Trouble running automator shell script

Question

This is probably going to be an really simple fix, but I'm have trouble building an automator service that runs a bash shell script. All of the elements of the script work fine when plugged into shell, but for some reason the automator service is failing to run. The script calls ffmpeg to convert an audio file:
for f in "$@"
do
  fn="${f%%.*}"
  /Users/aa/Applications/ffmpeg/ffmpeg -i "$f" -acodec libmp3lame -q:a 7 -ar 8000 -ac 1 "$fn.mp3"
done
The script runs fine without the ffmpeg command, and the ffmpeg command runs fine in the terminal on its own. Where's the error coming from?
Thanks!

Answer 1

The first is what I'm getting from the bash terminal execution, the second from automator. I'm accenting the differences I see. Thanks for the help!
----bash----------------------------------------
drwxr-xr-x@ 67 aa  staff  - 2278 Apr  6 07:42 .
  com.apple.progress.fractionCompleted  14
0: group:everyone deny delete
uid=501(aa) gid=20(staff) groups=20(staff),12(everyone),61(localaccounts),79(_appserverusr),80(admin),81( _appserveradm),98(_lpadmin),33(_appstore),100(_lpoperator),204(_developer),398(c om.apple.access_screensharing),399(com.apple.access_ssh)
0
-bash
TERM_PROGRAM=Apple_Terminal
SHELL=/bin/bash
TERM=xterm-256color
TMPDIR=/var/folders/x9/y4r_w7gj4_j_3wkfxn6s6fqm0000gn/T/
Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.oSzc5cau0v/Render
TERM_PROGRAM_VERSION=343.6
TERM_SESSION_ID=AF09D92C-2CB4-4069-A172-0DE12EB226BD
USER=aa
SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.RFhFIs94Ad/Listeners
__CF_USER_TEXT_ENCODING=0x1F5:0x0:0x0
PATH=/Applications/anaconda/bin:/Applications/anaconda/bin:/Applications/anacond a/bin:/Users/aa/anaconda/bin:/Applications/anaconda/bin:/Applications/anaconda/b in:/Applications/anaconda/bin:/Applications/anaconda/bin:/Library/Frameworks/Pyt hon.framework/Versions/3.4/bin:/Applications/anaconda/bin:/Users/aa/anaconda/bin :/Applications/Anaconda/anaconda/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbi n:/opt/X11/bin:/usr/local/git/bin:/usr/local/MacGPG2/bin:/usr/texbin
PWD=/Users/aa
LANG=en_US.UTF-8
XPC_FLAGS=0x0
XPC_SERVICE_NAME=0
SHLVL=1
HOME=/Users/aa
LOGNAME=aa
DISPLAY=/private/tmp/com.apple.launchd.YewceoE69R/org.macosforge.xquartz:0
_=/usr/bin/printenv
----automator----------------------------------------
/Users/aa
drwxr-xr-x@ 66 aa  staff  - 2244 Apr  6 07:42 .
  com.apple.progress.fractionCompleted  14
0: group:everyone deny delete
uid=501(aa) gid=20(staff) groups=20(staff),12(everyone),61(localaccounts),79(_appserverusr),80(admin),81( _appserveradm),98(_lpadmin),33(_appstore),100(_lpoperator),204(_developer),398(c om.apple.access_screensharing),399(com.apple.access_ssh)
0
SHELL=/bin/bash
TMPDIR=/var/folders/x9/y4r_w7gj4_j_3wkfxn6s6fqm0000gn/T/
Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.oSzc5cau0v/Render
USER=aa
SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.RFhFIs94Ad/Listeners
__CF_USER_TEXT_ENCODING=0x1F5:0x0:0x0
PATH=/usr/bin:/bin:/usr/sbin:/sbin
PWD=/Users/aa
XPC_FLAGS=0x0
XPC_SERVICE_NAME=0
SHLVL=1
HOME=/Users/aa
LOGNAME=aa
DISPLAY=/private/tmp/com.apple.launchd.YewceoE69R/org.macosforge.xquartz:0
_=/usr/bin/printenv