BNC or Coax?

I have heard that BNC beats coax for video

Once again, BNC is a connector, and coax is a cable, so your question is unanswerable. Assuming you mean to ask whether a BNC connector is better to use for both video and digital audio than an RCA connector, the answer is yes (although either connector could very well be acceptable in both cases).

Regards,
-- Al

As Almarg says, coax is a cable. The name is a short form of "co-axial", which means that the central conductor and the woven shield share the same axis in cross-section.

Also as he says, you can fit an RCA connector or a BNC connector to a coaxial cable.

You could also fit twin-lead cable to an RCA connector but IME it would be a bit harder to do that with a BNC.

Other connector types can also be used with coax cable. Phone plugs for example.

BNC is the only true 75 ohm connector. SPDIF is not ( if that's what you meant by coax). Therefore, BNC is always better then RCA (SPDIF) for digital transmission.

Thank you Kyomi. Your reponse was very helpful.

kyomi_audio:
SPDIF (Sony Philips Digital InterFace if I recall) is the protocol transmitted across the cable, and is used whether the coaxial cable is terminated by RCA or BNC connectors.

The SPDIF protocol includes left and right channel audio data, flags (e.g. to indicate pre-emphasis), subcode information (e.g. track and disk/track time info), and clock.