Convert m4a to wav with 16000 sampling rate
Most speech to audio conversion tools requires a 16kHz sampling rate. Here is how to convert an m4a file to wav with a 16kHz sampling rate using ffmpeg.
ffmpeg -i input.m4a -ar 16000 output.wav
Pass -y to overwrite the output file if it already exists.
Pass -ac 1 to convert to mono audio.