Based on the following article:
- http://johnliu.net/blog/2017/10/serverless-connect-the-dots-mp3-to-wav-via-azurefunctions-for-powerapps-and-flow
- https://kamdaryash.wordpress.com/2020/02/05/create-a-pdf-file-of-text-converted-from-speech-recorded-in-powerapps-using-azure-cognitive-services-part-2/
FFMPEG download