rockbox/manual/plugins/vbrfix.tex

\subsection{VBRfix}
This function scans a VBR (Variable Bitrate)
MP3 file and updates/creates the Xing VBR header. The Xing header
contains information about the VBR stream used to calculate average bit
rate, time information and to more accurately fwd/rew in the stream.

This function is especially useful when the playback of a file skips,
fwd/rew does not work correctly or the time display is incorrect. Run
VBRfix on files you record with your Jukebox. The header is not present
in the recorded files and VBRfix adds this header.

\note{VBRfix can only run when music is
  turned off (since it uses the same memory as the player) and can take a
  while to complete if run on big files.}