You can use a pre-recorded audio file in wav, mp3, ogg, oga or r16 format. If the audio file included in a Voice API call is not playing, it is very likely due to an encoding incompatibility.
While all formats of mp3, ogg, oga and r16 should be supported, only the following is supported for wav:
- Unsigned 8 bit PCM
- Signed 16 or 24 bit PCM
- u-law or A-law encoding