ADS Technologies USBAV-708 INSTANT VIDEOMPX, User Manual

Page: 45 / 116

The
Guide
45
Bi
tra
te
m
od
e
1-Pas
s,
Q
ual
ity
-ba
se
d
In 1-Pass quality-based mode the encoder will
output a working DivX video stream as it
receives the source video, similar to in 1-Pass
mode except that you specify the quality rather than the
target bitrate.
This mode is only accessible when profiles have been
disabled from the
Select Profile Wizard .
Quality is set by adjusting the
Quantizer control. As
described in Forward—Quantizers , the quantizer is the
method DivX uses to control the
accuracy of the image data it
stores. Lower quantizers relate
to higher quality, higher
quantizers to lower quality.
By fixing the quantizer you guarantee a consistent quality throughout your entire
video file by ensuring the encoder stores the image data for each frame with a
consistent accuracy. However, when you fix the quantizer it is not possible to set
or predict the bitrate and hence file size because the encoder will always spend
as many bits as are required to encode each frame at the given quantizer.
Quality-based mode is ideal when you need to be assured of a fixed quality
regardless of file size, and particularly when capturing from live or analogue
sources that you intend to later re-compress.
Note that even when the quantizer is 1 and the display reads 100% quality the
encoded video will not be identical to the source. DivX is not a lossless codec,
and there will always be some degradation from the source video regardless of
the combination of settings that you choose.
After running a 1-Pass quality-based encoding your DivX file can be viewed
immediately.
QUICK GUIDE
1-Pass, Quality-based