Which format is better for explaining complex things online: Videos or Infographics?

For explaining many complex phenomenon, a picture can be worth a 1000 words. Videos can be even more engaging than still pictures, but they make it really hard to focus on a specific part without having to use back & forward controls.

When does it make sense to spend all the time & money required for videos instead of graphics?

I'm looking for evidence regarding: 1) Under what circumstances people learn better from videos than from still graphics (like infographics) 2) Under what circumstances people generally prefer to have videos instead of still graphics.