Converting an audio file into a text document costs a lot of computing resource. When you want an acurrate result , It costs more. It means that your computer’s cpu/gpu have to operate at full load for quite a long time. So, mostly we don’t do it in our own personal computer but on cloud. Here is a audio to text service provider: bluebee.cc. open the website and upload your file. you will get a text file in a while. The service is not free but charges a small amount of money.