Greetings -
I was curious about how -K and the 3 choices for quantization
matrices (default, tmpgenc and kvcd) behaved with different values
of '-q'.
Source material was a 12962 (NTSC) frame (7m12s) cartoon captured
from laserdisc using a S-Video cable to a Canopus ADVC100 analog->DV
converter.
The basic script used was:
--------------
#!/bin/sh
# Takes two arguments: -q and -K:
# Example:
# ./dvd.sh 4 0.1
smil2yuv -i 2 redhotridinghood.dv | \
y4mshift -b 12,4,696,476 | \
y4mscaler -O chromass=420_MPEG2 | \
bfr -b 10m | \
mpeg2enc -f 8 -M 2 -q $1 -K $2 -o foo.m2v
---------------
The default bitrate used by mpeg2enc for -f 8 is 7500.
The 4:1:1 (NTSC DV) to 4:2:0 conversion was done in 'y4mscaler',
thus the use of "smil2yuv -i 2" (y4mscaler seems to produce better
output than doing the conversion in smil2yuv+libdv). Other than that
no filtering/manipulation of the data was done.
Audio was prepared manually ahead of time with the usual 'smil2wav'
and toolame.
The I/P/B frame sizes and average bitrate reported in the tables below
were extracted via perl scripts from the output of 'mplex -f 8 -o
/dev/null foo.m2v foo.mp2".
The bitrate is in kbits/sec (1000) and is the number reported by
mplex in the 'Average bit-rate' field divided by 1000.
I/P/B frame sizes are in bytes.
The 'ratio' column is the current -K's average bitrate divided by the
avearage bitrate for '-K default' within a -q table.
There were 5 values of -q used ranging from a quite low (high quality)
of 4 and up to and including 9 (8 is the default used by mpeg2enc for
DVD (-f 8)). For each -q the -K parameter took on one of the three
choices: default (standard MPEG-2), tmpgenc, kvcd.
The main observation is that the amount of influence -K has
increases as the quality is lowered (-q increases). At a high quality
setting (-q 4) changing -K has little effect because the encoder is
up against the bitrate limit, while at a slightly lower quality
setting (-q 6) it can be seen that altering -K has a much larger
effect and at -q 9 the difference between 'default' and the other
two choices is quite substantial
Enjoy.
Cheers,
Steven Schultz
q -K I P B Rate Ratio
- - - - - ---- -----
4 default 33898 32730 29832 7405.2 1.000
4 tmpgenc 45287 34523 27975 7412.0 1.001
4 kvcd 55975 35575 26394 7403.2 1.000
5 default 33133 32414 29840 7373.6 1.000
5 tmpgenc 43874 33855 27792 7316.4 0.992
5 kvcd 54730 34220 25401 7137.6 0.968
6 default 32515 32082 29625 7308.0 1.000
6 tmpgenc 43002 32463 26204 6960.4 0.952
6 kvcd 51634 29877 21542 6194.0 0.848
7 default 31817 31347 28767 7112.8 1.000
7 tmpgenc 41678 28127 22235 6028.4 0.848
7 kvcd 48115 25323 17916 5267.2 0.741
8 default 29736 30762 28838 7052.4 1.000
8 tmpgenc 35126 24703 19886 5327.6 0.755
8 kvcd 39646 22008 16215 4644.0 0.658
9 default 28059 21852 19083 4900.4 1.000
9 tmpgenc 28665 16317 12707 3540.4 0.722
9 kvcd 34260 15508 11058 3318.0 0.677
