My post abbreviated the advice of an experienced NLE programmer:
Quote
Don't rely on the FCP scope to confirm the presence of sub-blacks. Their behaviour is flakey, to say the least. Sometimes the scope shows the image being clamped at black, but then you nudge the timeline a frame forward and the sub-blacks are revealed.
Waveform Monitor just did it to me! But it wouldn't do it again, ephemera being what they are. So I emptied caches, restored prefs, and rebooted. This time Waveform Monitor did an interesting dance. The clip is a wedge, so Waveform Monitor shows a ramp. For about a second it showed a ramp clipped at black = 0. Then it changed to the full (bent) ramp.
I suspect FCP's rendering and not-rendering, its strange RT methodology, lies behind Waveform Monitor's misbehavior.
Dennis Couzin
Berlin, Germany