A method of processing supplementary content in a digital receiving apparatus, includes connecting to an external device being different from a broadcaster; receiving uncompressed audio/video (A/V) content from the external device being different from the broadcaster; extracting audio watermark from the uncompressed A/V content, wherein the audio watermark includes domain type information, time information and event flag, further the event flag is used to signal when an event is available, and the event flag is 1-bit; constructing a first uniform resource locator (URL) based on the audio watermark; transmitting a request to a remote server based on the first URL; receiving a second URL for the supplementary content from the remote server; and presenting the supplementary content based on the second URL.