Compression rate comparisons. Any tool?

[chicola]

I'm totally aware that one should compress a video (DVD or not) to the limit of one's own visual perception. In other words, if it still looks good for me then that's my kind of limit.

BUT...

...most people in these forums talk about the indexes of compression shown by CloneDVD or DVD Shrink as a "certain" measure of quality.

They say, "don't go lower than 70%", "80%", "90%" or "100%".

BUT all these compression ratios are dependent on the duration of the movie and the bitrate with which the DVD was encoded in the DVD, by the manufacturer.

There are originals encoded in 4000/5000 kbps average and others with much higher average rates. Those "talked about" compression limits should be different when deciding on doing further recompressions/transcodings.

So, having all this in mind, does anyone know of a tool which can give an "absolute" compress index based on bitrate and motion analysis? Any published studies in this area?

I hope I made myself clear..

Happy Xmas to all videohelp community.

[Shadowmistress]

I do alot of compressing. I'm not sure I understand your question. If you have a disk that's 4000 kbps and one thats 8000 kbps and you compress them both to 50%, the quality will be the same but the filesize will be different. Are you asking why the filesizes must be different?

[jimmalenko]

If you have a disk that's 4000 kbps and one thats 8000 kbps and you compress them both to 50%, the quality will be the same but the filesize will be different.

I'd disagree there. Some movies "compress" much better than others - something to do with the motion vector operations that the transcoders manipulate I believe.

[Nilfennasion]

It also must be said that the quality of the original source material is a big factor. Those cheapie DVDs of old Marx Brothers or Three Stooges shorts will not respond well to compression unless they have been substantially cleaned up before being encoded. Recent films like the Star Wars prequels, on the other hand...

[skebenin]

The only practical and quick qualitative test I've ever heard of is DDogg's OPV test - Taking the dumbness out of CCE multipass - Revised 6

I'm not sure how, or if, this could be adapted to something like a compression ratio in DVDShrink, but it seems like it should provide some guidance. It'd be an interesting exercise.