JPEG is a well-known standard for compressing stills. Unlike MPEG, M-JPEG compresses and stores every frame rather than only the differences between one frame and the next. Thus it requires more space than MPEG, but it is more efficient when rapid scene changes are involved, and easier to edit. It is capable of a variety of compression ratios, typically between 2:1 and 12:1. At 5:1 or lower, its deemed broadcast quality. Higher than that, up to about 12:1, is more than acceptable for semi-professional or consumer purposes.

The M-JPEG codec works best when contained in microcode on a video capture card chip. When implemented in hardware in this way the PC’s main processor is left free to concentrate on other tasks, such as maintaining the required hard disk data transfer rates. The algorithm can also be worked into a software codec, which allows video to be seamlessly edited in applications such as Adobe Premiere.

Despite its role as the workhorse of the digital video universe, the future is looking uncertain for M-JPEG. The new DV format has spread like wildfire through the professional and mid-range video market. It’s totally digital, offers better picture quality than analogue-to-digital conversion can ever hope to achieve and has industry heavyweights Sony and Panasonic behind it. More importantly, it’s custom-designed to bring real-time, high-quality video editing to the desktop PC.