By "discretion" to you mean officers revealing private/personal info or images (such as going to the bathroom)? In that case, you allow the officer to turn the system off for preset intervals (say, 5-10 minutes), with the understanding that if an arrest or alteration were to coincidentally happen during that shutdown period, the officer's account would be treated with extreme skepticism - and multiple occurrences of incidents happening during shutdown periods would be grounds for termination.
If by "discretion" you're talking about officers using their judgment in the field to let offenders go without citation, I don't see why video changes anything. Law enforement would still have the discretion to charge or not charge, and if anything, the video would be helpful to supporting that officer's discretion and for training purposes as examples of the right/wrong way to do things.
Turning of a chest-mounted camera while going to the bathroom? If you have to loop your penis up in front of your chest and back down to use the urinal, just wrap it back around waist instead, to avoid having it appear an camera. The most private thing they're going to catch is the sound of you passing gas while using the restroom.
