Applescript: ruta a los archivos en los recursos de la aplicación

   set myPath to POSIX path of (path to resource "audio.m4a")

    do shell script "afplay " & quoted form of myPath

o

 set myPath to POSIX path of (path to resource  "audio.m4a" in directory "Stuff")

do shell script "afplay " & quoted form of myPath

Debería mirar las bibliotecas en la ventana de la biblioteca de Script Editor.

En este caso StandardAdditions

Intentar:

 set pathA to POSIX path of (path to desktop as text) & "test.app/Contents/Resources/Stuff/audio.m4a"
-- or 
set pathB to POSIX path of (path to home folder as text) & "Desktop/test.app/Contents/Resources/Stuff/audio.m4a"

do shell script "afplay " & quoted form of pathA