The search for faster and more capacious optical storage media is fuelled by the need to distribute video of better quality. This was evident in the emergence of DVD and now in the development of BD and HD-DVD. High Definition (HD) video refers to a video stream that meets or exceeds the resolution of 1280 x 720 pixels. In contrast, DVD Video supports resolutions up to 720 X 576 pixels, and Video CD supports a maximum of 352 x 288 pixels. Non-HD video is also referred to as Standard Definition (SD) video.
MPEG1 is the compression format used in VCDs, while MPEG2 is used in DVDs. The next generation media support multiple compression formats like H.264 (an MPEG4 format) and VC1 (based on Windows Media Video 9), besides MPEG 2. Protection of the video content is also another factor influencing the adoption of newer optical media. Next-generation discs use Advanced Access Content System (AACS) and High Definition Content Protection (HDCP) to prevent unauthorised use.