Time base correction is a technique to reduce or eliminate errors caused by mechanical instability present in analog recordings on mechanical media, including video tape recorders and videocassette recorders. Time base correction counteracts these errors by inserting a variable delay in the video stream, then adjusting this delay in real time so that the output signal appears at precisely the right rate and time.

Most broadcast-grade VCRs have simple time base correctors built in. In addition, cameras and other video devices, such as character generators or digital effects devices have highly accurate clocks that can be precisely adjusted, using a waveform monitor and a vectorscope, to match the timing of the other devices in the system. A single master clock or "sync generator" provides the reference for all of the device's clocks to lock to. If all of the devices in a system are adjusted so their signals meet the video switcher at the same time and at the same rate, the signals can be mixed together.