Wouldn't the engines be much louder than that?

Not while taxiing and you're losing a ton of fidelity on that shitbox microphone on that phone with matching shitbox video quality.

Also looking inside the engine looks empty, can't see any rotors like in these photos.

"Looks" empty. But it's not. Again, shitbox phone cameras favor bright light. The shadows are sharp enough here to cause the camera to completely wash out most of the detail in the dark shadows in favor of being able to see the areas lit by the sun.

Here is a version of the video that is slightly (only) better quality that better shows the turbines as the plane passes.

Wouldn't the engines be much louder than that?

Not while taxiing and you're losing a ton of fidelity on that shitbox microphone on that phone with matching shitbox video quality.

Also looking inside the engine looks empty, can't see any rotors like in these photos.

"Looks" empty. But it's not. Again, shitbox phone cameras favor bright light. The shadows are sharp enough here to cause the camera to completely wash out most of the detail in the dark shadows in favor of being able to see the areas lit by the sun.