Ok looks like it did work. When vtt files are parsed then the Content will not show on the Media Attachment page like it does for the txt files. Looks like the content of the VTT file can be searched and those posts where vtt files are attached will find the keywords but the search results terms will not show up. No excerpts seem to be found for the vtt files.
Do you think that vtt file content is unable to show up in the results? if so then I can just txt files.