I'd say it really depends on how bad it is and whether people in positions of power are involved. Best option should be to get involved and show responsibility as a citizen that you will not accept racism in your country. Support the affected person and open your mouth.
I think uploading stuff to social media is a slippery slope. You may be exposing a hardcore racist, but you may also just be destroying someone's life who had a bad day and acted inappropriately. So even if you do decide to film, I would carefully consider whether to upload that video. If there's good reason to get the person fired, well, even then there is the question of whether it needs to be public knowledge or whether there are other ways of making the employer aware.