ADS Technologies USBAV-708 INSTANT VIDEOMPX, Руководство пользователя

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The
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In Multipass mode you are required to run the
video through the encoder two or more times.
On every successive pass the video must be
identical to that which you used in your first pass.
As discussed in “
Bitrate mode—What is the bitrate? ”, DivX uses a rate control
algorithm to vary the bitrate throughout the video in order to achieve a consistent
quality while targeting the specified average bitrate. To do this effectively DivX
has to be able to examine the entire video in order to determine where bandwidth
should be allocated before it spends any bits at all.
Multipass, 1st pass
In 1-Pass mode the rate control strategy is not
optimal because the encoder has no foresight
into the content of the video. Therefore, in order
to meet the specified bitrate the rate control
must make extreme changes to the bitrate
based upon the short term history as video is
received.
Multipass mode is designed to avoid this
extremism by allowing the encoder to first
analyze the entire video before encoding it. This
analysis is performed in
Multipass 1st Pass mode, and during the first
pass no actual video output is written (if you attempt to play your file
after running a 1st pass you will see no video).
In Multipass 1st pass mode the encoder writes its
analysis to the log file specified in the
Multipass
encoding options area of the configuration dialogue.
Lets take a brief look at the log contents and what they mean:
QUICK GUIDE
Multipass
##map version 8
nframes 5837
timescale 30000
passes 1
seq deltaT type total_bits motion_complexity texture_complexity modulation
0 0 I 7712 0.000000 0.251141 1.000000
2 2400 P 2952 0.035268 0.011100 1.000000
1 -1200 B 1144 0.015206 0.000000 1.000000
4 3600 P 6984 0.067981 0.069732 1.000000
3 -1200 B 2216 0.029374 0.000000 1.000000
6 3600 P 8160 0.079010 0.082583 1.000000
5 -1200 B 2264 0.029773 0.000745 1.000000
8 3600 P 14176 0.083506 0.294013 1.000000