Time base correction (TBC) is a technique to reduce or eliminate errors caused by mechanical instability present in analog recordings on mechanical media. Without time base correction, a signal from a videotape recorder (VTR) or videocassette recorder (VCR), cannot be mixed with other, more time-stable devices such as character generators and video cameras found in television studios and post-production facilities.

Time base correction counteracts errors by buffering the video signal as it comes off the videotape at an unsteady rate, and releasing it after a delay at a steady rate. A sync generator provides the timing reference for all devices in the system. By adjusting the delay using a waveform monitor, the corrected signal can be made to match the timing of the other devices in the system. 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.

Though external TBCs are often used, most broadcast-quality VCRs have simple time base correctors built in. Some high-end domestic analog video recorders and camcorders also include a TBC circuit, which typically can be switched off if required.

As far back as 1956, professional reel-to-reel audio tape recorders were mechanically stable enough that pitch distortion could be below an audible level without time base correction. However, the higher sensitivity of video recordings meant that even the best mechanical solutions still resulted in detectable distortion of the video signals and difficulty in synchronizing with other devices. A video signal consists of not only picture information, but also sync and subcarrier signals. Sync allows the image to be framed up square on the monitor and allows the combination and switching of two or more video signals. The subcarrier is involved in reproducing colors accurately.

Implicit in the idea of time base correction is that there must be some target time base that the corrector is aiming for. There are two time bases commonly used.

Some TBCs featured drop-out compensation (DOC) that enabled videotape flaws caused by oxide defects to be temporarily concealed. The DOC logic required dedicated cabling between the videotape player and the TBC in which irregularities were detected in portions of the video image. Previously captured and stored lines of video would then be superimposed over the flawed video lines.

A variant of the time base corrector is the frame synchronizer which allows devices that cannot be steered by a sync signal also to be time base corrected or timed into a system. Satellites, microwave transmitters and other broadcast signals as well as consumer VTRs cannot be sent a sync signal. The synchronizer accomplishes this by writing the incoming digital video into a frame buffer memory using the timing of the sync information contained in that video signal. A frame synchronizer stores at least a full frame of video. Simultaneously the digital video is being read back out of the buffer by an independent timing system that is genlocked to the house timing reference. If the buffer over or underfills, the Frame Sync will hold the last good frame of video until another full frame's worth of video is received. Usually, this is undetectable to viewers.

A modern fifth and final type of TBC developed in the late 2010s is software-defined. The python based project LD-Decode (and its extended versions VHS-Decode and CVBS-Decode) implement this software time base correction method. The programs take in raw PCM (or FLAC compressed) radio-frequency captures of analogue media signals, directly for baseband signals such as composite video but also applies de-modulation for tape formats before correcting the signal in software, this workflow is called FM RF archival in the common use context of tape media preservation.^{[citation needed]}