I guess I should have been more clear: real-time but not live or automatically published. If it's automatically published then many people may be reticent to begin recording. For example, maybe you don't want the fact that your friend or family member is being arrested to immediately become public knowledge or otherwise shared, embarrassing video and all.[1][2] If in the end there's no police misconduct, the whole incident can remain relatively private. Yet if it turns out you're recording misconduct then it would be important that the footage be uploaded in real-time in case the cop (or anybody else) destroys your phone.

FWIW, I abstain from Facebook, Twitter, and social media in general. Apologies if Facebook Live or any other suggestion does support this.

[1] I'm white but grew up in home environments where the police were called many times, sometimes hauling someone away kicking and screaming. (Typical unintended consequence of alcohol abuse and otherwise bad life decisions, albeit all too common life decisions in poor America.) You have to be sensitive to such situations, especially in the modern electronic era where it's extremely difficult to escape past mistakes.

[2] The arrest could have been mistaken, in which case you definitely don't want a video of it getting out unless there was actual police misconduct or possibly even if there was police misconduct.