media\/([^\/?]*+) might work if you're only interested in that specific pattern. I was trying to test it but it seems to keep crashing my page.
For reference here's a good doc on regex in Dynatrace: https://www.dynatrace.com/support/help/organize-monitored-entities/reference/how-do-i-use-regular-expressions-in-dynatrace/
the split actually puts multiple values on the request, so that is not what you want here.
instead of that remove the split ad do a regex that will go for the second part. this regex should do the trick, it jumps over part one and takes part two.