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Video Formats and Digital Video
Compression Ratio and Recording Times
Wavelet Compression
Audio Compression
Rev 1.00
decompressed. Obviously this is not suitable for some types of data, such as numerical
data or text, but nonreversible compression algorithms that have been especially designed
for video images create small changes in the image that do not significantly alter the overall
look of the picture. These small changes are called digital artifacts.
How noticeable digital artifacts are depends on the amount and type of compression. By
carefully tailoring compression, the digital artifacts can be reduced to a virtually
unnoticeable level. The HRDV16/8 uses Wavelet compression which produces images that
do not show any obvious digital artifacts. Other compression schemes (for example, JPEG
compression) will show digital artifacts such as block artifacts or 'stair stepping' where the
edge of a diagonal line has a slightly jagged edge.
The HRDV16/8 uses compression ratios that vary from 10:1 to 35:1, in increments of 5. A
10:1 compression ratio reduces the throughput for NTSC resolution to approximately 2
MBs. Most hard drives have no problem operating at this throughput rate. However, at this
rate a 9 GB hard drive would be full in approximately one hour. To select a compression
ratio, you must balance the desired picture quality against the hard drive storage available.
The HRDV16/8 uses Wavelet video compression to reduce the size of recorded video files.
This advanced method of compression maintains a high image quality level, while
achieving high compression ratios.
Wavelet compression features:
•
Eliminates the block artifacts seen in Discrete Cosine Transform (DCT) compression
schemes such as JPEG and MPEG compression. At very high compression ratios
images compressed with Wavelet compression become 'softer' with less detail,
saturation and contrast, rather than an image with obvious digital artifacts.
•
Uses a simple motion detection algorithm which makes it ideal for CCTV applications
You can change the compression used by your system in the Setup mode (see
Recording
Setup, page 61,
and
Pre-Event Recording
Setup, page 83).
CD-quality stereo sound uses an audio sampling rate of 44100 samples per second. This
requires a data transfer rate of 172 kBs. For timelapse audio recording the HRDV16/8 uses
True Speech compression—a speech compression mode that uses only 1.04 kBs. The
audio data can be played back in sync with the video image data. If you do not need sound
recorded with your video you may choose not to record from the audio output.
Motion Event Recording
Setup, page 77,
204
Timelapse
Alarm
Setup, page 35,
Document 900.0261
04/05
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