Both the Blu-ray and HD DVD formats will feature a new audio watermarking DRM technology, following the announcement that Verance has made its VCMS audio watermark technology immediately available for licensing.  The AACS Licensing Authority originally approved the Verance watermarking technology for use with AACS protected content back in 2006.  In the coming months, AACS is expected to release final agreements which cover requiring the inclusion of VCMS/AV detection technology in HD DVD and Blu-ray players.  As a result, movie producers now have the option of including audio watermarking in their HD DVD and Blu-ray titles.

This audio watermarking technology works by modifying the audio waverform to include inaudible digital codes, which can be picked up by recording devices and decoded by the HD player.  This DRM technology will help AACS by identifying if a watermarked recording was sourced from a pre-recorded source to even illegal camcorder footage taken from a cinema showing.  The technology can monitor and track distribution and control usage throughout the life of the recording.  As the audio itself is watermarked, it will be preserved even if the content is broadcasted or distributed online.

Warner Bros, Sony Pictures, Universal Studios and Microsoft have licensed the technology and Sony is hoping that this technology will help combat illegal cinema recordings.  However, even with this technology, 20th Century Fox believes that AACS protection is not enough and will be making use of BD+ technology in upcoming Blu-ray releases. 

From what I can see, even if this watermarking technology forces upcoming Blu-ray and HD DVD players to rejected recordings which have suspect watermarks, it will have minimal effect on those who watch their recordings on their PC or who have converted their backup copy into another format to watch on a HD network media player where this VCMS/AV detection technology is not present. 

Finally, as HD DVD and Blu-ray have the capability of holding high fidelity lossless audio, adding watermarks that can be picked up by camcorder's internal microphone shows that significant audio modification needs to take place to make the watermarks this robust and in a way defeats the purpose of having these supposedly lossless audio formats if the audio ends up being modified anyway!  Also, watermarks that may be inaudible to the developers of the watermark could be audible to someone else.  

Further information can be read in this source PC Pro article.