[MEncoder-users] bad numbers of psnr for xvid in mac

[Mauricio Alvarez]

Hi

I am using mencoder for coding raw YUV files into mpeg-4 using xvid on a
ppc970 mac os x machine

- first i put the yuv files into an avi using ffmpeg
$ffmpeg -s 720x576 -t 4 -i yuv/576p25_blue_sky.yuv -vcodec copy -r 25
test.avi
that's OK

- second, I use mencoder to encode the video using xvid
$mencoder test.avi -o test_xvid.mp4 -ovc xvid -xvidencopts
fixed_quant=3:max_bframes=2:qpel:psnr:debug=3

that's also OK, but when I look at the PSNR numbers something is wrong
because it says that the luna average PSNR is 16.76. This is not true
because I see the video and the (perceptual) quality is really high.

When I look in the psr_xx.log file generated by xvid I see that b-frames
are responsible for this (not true) low PSNR.

     0,  3,  71027, 44.16, 43.76, 44.49, 44.14 I
     1,  5,   2500, 16.42, 24.74, 21.70, 17.72 B
     2,  5,   2108, 15.00, 23.17, 23.48, 16.46 B
     3,  3,  19891, 42.93, 42.76, 43.99, 43.06 P
     ...

Any idea about how to get the correct psnr?

Thanks
Mauricio

p.d. the complete output of mencoder

$ mencoder test.avi -o test_xvid.mp4 -ovc xvid -xvidencopts
fixed_quant=3:max_bframes=2:qpel:psnr:debug=3
MEncoder dev-CVS-050512-13:17-3.3 (C) 2000-2005 MPlayer Team
AltiVec found
CPU: PowerPC
File not found: 'frameno.avi'
Failed to open frameno.avi
success: format: 0  data: 0x0 - 0x3b55370
AVI file format detected.
AVI_NI: No audio stream found -> no sound.
AVI: No audio stream found -> no sound.
VIDEO:  [024I]  720x576  24bpp  25.000 fps  124416.0 kbps (15187.5 kbyte/s)
[V] filefmt:3  fourcc:0x30323449  size:720x576  fps:25.00  ftime:=0.0400
xvid: using library version 1.1.-125 (build xvid-1.1.0-beta2)
Opening video filter: [expand osd=1]
Expand: -1 x -1, -1 ; -1  (-1=autodetect) osd: 1
==========================================================================
Opening video decoder: [raw] RAW Uncompressed Video
VDec: vo config request - 720 x 576 (preferred csp: Planar I420)
VDec: using Planar I420 as output csp (no 0)
Movie-Aspect is undefined - no prescaling applied.
videocodec: XviD (720x576 fourcc=44495658 [DIVX])
xvid: par=0/0 (vga11), displayed=720x576, sampled=720x576
xvid: Fixed Quant Rate Control -- quantizer=3/1=3.00
Selected video codec: [rawi420] vfm:raw (RAW I420)
==========================================================================
Writing AVI header...
ODML: vprp aspect is 16384:13107.
ODML: vprp aspect is 16384:13107.
Pos:   3.9s    100f (98%)   4fps Trem:   0min   1mb  A-V:0.000 [2271:0]
Flushing video frames

Writing AVI index...
Fixing AVI header...
ODML: vprp aspect is 16384:13107.

Video stream: 2237.810 kbit/s  (279726 bps)  size: 1118905 bytes  4.000
secs  100 frames
The value 99.99dB is a special value and represents the upper range limit
xvid:     Min PSNR y : 13.66 dB, u : 22.83 dB, v : 22.68 dB, in frame 86
xvid: Average PSNR y : 16.76 dB, u : 24.94 dB, v : 24.72 dB, for 99 frames
xvid:     Max PSNR y : 44.16 dB, u : 43.76 dB, v : 44.49 dB, in frame 0

$ more psnr_165454.log
     0,  3,  71027, 44.16, 43.76, 44.49, 44.14 I
     1,  5,   2500, 16.42, 24.74, 21.70, 17.72 B
     2,  5,   2108, 15.00, 23.17, 23.48, 16.46 B
     3,  3,  19891, 42.93, 42.76, 43.99, 43.06 P
     4,  5,   2615, 15.40, 23.21, 23.35, 16.82 B
     5,  5,   1960, 14.59, 22.97, 23.21, 16.06 B
     6,  3,  21485, 42.91, 42.67, 43.94, 43.03 P
     7,  5,   2201, 14.75, 24.48, 21.33, 16.17 B
     8,  5,   1812, 14.06, 22.98, 23.06, 15.56 B
     9,  3,  21578, 42.83, 42.55, 43.75, 42.92 P
    10,  5,   2402, 16.75, 23.33, 23.91, 18.08 B
     ...