TotalBitRate = max(audio.nAvgBytesPerSec * 8, FileByteRate).

FileByteRate = FileSize / video.dwLength * (video.dwRate / video.dwScale) / 1000.AudioBitRate = audio.nAvgBytesPerSec * 8 / 1000.I'll spare you all of the experiments I did and just give you the actual algorithm used by Windows Vista Explorer: For some AVI files, it does display reasonable bitrates, but for files written by VirtualDub, it still displays strange values. So, basically, ignore whatever Windows XP Explorer says. I did a test of concatenating an AVI file to itself back-to-back, and the reported video rate doubled. The other thing that's really bogus here is that the video rate is being computed according to the size of the entire file, which includes headers, audio, and whatever junk may be at the end. In this case, the actual video rate is closer to 400 kbps (1 kbps = 1000 bits/second). That's incorrect and confusing, but that's what Windows XP Explorer does.

If you look closely, you'll notice there's a big units problem here - I've computed audio bit rate using SI units (1k = 1000), but video byte rate using binary units (1k = 1024), and labeled both as kbps.

The video data rate is computed as floor(file size / video.dwLength * video.dwRate / video.dwScale / 1024).

The audio bit rate is computed as floor(nAvgBytesPerSec * 8 / 1000).

Windows XP, as it turns out, computes data rates as follows:

audio.nAvgBytesPerSec = 192000 bytes/secįirst, let's start with Windows XP.

Recently, a poster on my forum asked why Windows Vista reports the wrong bit rate when displaying Properties for AVI files written by VirtualDub, compared to Gspot, a common media file analysis utility.Īfter some experimentation, the answer is that it's a combination of some silliness in Windows Explorer and an omission in VirtualDub.įirst, let's take a sample file with the following info (note that I'm particular about which items for an important reason): ¶Why does my AVI file show strange bit rates in Windows Vista?

How to play an avi file for windows xp