I wouldn't worry about sounding naive, patents can be complex and most (if not all) of the general population do not have an understanding of patent law. Asking a question on Avvo is a good first step to figure out how to proceed.
I may be a little confused about your question, but I am not sure of your purpose in having a stranger reviewing your recording and am not sure if you are referring to an audio/visual recording or the what you are actually drafting up to describe your idea. If you are looking for a way to prove that you were the inventor, actually having some witness that would not be required; filing an application is enough to make the claim that you are the inventor and you will not need to go about proving that unless someone challenges it and has evidence that you are not. If you are looking for someone to review your draft to make sure you have not made any mistakes in calculations, etc., then you would want to get an NDA. If you are looking at someone to review the recordings to prove date of conception, recent changes to patent law in the U.S. has changed so that it is is first-inventor-to-file and conception date would not make a difference unless when the invention was conceived could effect something like ownership.
If you are looking for someone to review your recordings to make sure you have not made any mistakes, you would want to have an NDA. There are generic NDA's available, but I would highly recommend having an intellectual property/patent attorney draft the NDA that is specific for your situation so that you make sure you are covered (it is often much cheaper to hire an attorney to draft an NDA than to miss out on the opportunity to patent something). The attorney will also be able to give you an idea as to whether your idea would be patentable and if you are at a stage where you can obtain a patent (abstract ideas are not patentable, so you would have to be at a point where the idea is embodied in patentable subject matter).
I would highly recommend meeting with a patent attorney to get an idea of what progress or next step you need to perform to obtain a patent. You can try to clarify a little more on here about what you are referring to when saying "reviewing my recordings" and seeing if you end up with more helpful answers, but MAKE SURE NOT TO DISCLOSE ANYTHING ABOUT YOUR IDEA ON AVVO! It is a public forum and disclosing it on Avvo could cause the idea not to be patentable.
Answering of your question is merely general advice and does not constitute legal advice. None of the statements or implications made by this answer creates an attorney-client relationship with the attorney answering the question. The statements made in this answer are not to be solely relied upon and you should meet with a competent attorney to discuss any concerns you may have regarding this answer.
You don't need to have someone "record" your work leading to an invention at every state. Many companies have systems in place wherein scientists sign each page of their laboratory noteooks as they are written and have a witness in the laboratory initial it. Some companies believe that this is unnecessary. There is no right or wrong answer. You certainly can use friends, relatives or anyone else to witness your execution of the notebook pages (or other records showing development).
The most important thing is that you keep accurate records concerning how, when and where you developed your invention. Further, you should retain patent/intellectual property counsel at an early stage to advise you concerning how to protect your invention and begin the process of preparing your patent application. The safest way to "record" the development of your invention is to provide your records to IP counsel.
As my colleagues indicated, this is a complicated area, and there is a lot of "garbage" out there that almost sounds like "old wives tales." There is no need to record your idea. The best way to protect yourself is to file a patent application. There is no "poor man's patent." In other words, simply writing your invention down and mailing it to yourself is almost worthless. The United States is now a "first to file" country, which means that protection goes to the first person to file a patent application. Therefore, you need to consider contacting a patent attorney for some help with filing at least a provisional patent application. The links below may provide you with some assistance.
The answer to this question is for informational purposes only and does not form an attorney-client relationship.