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C695M-B (11/03) 43
MPEG STRUCTURE AND FRAME OPERATIONS
There is a difference between the displayed time index during step-forward and step-backward operations. This results from the
compression techniques used in MPEG.
When video is recorded, the DX3100 does not store every piece of information contained in each video frame. Otherwise, the file would
be too large. Instead, the unit stores all of the information in some video frames. These complete frames are called I-frames.
The unit also creates P-frames between successive I-frames. P-frames contain only the changes since the previous I-frame or P-frame.
Because of this construction, a step-forward command displays video on a frame-by-frame basis. However, this is not possible when
stepping backward. The step-backward command causes jumps from one I-frame backward to the previous I-frame because P-frames do
not contain reverse direction changes.
Also, if you pause forward video playback and it stops between I-frames, the video will skip to the next I-frame when playback is
resumed. To view the skipped P-frames, rewind past a couple of I-frames and play the video forward again.