There is no key to go directly to the next or previous video or audio.
I personally used SPlayer out of my own choice to try it and found its interface very smart. I normally use Pot Player and its kind of one of the best except the fact that, it can not handle some videos properly and even it stumble down when changing audio tracks time to time. However as I am also experienced with MPC HC and VLC, so I think I can give you guys some suggestion to make SPlayer the best as I can definitely see enough potentials in it. So upgrade this great player and make it the best by adding the things I have suggested. I dont know Chineese or Japaneese. So if my suggestions are already given and you are working on it, then I am sorry to disturb you. Whatever, as a fan of SPlayer I am waiting eagerly to see a new version of SPlayer with all the desired characteristics. Thanks.