND file size. I have made experiments though, that show, that
file size actually decreases when recompressing. Why? Because
DivX blurs and darkens footage when compressing and compresses better when
blurred. So each recompression makes your movie more blurred
(and darker) and
thus compresses better.
That means, to be fair you'd have to compress a RAW clip and
To see how re-encoding (re-compressing) affects the quality
see my recompression