[patul]

Am a lazy person and never care enough to find better solution, but for multiple files operations, I usually just create a batch file, by first creating the list of the files to be processed:

dir /b *.mkv > output.txt

Then I will open the output.txt in text editor, using column mode, add the additional commands. In your case will be

C:\Portable\MediaInfo\MediaInfo.exe --Inform=file://C:\Portable\MediaInfo\loninapleton.txt " ==> as prefix
" >Your_info.txt ==> as suffix

If it's too complex to handle using text editor, I would use excel instead. Then I will save it as batch file (*.bat) and run it.

There's also PowerShell that can do this in one liner set of commands using pipes, but I've never been particularly fond of PowerShell.