For audio files encoded with fixed bitrate it's clear that the programs shows this value as encoding bitrate.
However, I'm wondering what the program shows when a variable bitrate is used. Is this the maximum, minimum or average used bitrate of the file? And is this value calculated by the program by analyzing all frames or taken from a VBR tag?
I think that in that case for VBR files the comparison may show in many cases lower "real" bitrates compared to the case if they were fixed bitrate.
For VBR audio files it seems to me that the program never shows a "real" calculated bitrate higher than the encoding average value.. While for fixed bitrate audio files the 'real' calculated bitrate in many cases certainly is not the average bitrate.
For example a file with fixed bitrate 320kbi/s, which will show an encoding and calculated 320 kbi/s. This is Ok since 'sufficient' 320 kbi/s is present in the file (although average will be closer to 256kbi/s (probably even somewhat lower):
A VBR audio file (same music) which shows both as 256kbi/s for encoded (average) and real calculated bitrate in the list is given below:
As can be seen in the examples, based on the frequency spectrum the VBR 256 kbi/s file actually has still many
frequencies higher than 256 kbi/s present (as expected) and are also more if compared to the fixed 320 bitrate.
For this case it's not very important since I can't hear anymore +18000 Hz .... But sometimes VBR files has lower average bitrates and in that case seem to be lower quality compared to the fixed bitrate files.
So it should be logical that the programs calculates the real bitrate in the same way as for the fixed. As a consequence the encoding average can be lower than the "real" bitrate for such files (in this case real 320 kbi/s / encoding 256 kbi/s).