Resisting arrest is not the same as resisting abuse. Merely mouthing off to a cop isn't grounds for the officer to escalate the confrontation to physical force, especially when the arrested person is already in handcuffs.
The police officers probably wrote their reports before they realized they were on video. I would love to see copies of how they described the event to compare it to the video of how it actually happened.
Finally, this is yet another example of how cameras can keep cops professional. EVERYONE behaves better when they know they are being videoed. These cops didn't know a camera was watching, so they acted however they wanted to act.
You probably have a cell phone and it probably has the ability to record video. Use it.
Better yet, download my iPhone App and use that, since it also records your GPS location and emails the video to me before it can be deleted.