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A_Pleite
1st February 2002, 17:30
I'm just programming a smart bitrate calculator, but i'm not sure how to calculate the frame-overhead

I've tried to figure it out of gknot, that are my results:

-3 KB will be used every time
-about 2,4 KB per 100 frames will be used without audio
-about 6,3 KB per 100 frames will be used with vbr mp3
-about 10,2 KB per 100 frames will be used with 2xvbr mp3

Is that right?
Can you give me better formulas?
what about acm-audio?

thanks for helping

A_Pleite

mean
2nd February 2002, 18:00
The formula is :

For each frame (audio or video) 8 bytes in body
+ 16 bytes of index
+ about 8k of avi header.

If you got 1:1 interleaving

Size=8k+nbframe*2*(8+16)

A_Pleite
3rd February 2002, 20:10
Thanks a lot!!

If you have 2acm-audios, is it still the same (size = 8K + nframes * 3 * (8 + 16) ?

What about vbr-mp3?

A_Pleite

A_Pleite
3rd February 2002, 20:49
Gknot seems to want more bits for overhead (just a few):confused:

The thing about vbr mp3:
I think it uses 40 Byte instead of 24 for one frame,right?

A_Pleite

mean
4th February 2002, 08:05
In the body for each frame you got
FCC (4bytes) Size of frame (4 bytes)
For the index
FCC(4) Position(4) Flags(4) size(4)

You may have a round-up error as the total chunk must be even
So if the size is odd , there will be one extra byte to align the structure.

If you are using nandub, it creates a new chunk for each mpeg3 frames, and there may be more mpeg3 frame than video frames.

To be sure, open your stream with vdub and see if the # of audio frame is much bigger that audio frame.

A_Pleite
7th February 2002, 19:48
Ok, i just let the program calculate 40Byte for each (vid)frame in vbr-mp3-stream and 24 in a normal one. In a 3h video the differences between the gknot-overhead-calculation and mine is just 128KByte with a 2-vbr-mp3 Video. I think thats not too much.
I'could make the program going public. Should I (its a bitrate calculator which calculates Overhead, EndTitles, Resolution and Bitperpixel -disadvantage: visualbasic-dlls (math) have to be installed) ?