The A/V Sync Analyzer Feature allows synchronization measurements between multichannel audio and video within

a signal path. It enables simultaneous timing measurement of up to 4 A/V Sync input test signals in Testor Quad mode

or 1 A/V Sync input test signal in 4K mode.

To use this measurement methodology, an A/V Sync Test Signal is required, which is passed through the signal path to

 be measured. This Test Signal contains video markers and audio markers. The video marker is a black cross (usually referred to as the Black Flash) which flashes every few seconds (in the most standards it is repeated precisely every 4 seconds).
The audio markers are gaps in the tone that starts off with an exact timing relationship to the Black Flash. Testor A/V Sync Analyzer supports the “GLITS” (BBC) audio test signal standard.

It is also possible to compare the video with discreet audio instead of embedded audio.