The problem is that you have a "special" hyphen followed by a space before the "g" in the middle of your command line, it is known as an "en dash" and it is confusing your parser.
To compare:
Hyphen: - Em dash: — En dash: –
Your script should be (to the best of my knowledge):
cd c:\ffmpeg\bin set inputFile="C:\park.mp4" set outputFile="C:\content\park" ffmpeg -y -i %inputFile% -c:a libfdk_aac -ac 2 -ab 128k -c:v libx264 -r 24 -g 24 -b:v 1500k -maxrate 1500k -bufsize 1000k -vf "scale=-1:720" %outputFile%_720.mp4
I would assume that the article you copied the script from was created using some kind of word processor which automatically substituted the em-dash after a space was accidentally typed before the "g" and from there it got copied and pasted into the rest of the article.
Hint garnered from this SO question