This question was posted in response to the following article: http://help.adobe.com/en_US/premierepro/cs/using/WS29F692D2-7A49-44db-A109-AE016B766767.ht ml
The "MTS" file extension is not supported for speech to text conversion. This is apparent as the "Analyse" button is greyed out. By changing the MTS file extension to M2V, speech to text will work. Adobe is aware of this fault but has not noted it in the Knowledge Base. Adobe Support advised me that a lot of people are experiencing the fault. There is no apparent downside to changing the file extension within Premiere Pro.