If I have multiple AD8194 in series (output feeding one of the inputs to the next device) do I degrade the video quality as it goes from one device to the next? If so, what is the max number of devices that I can place in series?
I do not recommend cascading multiple asynchronous buffers to make a larger multiplexer. Cascading multiple devices will not directly degrade the video quality. Bit errors in the digital video stream usually result in "no picture". Cascaded asynchrous devices can result in increased jitter in the serial data signal thereby reducing the overall signal margin. In most cases the picture will be good, but the reduced margin can present problems during the stressed signal testing in the HDMI compliance test. More information regarding this is described in AN-1166.
Please consider a larger HDMI mux such as ADV3002 (4:1) or HDMI transceiver such as ADV7622 or ADV7630. HDMI transceivers are synchronous (i.e. the serial data is re-clocked), therefore HDMI transceivers can be easily cascaded without any signal quality impairments. Also, for very large fan-in/fan-out scenarios please consider a digital crosspoint switch such as ADN4604 or ADN4605