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File size of an CBR(Constant bitrate) audio recording can be calculated using a formula:

File Size (Bytes) = (sampling rate) × (bit depth) × (number of channels) × (seconds) / 8

E.g., a 70 minutes long CD quality recording will take up 740880000 Bytes, or 740MB:

44100 × 16 × 2 × 4200 / 8 = 740880000 Bytes 

But it doesn't work if the audio is VBR(Variable bitrate). How to know whether a audio file is CBR or VBR?

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I'm running on Ubuntu 12.04 –  kev May 8 '12 at 10:55

3 Answers 3

up vote 5 down vote accepted

Install Checkmate first (the .deb file) by double clicking it and selecting Install in Ubuntu Software Center.

Then, open up a terminal with CtrlAltT and call:

mpck input.mp3 | grep "bitrate"

This will tell you precisely whether a file is CBR or VBR. If it's CBR, you'll just see the bitrate, and if it's VBR, after the average bitrate label you'll see (VBR).

I tested this on Ubuntu 12.04, but packages for Checkmate are available for Windows as well.

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When I play the audio on player that display the bit rate, for VBR you will see the bitrate always fluctuate. For CBR, the bit rate remain constant throughout the whole songs. I use Winamp to play thought.

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Not entirely true. That may hold for Winamp, but the OP is using Ubuntu. Even VLC doesn't properly show whether an audio file is CBR or VBR. –  slhck May 8 '12 at 10:59
    
@ slhck You are right about VLC, they don't display it correctly. Under Windows, I also check with dBpoweramp and it does display it correctly including the encoder name as well. I don't use linux so I don't know will do the job. –  chmod May 8 '12 at 11:40
    
See my answer on how to reliably check it in Linux. Given that it's command line, it could even be batch-scripted for multiple files or an entire MP3 collection. (By the way, you shouldn't put a space between @ and username, otherwise people won't get a notification). –  slhck May 8 '12 at 11:42
    
@slhck thanks for the tip. –  chmod May 8 '12 at 11:46

This is my trick, it works only if you have a directory containing multiple mp3 files, and you know that they have the same encoding (VBR or CBR): If the files show different bitrates then you know they are VBR encoded.

You see the bitrate indication in the file properties, or use exiftool *.mp3 | grep Bitrate.

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