[MEncoder-users] AVI overhead

[Rich Felker]

On Fri, Nov 11, 2005 at 03:05:39AM -0800, Jean Hoderd wrote:
> Hi,
> 
> My encodings with XviD are constantly running above the target
> size, and I suspect it might be the avi overhead.  I am using
> these formulas to compute the video bitrate:
> (rates are in kbps, duration in seconds, sizes in bytes)
> 
> audiosize = 1000 * audiorate * duration / 8
> videosize = totalsize - audiosize
> videorate = 8 * videosize / duration / 1000
> 
> Now, this set of formulas does not into account the avi overhead.
> (The videosize should be totalsize minus audiosize *minus* overhead).
> My question is: how does one compute it?  (At least an estimation)

AVI overhead is 24 bytes per frame plus some small initial overhead
for the file header. So just multiply by the number of frames and you
have overhead. Keep in mind this 24 bytes is for ALL frames, not just
video, and audio is typically around 35-45 fps.

Rich