There are a few hurdles before charges can be laid. Video evidence is regularly used in courts these days and when paired with testimony from an eye witness (police or otherwise) it can be quite compelling. If we can satisfy the basic requirements to lay a charge, referred to as reasonable and probable grounds that an offence has been committed, it's good to go.
I know a lot of officers may not use this approach because it results in a he said/she said in court. I think that the video itself is what tips the scale and that it's worth it to try. Ultimately it doesn't matter what the police think, it is up to the prosecutor to be willing to send it to trial, and a JP that is willing to convict.
Just my perspective.