I’ve got mp3 file with length ~21m55s.
After I import it into the Audacity It became ~21m44s.
So, I’ve made a flack from original track and imported it. From flack I got ~21m53s.
Better, but why it differs?
You could see in attach “Tracks.jpg”. There are two identical tracks, but one was mp3 and other one is flac.
At the beginning they are not shifted!
I’m using Audacity 2.1.2.
In what app are you reading the MP3 file’s length? If it’s a variable bit rate MP3, not all apps can read the file length accurately. Some apps may read an accurate length from the file’s TLEN metadata tag, if that is included.