Motion JPEG (M-JPEG or MJPEG) is a video compression format in which each video frame or interlaced field of a digital video sequence is compressed separately as a JPEG image.
Originally developed for multimedia PC applications, Motion JPEG enjoys broad client support: most major web browsers and players provide native support, and plug-ins are available for the rest. Software and devices using the M-JPEG standard include web browsers, media players, game consoles, digital cameras, IP cameras, webcams, streaming servers, video cameras, and non-linear video editors.
History
Motion JPEG was originally developed for multimedia PC applications.
Early implementations of MJPEG were generally implemented in Hardware. C-Cube was an early proponent with their CL550 JPEG codec been used in several hardware implementations. It was announced that the NeXTdimension from NeXT would ship with an onboard CL550 to implement MJPEG. This was however later shelved and wasn't included in the final product that was shipped.
Apple provided a Software implementation of MJPEG in their QuickTime Player in the mid-1990s.
Design
M-JPEG is an intraframe-only compression scheme (compared with the more computationally intensive technique of interframe prediction). Whereas modern interframe video formats, such as MPEG1, MPEG2 and H.264/MPEG-4 AVC, achieve real-world compression ratios of 1:50 or better, M-JPEG's lack of interframe prediction limits its efficiency to 1:20 or lower, depending on the tolerance to spatial artifacting in the compressed output. Because frames are compressed independently of one another, M-JPEG imposes lower processing and memory requirements on hardware devices.
As a purely intraframe compression scheme, the image quality of M-JPEG is directly a function of each video frame's static (spatial) complexity. Frames with large smooth transitions or monotone surfaces compress well and are more likely to hold their original details with few visible compression artifacts. Frames exhibiting complex textures, fine curves and lines (such as writing on a newspaper) are prone to exhibit discrete cosine transform (DCT) artifacts such as ringing, smudging and macroblocking. M-JPEG-compressed video is also insensitive to motion complexity, i.e. variation over time. It is neither hindered by highly random motion (such as the water-surface turbulence in a large waterfall), nor helped by the absence of motion (such as static landscape shot by tripod), which are two opposite extremes commonly used to test interframe video formats.
For QuickTime formats, Apple has defined two types of coding: MJPEG-A and MJPEG-B. MJPEG-B no longer retains valid JPEG Interchange Files within it, hence it is not possible to take a frame into a JPEG file without slightly modifying the headers.
JPEG is inefficient, using more bits to deliver similar quality, compared to more modern formats (such as JPEG 2000 and H.264/MPEG-4 AVC). Since the development of the original JPEG standard in the early 1990s, technology improvements have been made not only to the JPEG format but to the interframe compression schemas possible as well.
Features
Motion JPEG is simple to implement because it uses a mature compression standard (JPEG) with well-developed libraries, and it is an intraframe method of compression.
It tolerates rapidly changing motion in the video stream, whereas compression schemes using interframe compression can often experience unacceptable quality loss when the video content changes significantly between each frame.
Minimal hardware is required because it is not computationally intensive.
Standardisation
Unlike the video formats specified in international standards such as MPEG-2 and the format specified in the JPEG still-picture coding standard, there is no document that defines a single exact format that is universally recognized as a complete specification of “Motion JPEG” for use in all contexts. This raises compatibility concerns about file outputs from different manufacturers. However, each particular file format usually has some standard on how M-JPEG is encoded. For example, Microsoft documents their standard format to store M-JPEG in AVI files, Apple documents how M-JPEG is stored in QuickTime files, RFC 2435 describes how M-JPEG is implemented in an RTP stream, and an M-JPEG CodecID is planned for the Matroska file format.