I was processing some 56k bitrate mono mp3 files, and noticed a discrepancy of around 10 secs in the duration reported by mp3tag compared to the actual playing time from foobar or mp3directcut.
I duly checked the files with both mp3VAL checker and VBR fix but no issues reported.
It's not a major problem really, but I thought I'd mention it as I'm curious to know why.
In regular intervals, you find reports about the variation in bitrate for VBR files.
Apparently, the first few frames are important for MP3tag to calculate the length. If these are longer or shorter than the rest in average, you get an inaccurate result.
This is nothing to worry about. It is just that MP3tag simply does not look at the whole audio part.
If MP3val and Mp3diags have not reported anything, fine.
If you want to get matching results, transform the file into a CBR file (e.g. winmp3packer).
BTW: reports about the length differences have so far been categorized as "no bug".