Outout filesize is sometimes higher than expect. why?

[yanosh]

I use DVD Dec and Auto Gordian to rip my dvd to divx.
I've set the Target Quality to 75%.
I rip it chapter by chapter.

Now the weird thing is that I get sometimes low file size and sometimes high filesize for the chapters.
For example:

Chapter2 on the cd is 1:30min and the size I get is 17.3mb.
Chapter3 on the cd is 3:31min and the size I get is 140mb.


Could it be because the video quality on the dvd is not the same on all the chapters?

[manono]

Hi-

No, it's because the video quality is the same in all the chapters. I'm assuming that all the other settings, such as the resolution, are the same for the 2 chapters. Most likely, Chapter 2 is a static scene or series of scenes, and requires a much lower bitrate to achieve that 75% quality, and Chapter 3 is a much more complex (or action packed) scene or series of scenes, requiring a much higher bitrate to achieve the same quality. The bitrate difference between the 2 chapters is on the order of 3.5, and that's not at all unusual.

If you'd like to confirm that, then run the 2 chapters through DRF Analyzer (http://www.geocities.com/analyzerDRF/), and the average quant of the 2 chapters should be very similar.

[Tuning]

Originally posted by yanosh
Chapter2 on the cd is 1:30min and the size I get is 17.3mb.
Chapter3 on the cd is 3:31min and the size I get is 140mb.

Hi manono,

Isn't duration difference affect the final size in quality mode?

Here the second chapter is almost 2.5 times longer than 1...Just a doubt.

[yanosh]

Tuning - the second chapter is almost 2.5 times longer than 1 but over 8 bigger than it.

manono - I understand you. I never knew that the movement effects the size.
140mb for 3 and a half mins is quite a lot and if I set the target quality below 75% I'll lose much of the quality I guess.

Can you give me a suggestion because I'm a inexperienced in this business?

[manono]

Hi Tuning-

I wondered if anyone was going to call me on that one. I did it in an instant in my head, so I'll work out my reasoning for you:
Chap 2=90 seconds
Chap 3=211 seconds
211/90=2.34
2.34x17.3=40.48
140/40.48=3.46 Not bad for a quick head guess.

yanosh, as you know, you lose all control over file size when doing a quality encode. If you think the sizes are too large, then maybe you'll consider lowering the resolution in Advanced Settings. But even if you do a regular 2 pass encode of the 2 chapters, I think the size of chapter 3 when compared to that of chapter 2 will be similar to what you get with Quality encoding. It just requires a higher bitrate to achieve similar quality. If you do a 2 pass encode, you could set a file size limit for Chapter 3, but then its quality will be less than that of chapter 2. You may or may not notice the difference. If it really is a chapter with a lot of action, often your eye can't tell the difference.

But I agree that those are some pretty large filesizes, given the length of the chapters. Maybe the scenes are very difficult to compress, with not only lots of action in Chapter 3, but a lot of noise or film grain to make the compression doubly difficult.

If you really want to do them with good and similar quality, but lower file sizes, I might suggest doing them in the full Gordian Knot. By doing that, you'll have access to the temporal and spatial filters that can make them more compressible. Except for using Undot, AutoGK doesn't (yet) have any way to help the compressibility when in Quality Mode.

For more about the relative complexity of different scenes, please see point 21 of the Log Window portion of the AutoGK Guide. (http://len0xmirror1.serveftp.net/~len0x/tutorial/AutoGK.html#5)

[Tuning]

Originally posted by manono
[B]Chap 2=90 seconds
Chap 3=211 seconds
211/90=2.34
2.34x17.3=40.48
140/40.48=3.46

Thanks for clarifying the doubt.:)