When a Video Signal is put through a Digital Video Effects mixer (or DVE), you will find that the audio is out of sync due to the processing delay of the Mixer/DVE.
Audio Delay Interface
That's where audio delays come in. An audio delay interface is required because it will allow you to delay the audio until it matches the processor's output. Audio delays are programmable to enable you to precisely match the video signal with the audio signal. They are available in rack mounting and free standing versions.