I think I understand the meaning of the word "jive".
But I still think that something (such as "I'm" or "you're" or something) is omitted before "jivin" because it's being used as a verb in this case, "Jivin, man." because verbs need subjects. For example, people can say "Coming." when then are called by someone and they want to say "I'm coming." So, "(I'm) coming."
So I'd like to know who (or what) is being jiving here, when someone says "Jivin, man."
Also, is there any chance that "jivin" here means smoking malijuana?
I see in dictionaries that the noun form of "jive" means "malijuana" as a slang, but I'm not sure about when it is used as the verb.