GOP Structure Impact on Quality

[TheFamilyMan]

I am always in seach of the "best" quality for my VHS to DVD conversion projects. Does GOP structure really have a impact on picture quality? I know that there are the 'silly' examples like all I frames, which should produce a totally uncompressed clip, or GOP like I1P2B6 (which I'm not sure is legal). But it seems if the encoder is up to it and the bitrate is sufficient, any reasonable GOP structure should work as well, quality wise, as the next for DVD compliant MPEGs. Any thoughts on this?

P.S. I'm not fishing for the best GOP, though it maybe that certain encoders work best with certain GOPs. I'm just interested in the theorical statement and its pratical implications. Thanks......

[bugster]

If you are really interested in dufferent GOPS, take a look at www.kvcd.net

In general, the longer the GOP (no of frames between I frames), the greater the chance of artefacts and thus lower percieved quality. GOPS shorter than those used by DVD standards, you probably wouldn't see much quality improvement over.

I know that there are the 'silly' examples like all I frames, which should produce a totally uncompressed clip

Not quite true. An I frame IS compressed. It is compressed in such a way that it can be uncompressed without reference to any other frames, just like a jpeg or Gif image is uncompressed without reference to other images. B and P frames both require references to ther frames before they can be generated/uncompressed.