6. What are the copy protection schemes used in DVD ?
What is Macrovision ?

There are many forms of content protection that DVD technology employs. The two most popular and well known methods of video copy protection are Macrovision and CSS. Most if not all DVD players are equipped with the required electronic circuitry to prevent direct video tape copying from a movie DVD disc with a process known as Macrovision. This process, also known as APS (Analog Protection System), or copyguard, yields the copy as a series of random stripes of color, picture scrolling with distortion, random black and white picture sequence, dark and light cycles of images with saturated color information.

Macrovision technology appeared in the mid-1980s on videocassette tapes. By the end of the 1980s, most major Hollywood studios were utilizing the Macrovision technology. The technology was then extended to DVD players.

Macrovision destroys the backup copy by changing the composite video and S-Video analog signal to make it not viewable. It creates a rapidly modulated colorburst signal and inserts pulses in the vertical blanking signal. This method damages the electrical synchronization and automatic-recording-level signal in more than 90% of consumer VCRs and therefore renders the tape copy useless.

The DVD specifications allow DVD program material to contain bit fields to instruct the DVD player whether or not to enable copy protection with Macrovision. Not all DVDs are copy-protected with Macrovision. Macrovision or any APS method affects only the video portion, not the audio part. However, Macrovision protection can be bypassed easily either at the software or hardware level. Most DVD rippers and DVD backup software can fill in the appropriate bit fields in the program material to remove the Macrovision copy-protection request from the original program material. At the hardware level, inexpensive devices known as video stabilizers can effectively defeat the purpose of Macrovision and even enhance the video image stability.

Some DVD players provide option to disable Macrovision during playback. Some DVD players can be configured to ignore Macrovision bit fields from the video stream altogether. In the United States, the fair use law, as interpreted in "Sony Corp. vs. Universal City Studios", which ruled that the making of individual copies of complete television shows for purposes of time-shifting does not constitute copyright infringement, but is considered fair use. However this legal aspect has changed somewhat with the Digital Millennium Copyright Act. By late 2001, the sale, purchase, or manufacture of any device that has no commercial purpose other than disabling Macrovision copy prevention was made illegal under this act.