Blu Ray Rendering – MPEG2 quality versus AVI

[John Rofrano]

Is the quality of MPEG2 video equivalent to (or even better than) AVI? Is the file size of AVI simply related to being directly ready for Windows?

AVI is just a container. It’s a “wrapper” for any number of codecs. MPEG2 is a wrapper and a codec combined. Depending on the codec that you use in an AVI file, the files can get very large. They can, however, also be smaller than MPEG2. It all depends on the codec used. The quality is determined by the codec inside the AVI file and the bit-rate.

Most AVI codecs use intraframe compression. This means that every frame is a complete image that stands on it’s own. There is a physical limit to how much these can be compressed. MPEG2 and some AVI codecs (like DivX and Xvid) use interframe compression. This is where frames are grouped together in what is called a “Group Of Pictures (GOP)” where only one frame contains the while image and the other frames contain delta and predictive information about only the parts that have changed since the frame before. With this scheme you can get much higher levels compression and thus much smaller files at almost the same quality. So it is not the file type as much as it is the codec inside.

~jr

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[Kevin Caulfield]

Thanks, John. So there is very little noticeable difference in quality between MPEG-2 and AVI?