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|Full name||Motion JPEG Video Codec|
Bitstream encoding for video in which each frame [or field?] is compressed using the JPEG still-image compression algorithm. Taken as a sequence, the series of frames represent the source video. MJPEG bitstreams are often wrapped in AVI files where they carry the Four-Character Code (FOURCC) MJPG. MJPEG bitstreams may also be managed or wrapped in other ways.
Avery Lee, writing in the rec.video.desktop newsgroup in 2001, commented that "MJPEG, or at least the MJPEG in AVIs having the MJPG fourcc, is restricted JPEG with a fixed -- and *omitted* -- Huffman table. The JPEG must be YCbCr colorspace, it must be 4:2:2, and it must use basic Huffman encoding, not arithmetic or progressive. . . . You can indeed extract the MJPEG frames and decode them with a regular JPEG decoder, but you have to prepend the DHT segment to them, or else the decoder won't have any idea how to decompress the data. The exact table necessary is given in the OpenDML spec.'
|Production phase||Generally a middle-state (video production) format; after editing, the bitstream is typically compressed in another encoding for end-user delivery.|
|Relationship to other formats|
|Used by||AVI_MJPEG, Audio Video Interleaved, MJPEG|
|Used by||QTV_MJPEG, QuickTime MJPEG|
|LC experience or existing holdings|
Difficult to describe. The underlying coding algorithms are well documented through the JPEG standards activity. However, additional information about use and wrappers is either informal or exists as proprietary implementations; see the comments in Description, above, and in some of the Useful references below.
None identified as of April 26, 2004. See Notes below.
Discussion in various web sites together with the availability of software tools suggests that there has been some use of MJPEG.
|Licensing and patents||
Apparently none, except as indicated for JPEG.
Depends upon algorithms and tools to read; will require sophistication to build tools. See also the comment in Description, above.
|Self-documentation||Not applicable; provided by wrapper formats.|
|Technical protection considerations||Not applicable; provided by wrapper formats.|
|Normal rendering||Not applicable|
|Clarity (high image resolution)||Very good to excellent, depending upon sampling (e.g., 4:2:2 as compared to 4:1:1, etc.), capture of both fields for each frame, the type and extent of compression, and the encoder used.|
|Functionality beyond normal rendering||Not applicable.|
|Filename extension||Not applicable.|
|Internet Media Type||Not applicable.|
|Magic numbers||Not applicable.|
||Used when this codec is wrapped in Microsoft file formats, e.g., AVI and ASF; see, for example the archived version of the Microsoft registry mounted by IANA.|
|General||Slight discussion of MJPEG in John McGowan's AVI Overview: Audio and Video Codecs (http://www.jmcgowan.com/avicodecs.html).|