Dedicated Micros SD Range, Инструкция по установке и эксплуатации

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Dedicated Micros ©2007
SD Range
A video sequence of a scene consists of a number of pictures or frames. In a static scene, the initial
frame contains an image. If there is no movement in the scene, all subsequent frames will contain
the same data. MJPEG recording will record and compress each image individually.
MPEG-4 is used primarily to compress audio and visual (AV) digital data (moving images and
sound). MJPEG is an informal name for multimedia recording where each video frame is separately
compressed as a JPEG image.
If this redundancy were removed and only the changes in scene were recorded, it would be possible
to get a better compression ratio.
MPEG-4 recording uses a keyframe (I-Frame) to record the full scene, then uses the following
frames to record the differences between the I-Frame and each subsequent frame (P-Frames) i.e.
the difference between I-Frame and frame 1, then the difference between frame 1 and frame 2, etc.
These frames enable the true picture to be recorded but the time between I frames determines the
step back/forward interval that can be used.
The advantage of MPEG-4 recording is that, in static scenes, it requires less disk space to record a
time period than the equivalent JPEG recording. It is important to select an I-frame rate sufficient for
accurate recording whilst maintaining the lower recording requirement of MPEG-4. Note that I-frame
rates are auto set on the SD.
MPEG-4 is better suited to recording static scenes with little or no movement.
Motion JPEG (MJPEG) uses intraframe coding technology similar to the I-frame part of MPEG-
4, but does not use the P-Frame interframe prediction. This makes the degree of compression
capability independent of the amount of motion in the scene as each scene is recorded entirely. This
means that more storage space is required to record a given scene, but there is a lower processor
overhead, and each frame is an individual separate image.
MJPEG is better suited to recording high motion scenes, or scenes during an alarm state.
Note: Dedicated Micros recommends using MPEG4 as a background recording setting; switching
to MJPEG on event or alarm.