Heads I win, tails you lose is not credible. It's just riot bait.
That would be a 5th Amendment violation, and possibly a privacy matter.
Police body cams are somewhat widespread. But many on the left here, including BLM apparently, are against them. For example: https://fox17.com/news/local/black-lives-matter-nashville-re...
As a practical matter, though, being able to pick and choose only the most inflammatory and out-of-context audio/video pretty much ruins this as a real source of truth.