There do exist dedicated transcription services and solutions, for example VoiceBase that can transform the speech from a multimedia file (for example AVI) and save the words in a text format (.txt, .text or whatever). It may not always be perfect and commonly requires manual editing.
Convert Audio Video Interleave movie to Text file.
We found one software available in the database for this conversion.
On-line services software - convert avi to text on web
A Voice Search & Transcription Platform
Convert from avi file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.