I understand that both hinein and herein can be used to translate "into it", that hinein is used when referring to movement away from the speaker's location, and that herein is used when referring to movement toward the speaker's location. Is all of that correct? If all of that is correct, then what is commonly used when the speaker is a third-party that observes something moving into something else and does not want to reference her own location? Can hinein be used in this case?
For example, a person jumps into a river. She wants to say in mid-air, "I jump into it." One possibility is: "Ich springe hinein." Then a dog jumps into a river and the person (who is already in the river) wants to say "It jumps into it." One possibility is: "Er springt herein."
Suppose now that a person is flying high in a helicopter and looks down. She sees a dog jumping into a river and wants to say, "It jumps into it". Can she say "Er springt hinein"? What is the common way to say this?