If you are trying to convert speech from an audio (for example .m4a file) to a written text, you will have to use a special transcription service.
One of such great services is for example VoiceBase, where users can upload their audio files and get transcript texts. You can register account for free an get 200 audio and 20 video hours of computer transcription for free, with an option to order human transcript. But you can most likely find several other such services available on the internet.
Updated: September 26, 2016