A few weeks ago on a NRT-SFO flight, my seat mate's video/audio system was non-functional. This was a 777.

I asked for the compensation form and we filled it out, and the purser apologized several times and said he would submit the form. We left blank the part about what the problem was.

I was shocked when United sent a $400 travel voucher about 2 weeks later. I doubt that's the official compensation amount for an entertainment system error, but who knows.

The point is, it's probably fairly unpredictable, aside from whatever the official policy is.