Historically, video was stored as an analog signal on magnetic tape. Around the time when the compact disc entered the market as a digital-format replacement for analog audio, it became feasible to also store and convey video in digital form. Because of the large amount of storage and bandwidth needed to record and convey raw video, a method was needed to reduce the amount of data used to represent the raw video. Since then, engineers and mathematicians have developed a number of solutions for achieving this goal that involve compressing the digital video data.