If the by-law is not registered, then it is probably not enforceable. That is certainly the case in the ACT where I am more familiar with the relevant Act.
I think the EC could and should provide support to the victim’s complaint to the police. It could provide written comment along with the DVD that in their opinion the DVD, even without sound, appears to provides ample evidence of assault, not to mention a breach of the OC’s by-laws.
It is difficult for the EC to act as police. The EC’s letter could also go to the offender informing that person that they have provided the police with video evidence and noting that the video is evidence of a breach of the by-laws (perhaps omit to mention that it does not have sound). That could be considered a warning. It is fair to tell both/all parties that the video is being provided to the police, so the letter should be sent to all parties. The letter and video could be sent regardless of whether the victim chooses to press charges or not.
I think the above would be procedurally fair and may be enough for the victim to feel that the matter is taken serious and he or she is supported by their neighbours. It also would tell the offender in a clear, unambiguous way that the behaviour was unacceptable.
Transparency, copying to all parties, is looked on favourably by courts.