DVD to DivX - Compression and file sizes

[clarenceb5]

I am not entirely new to DivX but I don't understand all the ins and outs of compressing DVD to DivX but I do know that I do really like using AutoGK. I am only curious about one thing, why is it that some DVDs converted to DivX using AutoGK are much smaller in file size that other movies that have approximately the same running time? Thanks in advance.

[killingspree]

This is a matter of compressability.

In short depending on quite a lot of factors like amount of movement, brightness and special settings like water just require the codec to allocate more bits to certain frames. Now depending on the total amount of those 'high-bitrate-scenes' the movie can either fit on one cd with good quality, or, even if it has approximately the same length only fits on two cds with acceptable quality!

AutoGK does a so called compressability test which estimates how good a movie is going to compress and uses the results to decide if it should go for one or two cds.

You can take a good look at this phenomen by examining the codec shoot out (http://www.doom9.org/codecs-203-1.htm) doom9 conducted at the end of 2003 (also earlier installments of the same tests showed the same results). while the movie 'The Matrix' compresses surprisingly well and easily fits on one CD, some people will not be satisfied with the quality of 'Saving Private Ryan' even if they compress it for a two CD rip.

if you have any more questions feel free to ask!

kr
steVe

[clarenceb5]

Thank you for your explanation, I was aware that there are some scenes in movies that require a higher bitrate, but I had no idea how complex it is, thanks again for your answer and extremely quick responce.

[clarenceb5]

I just remembered something that I forgot to ask. Is it at all possible that the file size of the outputed DivX avi file created with AutoGK can be much greater than the file size of the vob file outputed with DVD Decrypter? I had this happen if no one else has seen it, I tried to convert a Pearl Jam DVD to DivX using AutoGK and I can't remember the exact file sizes but the vob file outputed from DVD Decrypter was approximately 5 gigs and the outputed avi file from AutoGK was approximately 9 gigs using 100% quality. Is this due to the fact that the video was mostly in the dark and the bitrate needed too be high to keep a clear video which causes the file size to be so large?

[killingspree]

no actually something definitely went wrong there... but we would need a lot more information to determine the cause of it.

steVe

edit: PS: Tom where did your post go?!

[manono]

Hi-

killingspree-I deleted it, because as soon as I posted it, I saw that you had beaten me with a more detailed answer.

In my opinion, nothing went wrong with clarenceb5's encode. It's not unusual, under certain circumstances, for MPEG4 compression to produce files much larger than the original DVD. And it seems like those circumstances occured with his rip of the Pearl Jam DVD. I haven't ripped that DVD myself, but in general, concert DVDs are notoriously difficult to compress.

With concert DVDs, you frequently have full screen 1.33:1 interlaced video (29.97fps if R1), you have low quality grainy footage, you have flashing lights and all the other stuff common to concerts, and most of all, you have handheld cameras constantly shaking, panning, and zooming. If handheld, the screen is in constant motion, and this works against compressibility.

If the final size bothers you, my suggestion is to redo it for 2 passes, maybe 3 CDs (2100 MB), and set a minimum horizontal resolution of 512. Even if you come out with a low compression percentage, if I'm correct about the source being grainy, it'll still look fine. If you don't want it split, then set it up for a Custom Size for 2101 MB, or something like that.

Or, if you still want to do a 1-pass quality encode, lower the quality to 50% and set the horizontal resolution to 512.

[killingspree]

Originally posted by manono

In my opinion, nothing went wrong with clarenceb5's encode. It's not unusual, under certain circumstances, for MPEG4 compression to produce files much larger than the original DVD.

And you are of course so right :) - oh my god - i think i should learn reading before posting any more 'help' :scared: