Like I said, the Japanese YouTube - youtube.co.jp in other words. In fact, I just did a bit of experimentation, and it seems that the location doesn't matter. At least, I could use the automatic closed captioning whether I had my country set to Canada or Japan. I'm not going to bother experimenting any more than that. Anyway, you just press the little CC button on the lower right of the video frame, if there is one. After poking around a bit, it seems like maybe only videos uploaded by "official" sources (TV networks and the like) offer this option. Or perhaps you have to allow automatic captioning when you upload the video. Or maybe they only allow auto captions for videos that meet a certain bit rate. I'm sure there was a press announcement about the feature somewhere. Anyway, below are three videos that allow automatic captioning. You have to fiddle with the button though - even after clicking CC, you have to hover your mouse over it until the option menu pops up, then select "automatic captions" or whatever (which usually just pauses the video. If this happens, select "automatic captions" from the menu again until a message pops up) than agree to the message warning you that the captions won't be perfect, blah blah blah. After that, you can turn on the translator from that same options menu.
A short Japanese news report.
The ANN Japanese news YouTube channel
A clip from One Piece