I just finished opening 219 gold chests in a row. I don’t recommend doing this, because it took about 4 hours. I had noticed lately that gold video chests seemed very rare, so I stopped opening gold chests for a week. In that week, Wokamon counted 99,790 steps. Here is a list of what I got:
As you can see, I got exactly ONE video chest containing crystals, comprising slightly less than 0.5% of the chests I opened. In fact, it was the very first gold chest I opened. Is that as intended? That seems like a pretty low rate. And this is with accessories adding 8.3% to my video chest chance. My 1900% bonus for gold chest videos isn’t doing me a lot of good like this.
@JustinZ sorry for the late reply, the studio has been crazy busy 
The accessory effect is definitely in place however the chance of showing a video is also dependent on the ad provider. If the ad provider does not have an ad for you, then you will not receive ads.