This problem is Hard if implemented the way suggested in the question. It becomes easy with pathauto if you use two separate vocabularies: video_topic and photo_topic. Then, video_topic could have pathauto paths that start with video/% and photos can have paths that begin with photo/%.
Consider: if you use a single vocabulary, then clicking on the link video/% would show both videos and photos. Same with photo/%. If this is what you want, then perhaps the path you should use should be topic/% instead of video/% and photo/%. If you do want the results to be shown separately, then separate vocabularies are definitely the way to go.
If you want to keep your video/% and photo/% vocabularies in sync, then you could add a video topic in code every time a photo topic was clicked, and visa-versa. It's important to consider how you want your system to behave, though, as that will drive the solution and implementation that you'll want to choose.