MPEG2 vs. MJPEG Compression

[ThomasG]

I am very new to digital video editing and would like some clarification. With the new Marvel using MPEG2 compression instead of MJPEG, it makes me ask: In general, what are the advantages/disadvantages of MPEG2?
What are the advantages/disadvantages of MJPEG? Any help would be greatly appreciated.

[Hulk]

I'm pretty new to this as well but I'm going to offer my comments anyway

MJPEG is a method of compressing video by compression each frame of the video using the familiar JPEG compression scheme. The greater the compression ratio the smaller the resulting file but the worse the quality. Same as when you compress tiff images to jpeg's.

MPEG II is a form of compression that not only compresses individual frames but also uses a more advanced form of compression referred to as temporal compression. Basically it compresses the first of a series of frames like the MJPEG format does but then it predicts and interpolates frames until the next I frame. Since it is often the case that not much changes from one frame to the next, it's often more beneficial to just save the changes in each frame. That's why it's referred to as a temporal compression scheme, it compresses interframe (between frame) and intraframe (within frame). The program uses a motion compensation method to predict the location of moving objects from frame to frame. The more advanced the motion compensation the better the results. The cost is higher processing required.

MJPEG is less processor intensive and easier to edit since every frame is actually on the hard drive. MPEG II will generally be of higher quality assuming the same data rate but will require much more processing power since all but the "I" frames need to be "generated." This also makes editing more difficult.

I think that Matrox is going with MPEG II because processing power has become so cheap. A 800MHz chip can be had for well under $300 and is sufficient for high quality MPEG II compression. When the fastest chip was a PII400 or so it made sense to include hard MJPEG encoding with the Marvel series.

Mark

[ThomasG]

Thank you. That is very helpful.

Thomas