Not quite bar code... but I did something similar quite a while
back in 6800 assembly.  I had a tape drive (from Exatron, I think).  I
used a bar code sort of technique to store data on it.  A short time
between transitions was a mark, a long time was a space.  I then just put
down standard 8 bit asynchronous data.  This was a replacement for the
then standard Bell 202 tones on audio cassette.  On playback, there was
some leading mark codes, then the data.  The software determined had a
period of time it would use to determine whether the incoming pulse was a
mark or a space.  Once the pulse was in the appropriate "bin" and the
appropriate one or zero output, the pulse duration was used to help
determine the tape speed and adjust the transition time between mark and
space.
        Someone else has suggested capturing the barcode to RAM, then
figuring it out, instead of trying to do it on the fly.  It was pointed
out that this could take a bit of RAM.  One way to minimize the amount of
RAM would be to just store the amount of time since the last barcode
edge.  These times could then be analyzed after the scan.

Harold