If it's for media storage, I wouldn't bother making a fusion drive. Fusion drive is just the marketing term for the software layer Apple uses to combine the two physical drives into a pooled storage. Basically, the SSD fills up until it's full and then the rest "spills over" on to the HDD. Based on access of certain files, that's what ends up on the SSD.
If you're using it for media storage though, and are considering a fusion drive, the implication is that you have more media than would fit on the SSD. In this case, the vast majority of it won't be on the SSD and therefore won't benefit from the speed boost. While there might be a subset of media files you access more frequently, in general, you're probably going to pull files all over the place, so I would just put it all on the HD and forget this whole fusion drive business altogether.