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1 : Isibaar 1.1 xvid vfw help
2 :     20/jan/02
3 :    
4 :     *** rate control ***
5 :    
6 :     xvid offers a number of different rate control modes
7 :    
8 :     - 1pass-cbr: constant-bitrate
9 :     use the bitrate slider to select the desired bitrate; refer to 'cbr constants' for advanced options. note: we actually use an average-bitrate algorithm, so the instaneous bitrate will fluxuate.
10 :    
11 :     - 1pass-quality
12 :     use the quality slider to select a desired quality percentile. the quality% is then used to calculate an average-quantizer.
13 :    
14 :     - 1pass-quantizer
15 :     force the codec to use a fixed quantizer for all frames. valid range: [1,31].
16 :    
17 :     - 2pass
18 :     a detailed explaination of 2pass can be found here: http://www.research.ibm.com/journal/rd/434/westerink.html
19 :     our implementation of two pass encoding requires three steps
20 :     1) 1stpass: collect compression statisics to a stats file.
21 :     2) process the stats using gordian knot, xihprom, etc.
22 :     3) 2ndpass: compress the video using both the original 1stpass stats file, and the normalized stats file.
23 :    
24 :    
25 :     *** encoder tuning ***
26 :    
27 :     - max keyframe interval
28 :     the maximum interval between keyframes.
29 :    
30 :     - motion search precision
31 :     controls the speed/quality of the motion search algorithm. range [0,6].
32 :     lower values are faster but reduce compressibility.
33 :     higher values are slower but increase compressibility.
34 :    
35 :     - quantization type
36 :     quantization is the process of removing detail. there are two types:
37 :     h.263: used by divx4.x and h263 encoders.
38 :     mpeg: used by the microsoft mpeg-4 encoder, mpeg-1/2.
39 :    
40 :     mpeg quantization gives sharper looking images, but can introduce grain/noise. while h.263 gives softer looking images, removes noise (but sometimes too much) and is slightly faster.
41 :    
42 :    
43 :     *** cbr constants ***
44 :    
45 :     these apply only to 1pass-cbr mode.
46 :    
47 :     - average peroid
48 :     the number of frames over which the average bitrate is maintained.
49 :    
50 :     - reaction peroid
51 :     (?) the number of frames inwhich we react to sudden change in bitrate.
52 :    
53 :     - up/down ratio
54 :     (?) a percentile representing how fast/much we react.
55 :    
56 :    
57 :     *** debug ***
58 :    
59 :     - min/max quantizer.
60 :     lets you limit the flexibility of the encoder.
61 :     a minquant=1 can sometimes cause problems with 1pass-cbr and 2pass.
62 :    
63 :     - luminance masking
64 :     enabled per-macroblock quantizer decision. very experimental
65 :    
66 :     - discard encoded bitstream on 1st-pass
67 :     by default xvid discards the compressed bitstream during the the 1st pass of a two pass encoding session. example: in windows you end up with an empty .avi file. if this box is unchecked the bitstream is kept.
68 :     note: the 1st compressed bitstream can large.
69 :    
70 :     this can be used to perform a 'fast 2pass' encoding.
71 :     1) perform 1st pass encoding of your source material with discard unchecked.
72 :     2) process the stats file
73 :     3) open the bitstream created in the first pass, and perform the 2nd pass on it.
74 :     note: there is some quality loss. judge it for yourself.
75 :    
76 :     - perform dummy 2nd-pass
77 :     this can be used to check the accuracy of your stats file processor/calculator. it instructs xvid to create a dummy/junk bitstream exactly to the size described in the processed stats file.
78 :    
79 :     *** cpu ***
80 :    
81 :     provides auto/manual control over cpu-feature optimizations.
82 :    
83 :    
84 :     *** about ***
85 :    
86 :     build timestamp, etc.

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