Do unofficial testimonies and civil recordings hold value in the US courtroom?

Question

As far as I know admitting to something while not under oath has no value, as it should. But if there is a case against you with some other solid evidence can an unofficial/not under oath confession be used against you in the US courtroom? And for that matter is confessing to a police officer while not under the oath of the courtroom considered a valid confession?

Also, does recorded audio or video by a civilian, for example, hold value in the US courtroom?

The reason I am asking is because in my country:
1. Any confession or testimony NOT made to a police officer or other similar legal party (we don't have oaths) is completely meaningless. This is because when speaking to a police officer, as he is considered an official representation of the law, etc. you are required to recognise the gravity of the situation and speak only truthfully, therefore anything you say is taken to be truth and can be used as valid testimony.
Similarly if you just randomly tell someone you killed someone you could be joking, not of sound mind, etc. and that is why such a confession is worthless.

.2. Audio or video footage not recorded by a police device or other officially recognised device, such as a security or traffic camera, is also worthless as you can never say for certain said footage is unedited or not inscenuated, i.e. that someone did not hire actors to look like you and perform a crime.

EDIT:
After some more researching it turns out I was wrong. Confessions to a police officer hold a lot more value than ones, say, made on the internet, but the ones on the internet could still be used in court, albeit almost noone would take them seriously for the aforementioned reasons.

Confessions to civilians, however, are different because in that manner the civilian appears in the form of a witness, which has value.

As for audio and video recordings it turns out it doesn't matter if they are made by a civilian or a security camera, both can be used in court but rarely have too much value for the aforementioned reasons.

In the end here, and as I believe elsewhere, you need more than circumstantial evidence to successfully convict a person (you need witnesses, direct evidence, etc.).

Answer 1

Your confessions, to anyone, can be used against you. If A admits to B that A stole the car, B can testify to what A said. In fact, if B accuses A of a crime and A says nothing (and C witnesses this), C can testify as to what B and A said (or didn't say) – this is known as an adoptive admission, and it is up to the jury to decide if they think the silence is significant. Recordings are likewise admissible. All evidence is in principle defeasible, so if there is a video of "you" committing a crime, you can make the case that it wasn't really you, and the jury will weigh the evidence to see if they are firmly convinced that you did commit the crime (at least in New Jersey... long story about 'burden of proof').