The most obvious mp4 to txt conversion likely represents the process of creating a transcript from a multimedia file (for example .mp4) and saving it as a plain text file, essentially audio (speech) to text conversion.
To achieve this you will need some special transcription platform, for example VoiceBase. The resulting text file may require some manual editing however, because computer transcription is not always flawless.Open MP4 file Open TXT file
A voice recognition and converter software
A Voice Search & Transcription Platform