system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: TV commercials cut out after 1 second and play another?

Is it a problem in the control room of the TV station? Is it overbooking of commercial spots? Why do I sometimes see a commercial play for about 1 second, and then it cuts out and another compliantly different commercial plays instead?
gpt
Commercials could be from two or three sources. The network has a commercial there and the local station then cuts that one out and places a local one in its place. There are signals that tell them when a commercial is starting and sometimes the equipment starts the local one a little late. 

In Canada we see this more as a lot of commercials are replaced with Canadian versions vs US versions. 

In Canada we see very few of the US commercials during Superbowl and the US stations are replaced with Canadian ones.