The analog hole is a perceived fundamental and inevitable vulnerability in copy protection schemes for noninteractive works in digital formats which can be exploited to duplicate copy-protected works that are ultimately reproduced using analog means. Once digital information is converted to a human-perceptible form, it is a relatively simple matter to digitally recapture that analog reproduction in an unrestricted form, thereby fundamentally circumventing any and all restrictions placed on copyrighted digitally distributed work. Media publishers who use digital rights management, to restrict how a work can be used, perceive the necessity to make it visible or audible as a "hole" in the control that DRM otherwise affords them.
Overview
Although the technology for creating digital recordings from analog sources has existed for some time, it was not necessarily viewed as a "hole" until the widespread deployment of DRM in the late 1990s. However, if high-quality equipment is not used to perform the conversion, the resulting copy may have distinguishable low fidelity compared to the digital original. Regardless of any digital or software copy control mechanisms, if sound can be captured by a microphone, it can be either recorded by analog means, or stored digitally. And if images, including text, can be seen by a camera, they can also be recorded. In the case of text the image can be converted back to text using optical character recognition. In the case of streaming music services, software exists that can digitally capture the analog output of a personal computer's sound card, and then save in a portable music format with no perceptible loss in quality.
Response
In 2002 and 2003, the U.S. motion picture industry publicly discussed the possibility of legislation to "close the analog hole"—most likely through regulation of digital recording devices, limiting their ability to record analog video signals that appear to be commercial audiovisual works. These proposals are discussed in the Content Protection Status Report, Consumer Broadband and Digital Television Promotion Act, and Analog Reconversion Discussion Group. Inventors of digital watermark technologies were particularly interested in this possibility because of the prospect that recording devices could be required to screen inputs for the presence of a particular watermark. The motion picture industry has also pursued several private-sector approaches to eliminating the analog hole; these might be implemented without additional legislation.
Analog signals can be degraded in ways that interfere with or confuse some recording devices. For example, Macrovision attempts to defeat recording by VCRs and DVD players by outputting a deliberately distorted signal, crippling the automatic gain control for video, causing the brightness to fluctuate wildly. While this is only supposed to happen to copies, it may, as an inadvertent side-effect, happen when viewing the original video as well. Some vendors claim to have developed equivalent techniques for preventing recording by video capture cards in personal computers. Devices exist, however, to counteract this measure.
Manufacturers of recording devices can be required to screen analog inputs for watermarks and limit recording as a condition of private contracts. For example, a manufacturer who licenses patents or trade secrets associated with a particular DRM scheme might also be obliged as a purely contractual matter to add recording limitations to digital recording products.
Manufacturers of certain playback devices such as set-top boxes can be required, as a condition of private contracts, to allow publishers or broadcasters to disable analog outputs entirely, or to degrade the analog output quality, when particular programming is displayed. This capability is one example of selectable output control. A broadcaster could then prevent all recording of a broadcast program by indicating that compliant receiving devices should refuse to output it through analog outputs at all. On some of the latest playback devices, analog outputs have been eliminated completely.
In theory, it is possible to bypass all these measures by constructing a player that creates a copy of every frame and sound it plays. Although this is not within the capability of most people, many bootleggers simply record the video being displayed with a video camera or use recording and playing devices that are not designed to use the protection measures. In fact, the Motion Picture Association of America has recommended use of a camcorder as an alternative to circumventing the Content Scrambling System on DVDs.
The notion of "plugging the analog hole" may be based on fundamental misconceptions of the meaning of analog and digital. There is a history of business and political desires combined with core misunderstandings of technology leading to legislation and industry practices that are counterproductive or fundamentally flawed on an engineering theory level.
