First, you have to understand that a composite (RCA) video connection contains both Luma (brightness) and Chroma (color) information together. The first step in capturing video or displaying it or processing it is to separate these two signals from one another.
One must use a filter in order to achieve this. There are a few kinds of filters that do this. The most successful ones are comb filters. One side effect of these comb filters, however, is an effect that occurs near borders of objects. The artifact, called dot crawl, occurs when high frequency luma passes into the area where the filter thinks it's not a luma signal anymore. You can also see this artifact when someone wears a "noisy" tie on TV, which turns into a mess on the display.
An adaptive comb filter is supposed to be smart enough not to be fooled by this. It is supposed to be intelligent enough to separate the two without having information cross over from one to the other.
, that described the evolution of y/c separation circuits through the ages... if I run across it again, I'll post the link.
