Is compressibility check a reliable indicator of a movie demands in bitrate ?

[iparout]

Hi.

I am curious about how accurate a compressibility check is. Is it 100% certain that a scene with a higher Bits/(Pixels*Frame) value is more demanding in bandwith than a scene with a lower value ? The reason why I ask is because when I encode TV-series episodes and need to fit more than one episodes on a CD, the bitrate at which each episode is encoded is relevant to the Bits/(Pixels*Frame) value it outputs after a compress. check i.e. if I need to fit two episodes on a CD and the first one demands a 0.258 B/(P*F) value and the second one a 0.200, I give higher bitrate to the first episode and lower to the second, so that their compressibility check % is almost the same. This gives me, for example, a 400 MB file for the first ep. and a 300 MB file for the second one. Theoritically, although the eps are encoded at different bitrate, their quality must be the same since their compressibility check % is te same. Is this correct ? And again, is a compressibility check a reliable indicator of a movie's demands in bitrate, so as to calculate each episode bitrate like I do ?

Thanks in advance.

P.S. : In the past I used to encode each episode according to the output fileside, i.e. if I had to fit 2 eps on an 800 MB CD, I calculated the bitrate so as for each episode's DivX files to be 400 MB, regardless of the compressibility check. Is this a better way than the one I am currently doing ?

[manono]

Hi-

What you mentioned in the first paragraph is definitely the way to get equal quality for the 2 episodes on the CD. Run the compress test, and then change the file sizes around until the percentages are more or less equal.

Your previous method of giving each episode half of the CD, while a bit easier to set up, can lead to great differences in the relative quality of the 2 episodes.

[iparout]

Yes, that's what I figured also...

[wingphil]

in this case I always link the two sets of vobs into one d2v project, encode as one movie, and then split them afterwards - then you'll always get equal quality - it'll be more accurate too coz it'll be based on the first pass info rather than the compressibility check.

[manono]

Hi-

in this case I always link the two sets of vobs into one d2v project

Yes, that's another solution, and it will insure absolutely equal quality between the 2 episodes. But I can see 2 problems, one minor. When you do it that way, the keyframe will be set at the first black frame, and maybe the music isn't finished yet, or the second episode starts with a lot of black. But the sometimes serious problem, and this happens a lot with anime episodes, is when the first episode ends with a fadeout, and the second begins with a fadein. Then there will be no keyframe set at all. You can always reencode between the keyframes and insure that the keyframe is set at the right place, and then splice it back in, but it's kind of a pain.

Of course, you can check before encoding to make sure that there's no fadeout, and that a keyframe will be set, and if so, then your solution is even better. Good suggestion, wingphil.

[iparout]

Very useful info, manono... Joinhin 2 d2v projects is a real pain and full of problem, unfortunately.

[wingphil]

you don't need to join two d2vs, just make one big one out of the original vobs in dvd2avi.

generally i only do this with tv episodes which have at least some credits either end, otherwise you might miss a annoying second or two, yes.