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I figured.
That being the case, the problem now becomes where to get the correct voltage to clamp the signal to? I read somewhere that to do it accurately/reliably enough, you would need a DAC. Idea is that you use a microcontroller to set the DAC to an accurate black level, then use the LM1881 to clamp the signal to the DAC generated voltage. The McGyver in me says there's another way, though.
The article I referenced in my first post mentions a comparator in the feedback loop of the video amp: why not use the LM1881 to trigger the comparator, thereby stabilizing the black level before the beginning of each horizontally scanned line?
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