Digital Audio Tape (DAT)
From Wikimedia Commons
In recorded tapes, this move to digital sound came with the invention of Digital Audio Tape (DAT). The record industry, fearing widespread copying resulting in lost sales, lobbied against it, which meant that it was not widely available for several years. An attempt was made at a copy-protection system based on an analog indication of copy-protected sound using a notch filter, which DAT recorders would detect and prevent copying if it existed, which was called CopyCode that was created by CBS. Unfortunately it had many problems and was widely opposed, as was a bill to mandate it. Ultimately a compromise was reached in 1989 using Serial Copy Management System for copy protection that was based on bits set in the subcode data in a digital link instead, which was codified as a requirement in the Audio Home Recording Act in 1992, along with royalities on DAT devices and blank media.
Audio CD copy protection
Back in the old days, an Audio CD was not easily copyable or rippable. That changed with the introduction of CD-ROM drives which allow easy ripping of music into a computer. Eventually the industry responded with various tricks being used to prevent copying, most of which is not compliant with the Red Book standard and disqualifying these discs from the CD logo, as a result causing issues with some optical drives such as these CDs not ejecting. Another alternative is to put copy protection software on the audio CD. Sony BMG's attempts to do exactly this in 2005 turned out to be a disaster. What Sony BMG did was that they put XCP and MediaMax copy protection software onto some of their audio CDs. Both of these software used a rootkit to hide the software, a technique commonly used by malware, which was exposed by Mark Russinovich. I will not go into the mess that was the attempts by Sony to provide removal tools, which at first had security holes. This fiasco resulted in widespread consumer outrage that increased awareness of the harms of DRM, eventually leading to most music nowadays being DRM-free.
Digital music DRM
When online digital music stores were invented by Microsoft and Apple, the record companies wanted the music to be copy-protected because they feared widespread piracy. As a result, Microsoft and Apple invented DRMed AAC and WMA formats used by for example iTunes Music Store. Many of these formats relied on a centralized license server. In 2008, MSN and Yahoo Music were about to shut down their license servers, which would have meant that operations with the music requiring that server would no longer work. Later MS relented and promises to keep the MSN Music licence servers on until the end of 2011. That was after consumers caught on to the harms of DRM, partly due to the Sony BMG disaster described above, leading to DRM-free music eventually becoming the primary form of online music nowadays.
VCR AGC copy protection (Macrovision)
Macrovision was a form of copy protection for VCR tapes. It used the Automatic Gain Control (AGC) feature of many VCRs to distort the image when copying a Macrovision-protected tape by adding false sync signals. There were several ways to bypass it including using Time-Base Correctors or just turning off AGC.
DVD and Blu-Ray copy protection (CSS/AACS)
When the DVD standard was created in 1996, it came with the Content Scrambling System (CSS). The ways it was supposed to work was that the DVD Copy Control Association would license the keys to manufacturers that needed them under the conditions that the rest of the system be implemented. Unfortunately, it turned out to have many flaws. For one thing, it used weak 40-bit encryption due to US export restrictions that was effective when CSS was created. There were other flaws too. DeCSS was released on the LiViD mailing list in October 1999 that allowed decrypting DVD discs. It was authored by Jon Lech Johansen and two other anonymous authors.
Later on, Advanced Access Content System (AACS) was created for HD DVD and Blu-Ray. It was stronger than CSS, being based on AES instead with a revocation system being used to revoke compromised player, among other things. The primary ways it has been cracked was to compromise the Media Key Block (MKB) used for the decryption in AACS, though other keys such as the title key has been compromised too. When the first one was compromised and published, it was published widely and attempts was made to take it down with the DMCA, to no avail. Fortunately, AACS supported MKB renewals which was done soon afterwards with a new MKBv2 being used from then on. But of course eventually that was compromised too, then another MKB was created, and so on in a cat and mouse game.