My question involves a traffic ticket from the state of: New Jersey

Today I was driving on Rt. 1 in central NJ in the middle lane. In the right lane was another car, followed by a police cruiser. I needed to get to the right lane to make a turn. I took note of the police cruiser and made sure I pulled a safe distance ahead, and changed lanes carefully. The cruiser then pulled me over and issued me a ticket for 39:4-126 (failure to signal) and 39:4-88b (unsafe lane change). I am very certain that I used my turn signal (and that it is functional) and that I changed lanes safely. This took place in a safe corridor so I'm looking at 4 points + $400ish in fines. My driving record is otherwise clean.

I know I have the option to plead to unsafe operation for a $450ish fine and 0 points if the prosecutor is willing to cut a deal. However I am also very upset at the officer, and would like my day in court to prove my innocence out of principle. The police officer told me that he had a dash cam in his car. If I go to trial, the only way to avoid a losing she-said he-said situation is if I can discover the video and if it clearly shows that I am right.

My questions are as follows:

1) Does anyone know how long dash cam footage is preserved?
2) If I get the footage in discovery and it does not clearly establish my innocence, can I still plea bargain with the prosecutor before trial?

Thank you