There is an issue with Scratch Live 2.4.3 that is causing this. This will hopefully be resolved soon. In the meantime, you can either revert to Scratch Live 2.4.2, or in Scratch Live 2.4.3 enable and then disable Serato Video in the Plug-ins' tab of the Setup screen (this will allow the faders to work). It's unfortunately that Apple removed the input functionality from the audio port. I imagine that it wasn't being used by the majority of their customers. So, for this model, you would need either an external audio-interface, or to record the audio portion of your mix within Scratch Live (and then add it to the recorded video later).
