The new Canon EOS-1D X has two video compression options, intraframe ALL-I and interframe IPB. So just what are the differences between the two?
First it’s important to note that ALL-I is in-TRA-frame and IPB is in-TER-frame. Easy to over look that slight spelling difference.
The edit friendly intraframe ALl-I only compresses information in the current frame and does not use any temporal processing. Meaning the compression algorithm is not doing any type of comparison between frames. Think of it as a continuous series of still images that are each individually compressed. Intraframe compression is easier to edit with because the computer does not need to interpolate any data between each frame. With intraframe ALL-I, quality is higher, file size is larger, and the video files will use less computer processing power.
The file size conscious intraframe IPB uses some complex algorithms to compare neighboring frames and tries to find similarities from one frame to another. It can then achieve higher compression rates because it deals less with the parts of the image that stay the same from frame to frame. With interframe IPB, quality is lower (although Canon says not by much), file size is smaller, and the video files will use more computer processing power.
UPDATE: Canon has announced the 5D Mark III which also offers intraframe ALL-I and interframe IPB compression. Read more about the Canon 5D Mark III