How should I format audio files for custom greetings?
Since Twilio encode the audio for Talk (calls and greetings) in G711 M-ULAW then the custom greetings uploaded to Zendesk should be uploaded in the same format.
The spoken word is by its nature, MONO so you should create a greeting file that is MONO (phone calls are also mono... stereo is needlessly big), so a WAV file encoded in G711 M-ULAW similar to the below. This encoding can be done in many Digital Audio Workspaces and one popular one to use is Audacity.
Please ensure you have no other meta data like album artwork as this is not necessary and just takes up space.
If you upload audio in a different format to whats recommended above you may experience something like this: Agent uploads a greeting via the Talk UI. It sounds crisp over the UI, but when someone calls in and hears it, it sounds grainy, solution? encode it in G711 mUlaw.