Matrices? When, where how!

[rendez2k]

I’ve been trying to backup Depeche Modes 101 DVD with limited success (a very awkward DVD with flashing lights, smoke, lots of grain, almost VHS quality video in places and its almost a full DVD9!). Both CCE and HC produce a farley 'blocked' output. So, I decided to try Matrix Editor to try and improve things. But to be honest, I can’t see much of a difference in any of the tests I’ve done. So…. What are matrices, what do they do and when should I be using them? Is there anything I can do do make this backup better?! :thanks:

[jptheripper]

does it have lpcm audio? that can be takin g up tons of space.

[manono]

Good question, jptheripper. If it's the same as the Germen R2 (should be, right?), it has DD 5.1, DD 2.0, and LPCM:

http://www.cinefacts.de/dvd/review/ansicht.php?reid=1593

So, if it were I, I'd immediately dump the DD 2.0, and the LPCM tracks and thus gain back a huge amount of space to improve the video.

About matrices:

Weighting makes use of the fact that human vision sensitivity is not linear with frequency. This means that a fair amount of noise (or lack of data) is less noticeable at the high frequency ranges. Furthermore, noise is less noticeable when masked in highly detailed areas, than when it is present in plain areas.

Now that we have expressed the information in the frequency domain using the DCT, we can manipulate the frequency spectrum of the signal to achieve compression using perceptual coding techniques. Since the human vision is relatively insensitive to high frequency information, we can reduce the amount of information with little impact on perceivable quality...

The quantization matrix is filled with values that depend on it's location within the matrix - small numbers for lower frequency components, and larger numbers for higher frequency components. This quantization matrix is also encoded into the bitstream so that the decoder can always decode the picture.
http://www.iis.ee.ic.ac.uk/~frank/surp99/report/kht97/work.html

As for whether or not you want to change from the default matrices used, that's up to you. First, though, I'd take jptheripper's suggestion and dump the extraneous audio tracks and anything else you don't absolutely have to have and try again.

[rendez2k]

Thanks guys. It was really stupid of me not to notice the LPCM track (considering how many backups I've done!) - It saved loads of space. I'm just re-running it now and I'm expecting good things! Does anyone run HC encoder in best quality rather than normal?

Still unsure about matrices though. I think the description is a little beyond me! Do they normally make a difference? Do some people use them all the time, and if so in what situations?

[manono]

Well, depending on the matrix used, high frequency data will be removed (i. e., the video smoothed) to a greater or lesser degree. And because the human eye is less likely to notice the removal of high frequency detail than low frequency data, a good matrix will allow good compression without you noticing what happened, or in other words, that it's not as good as the original.

Ordinarily, for movies, I use a higher bitrate matrix (i. e., a better matrix) than CCE's Standard matrix, and for low bitrate extras, I ordinarily use a lower bitrate matrix. That's just me though, and different people have different strategies.

Since concert DVDs are notoriously hard to compress for a number of reasons (the flashing lights, grain, and smoke, which you noticed, and the use of handheld interlaced video cameras, frequent edits, low production values, etc.), even after having removed the audio, it may still not be the quality you want. I don't know. But I would guess that compressing your concert DVD might be similar to FredThompson's recent posts about compressing his wrestling DVDs, so you might search out those posts to see what he says, and maybe try out the matrix with which he's had success. And often those kinds of DVDs aren't very good to begin with. So before you go crying "I have blocks!", make sure they aren't in the source as well.

Do they normally make a difference?

In my opinion, yes, a wise choice of matrix can make a big difference in the quality of your backup. Just my opinions. Take them with a grain of salt.

[feedback]

As crusty says concerning a Quantization Matrix "I will try to give an explanation here that is possible to understand even if you're not a math expert".

Moreover, expounding on what manono has already shown you, read the link below.

It is a good long read but I am sure you will glean some info. on Matrices from it.

So, read Understanding a Quantization Matrix Here. (http://forum.doom9.org/showthread.php?t=54147&highlight=work+matrix)

Regards,:)