This is bullshit.

1. Barring moronic applications of zero tolerance laws (which are mostly limited to schools), the police are almost never required to enforce every law that they witness being broken. If there were such requirements, then the average cop would get in their car, spend 6 hours trying to drive to the end of the block, then turn around and spend the next 6 hours driving their car back. THERE ARE COUNTLESS CASES of police officers being followed by camera crews, witnessing somebody breaking a law, and then letting them off with a warning. Just watch any episode of COPS.
   
2. Police departments in most states have broad authority to withhold information from public records requests when no charges were made, a person was charged but not convicted, or a person accepted deferred adjudication. This includes body camera footage.
   
3. Body camera footage currently enjoys some of the most lax public records request requirements of any form of information collected by law enforcement. Because collecting, sorting, storing, and retrieving video footage is very costly, most agencies limit requests to a specific piece of footage (date, time, the name of at least person who is either wearing or being filmed by the camera).
   
4. Most departments give police broad authority to decide when their cameras will be turned on or off. This allows them to enter private residences, talk to sensitive victims and witnesses, etc. The situations in which they are required to turn on their cameras are pretty common sense: felony investigations, use of force, situations where somebody has requested backup.

The reality is that there would be no reason for a cop to record himself making marijuana disappear. If he did record it, there would be no reason for him to save that footage. If he did save it, there would be no reason for the department to retain that footage. If they did, there would be no reason for them to turn it over. If they did, absolutely nothing bad would happen to anyone involved, as is evidenced by hundreds of hours of televised reality cop shows depicting cops letting people off with warnings.