View Full Version : making the size perfect in Divx4

11th February 2002, 14:24
Hi, wise guys!

I'm using Gknot to make my rips. But I'm experiencing problems concerning the size of my finished movie. Usually my rip is 0-30MB undersized (rendered and muxed). Because reencoding means a few hours extra I had the following idea:

1) Doing the calculation for video AND audio in GKnot (using for example "120kbit ABR" as value for audio to calculate the video bitrate; 120kbit cause the end bitrate will be typically higher caused by the undersized movie file)

2) Rendering ONLY the video in Gknot

3) Comparing the Video-AVI file size with the desired file size and calculating the audio bitrate that will fill up my avi to the desired file size after muxing

I think this is a good compromise for me between extra work and using the full size, because Audio Encoding is done in a short period of time compared to video rendering.

My Problem is step 3. I don't know how calculate the VBR overhead (when audio encoding is done in G-Knot it is doing this for me.)

Can you help me? Have you any experience doing so this way?

11th February 2002, 18:38

Instead of encoding the video first, try encoding the audio first. This way you won't have to worry about an overhead or anything.

Gordianknot gives you the option when setting your bitrate to use an existing audio file on your hard drive.

This way, the exact size of the audio file will be known and the video bitrate will be configured to match.

also, remember that the video bitrate calculator, esp. for Divx 4.12, is not as exact as 3.11.

This is because Divx 4.12 calculates 1MB=1000 kilobytes. Windows uses the old way of 1024kb=1MB, as does Divx 3.11.

So your calculations in DivX 4.12 are going to be off from the beginning. Gknot realizes this and errors on the side of caution. Would you rather have a movie 20mb under your desired filesize or 20mb over. I know which I'd rather have.

I know I don't explain it very well.....let me know if you don't understand what I am saying.


11th February 2002, 20:41
That is exactly what I did until now.

The reason is not that GKnot is calculating the wrong values. It's Divx4 that does not deliver the desired filesize for me.

So if there is someone who thinks I want to blame GKnot here; that's not the thing.

There IS a problem with undersized files in Divx4. At the beginning I thought, that I am too stupid to do it, but as I read on I found many users experiencing the same problems.

So the thing I've described in the last post is MY workaround cause I don't want to reencode over and over again.

Could someone help me and give me the formula to calculate the frameoverhead that VBR MP3 introduces.

Thank you very much.

17th February 2002, 09:07
Try using DivX4Log.
Guide in http://www.everwicked.com