Converting recorded wav calls to mp3

First off I would like to state that I know freepbx does not support the mp3 conversion of recorded calls.

With that being said I am hoping someone can help me with my dilemma. I have a bash script running as a cronjob that converts recorded wav files to mp3 files and updates the cdr database. The problem I am having is: If there is an in-progress call when the cronjob executes the portion of the call that has yet to be recorded is "lost". The cdr record is also not changed to the new file. I am hoping that someone knows how to modify the existing bash I am using to only run against calls that are no long in progress or to only run it as a post call script on the call.

Below is the code:

#!/bin/bash
# A Script to Convert FreePBX call recordings from WAV to MP3
# Also updates the CDR database, for correct downloads through the web UI
# Version 1 - 2015/11/15
#
# Copyright Jaytag Computer Limited 2015 - www.jaytag.co.uk
#
# You may use or modify this script as you wish as long as this copyright
# message remains. Redistribution prohibited.
# Set the Asterisk Recording Directory
recorddir="/var/spool/asterisk/monitor"
# Start the Loop, store the path of each WAV call recording as variable $wavfile
for wavfile in `find $recorddir -name \*.wav`; do
# Make Variables from the WAV file names, stripping the file path with sed
wavfilenopath="$(echo $wavfile | sed 's/.*\///')"
mp3file="$(echo $wavfile | sed s/".wav"/".mp3"/)"
mp3filenopath="$(echo $mp3file | sed 's/.*\///')"
# Convert the WAV files to MP3, exit with an error message if the conversion fails
nice lame -b 16 -m m -q 9-resample "$wavfile" "$mp3file" && rm 
-frv $wavfile || { echo "$wavfile encoding failed" ; exit 1; }
# Update the CDR Database
mysql -u root -s -N -D asteriskcdrdb<<<"UPDATE cdr SET 
recordingfile='$mp3filenopath' WHERE recordingfile = '$wavfilenopath'"
# On-Screen display of variables for debugging/logging
# echo ""
# echo "File -------------------------------------------------------"
# echo "Wav File : " $wavfile
# echo "Wav No Path : " $wavfilenopath
# echo "MP3 File : " $mp3file
# echo "MP3 No Path : " $mp3filenopath
# echo "End File ---------------------------------------------------"
# echo ""
# End the Loop
done