[XviD-devel] On the compression ratio of xvidcore
lingan
linganmm at gmail.com
Sat Nov 22 15:42:04 CET 2008
Hello, dear:
I'm studying to use xvidcore to encode yuv images into mpeg4, But
I find the compression ratio I get is quite low. For example, I use
the following command to encode a yuv file :
p9322 at wllab1:~/program863/xvidcore-1.1.3/examples$ ./xvid_encraw -i
coastguard_cif.yuv -type 0 -w 352 -h 288 -frames 1000 -o
coastguard.mpeg4 -max_key_interval 10
then :
p9322 at wllab1:~/program863/xvidcore-1.1.3/examples$ ls -lh coastguard*
-rw-r--r-- 1 p9322 p9322 44M 2008-10-31 17:35 coastguard_cif.yuv
-rw-r--r-- 1 p9322 p9322 6.1M 2008-11-21 22:35 coastguard.mpeg4
you see? the compression ratio is only about 7.
this is part of the encoding output info:
xvid_encraw - raw mpeg4 bitstream encoder written by Christoph Lampert
2002-2003
0: key=2, time= 21, len= 36006 | type=I, quant= 2, len= 36006
1: key=0, time= 24, len= 19250 | type=P, quant= 2, len= 19250
2: key=0, time= 28, len= 20667 | type=P, quant= 2, len= 20667
3: key=0, time= 23, len= 20431 | type=P, quant= 2, len= 20431
4: key=0, time= 29, len= 22397 | type=P, quant= 2, len= 22397
5: key=0, time= 23, len= 20005 | type=P, quant= 2, len= 20005
6: key=0, time= 28, len= 21632 | type=P, quant= 2, len= 21632
7: key=0, time= 27, len= 21329 | type=P, quant= 2, len= 21329
8: key=0, time= 23, len= 20117 | type=P, quant= 2, len= 20117
9: key=0, time= 24, len= 20940 | type=P, quant= 2, len= 20940
10: key=2, time= 11, len= 36691 | type=I, quant= 2, len= 36691
11: key=0, time= 34, len= 18852 | type=P, quant= 2, len= 18852
12: key=0, time= 35, len= 21458 | type=P, quant= 2, len= 21458
13: key=0, time= 34, len= 20337 | type=P, quant= 2, len= 20337
the resulted P frames are not much larger than I frames.
Then I use xvidcore to encode the webcam stream, the output info is as
follows:
frame: key=2,len= 14441 | type=^@, quant= 0, stat_len= 0
frame: key=0,len= 0 | type=^@, quant= 0, stat_len= 0
frame: key=0,len= 8593 | type=I, quant= 2, stat_len= 14441
frame: key=0,len= 2676 | type=B, quant= 4, stat_len= 2676
frame: key=2,len= 14325 | type=P, quant= 2, stat_len= 8593
frame: key=0,len= 8105 | type=I, quant= 2, stat_len= 14325
frame: key=0,len= 2813 | type=B, quant= 4, stat_len= 2813
frame: key=2,len= 14290 | type=P, quant= 2, stat_len= 8105
frame: key=0,len= 6932 | type=I, quant= 2, stat_len= 14290
......
The second column is the length of coded frame. My webcam is 320x240,
so the compression ratio is about 320x240x3/10000=23. And strangely,
the volume of P frames is even larger than I frames sometimes.
It's said that mpeg4 can achieve at most 400 compression ratio.
Generally, it can achieve 6,70 compression ratio easily. But why the
CR I get is so small ? Any suggestions?
The version is xvidcore-1.1.3, and the OS is debian linux-2.6.21.7.
Thank you very much!!
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