Increasing compressibility

[JohnGalt]

Hello all. I'd like to start a discussion about the ways that we help to increase compressibility (and hence to minimize artifacting) of sources that we are backing up. I think that this would be a helpful topic for those new to RB -- and helpful to me, of course, as well! If you're new to this subject, the idea is that by removing detail from a source, one makes the source easier to compress, as in general more bitrate is needed to encode (the movement) of fine details. If you get rid of some detail, then more bits can be devoted to the grosser (and more important) detail in the picture.

I tend to use the option "Half-D1 and Half Space for extras" in order to maximize the space devoted to the feature. Of course, the extras then have a tendency to look rather macroblocky since I'm permitting them so little bitrate. In the past I used KISS on the extras by adding to the filter editor in RB's Advanced tab:

e:Undot().Deen()

Undot removes noise, and Deen is spatio-temporal smoother, which "blurs" the image to a certain extent. This Undot/Deen method, sometimes referred to as KISS, works quite well, but it does smooth the image quite a bit -- even too much, I find.

For the past several months, I've been using the Rainer Wittmann's RemoveGrain (http://www.removegrain.de.tf/) filter in mode 17 on extras. I've been quite happy with this system: it decreases macroblocking (almost) as well as KISS, but it also manages to retain a more detailed, less smoothed picture, at least to my eye. Also, RemoveGrain works much more quickly than does Undot/Deen. To use the filter, you must download it (see link above) and put it in your AviSynth filters directory. Then add to RB's filter editor:

e:RemoveGrain(17)

Very occasionally for difficult main movie sources, I'll use RemoveGrain(2) on them -- this mode has a lighter touch than does mode 17.

Does anyone have other suggestions about good ways to increase source compressibility, especially when dramatically limiting the bitrate available to sources?

[blutach]

If you want to maximise space allocated to the feature, blank all the extras.

Regards

[steptoe]

It was suggested elsewhere in another thread to use the segment editor to reduce the bitrate for some parts of a DVD or movie, so increasing the bitrates to the most important parts

Is this what you mean instead of using filters on the entire source



This way you can reduce the bitrates on some extras that say show nothing but still images and also reduce the birate on the start/end credits to boost the rest

[JohnGalt]

It was suggested elsewhere in another thread to use the segment editor to reduce the bitrate for some parts of a DVD or movie, so increasing the bitrates to the most important parts. Is this what you mean instead of using filters on the entire source

What you describe is effectively what I do as well (but without the fine-tuning) when I set RB to reduce the space allocated to extras (through Half/Half or through the 10%/25%/50% options). I simply wondered whether anyone would like to share his or her methods for increasing the compressibility of video -- of extras in particular, especially when one further reduces the bits allocated to them through any of these means that we've outlined.

[Sharc]

Using Redistribution one can achieve the same perceptual quality at a somewhat lower average bitrate (smaller filesize) because of optimized bitrate allocation between segments.
Using RB-Opt one may even run a separate redistribution pass for the Extras and for the Feature respectively, optimizing each in itself.

Another potential optimization of the bits usage is to crop the black borders and then add them back such as to ensure that the active picture fits the mod16 rule. This prevents that the encoder has to encode sharp transitions between the active picture and the black borders which is very bit consuming.

These measures do not actually increase compressability, they rather ensure that the bits are used most efficiently.