2,6,A or E is what the second digit of your MAC address must be otherwise a lot of OS's will not work. They will say the NIC is down/not connected even though it is.
This is because if the second digit is not set properly it will not view as a valid MAC or device uplink. This is especially an issue with VMs whether in QEMU etc.. if you are making your own MAC.
MAC address is invalid
c4:d1:aa:e5:10:05
To fix it just........
M4A is a weird format, so you have to be creative here is a quick copy of what I did.
Basically you need to convert to .wav to make use of them and thenI converted the resulting .wav into an mp3 (nice small file size and basically universally playable):
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sudo apt-get install mpg321 mp3gain faad normalize lame
faad "Voice 002 (copy).m4a"
faad "Voice 002 (copy).m4a"........