[Ffmpeg-devel] Degradation of x264 encoding in my build of ffmpeg

[Laine Lee]

I'm using Mac OS X 10.4.3 and my own build of the most recent version of
ffmpeg (from CVS today). I'm trying to find out why my build of ffmpeg
yields deprecated results as compared to the results I get when I use the
build included with ffmpegX to feed a an encoding command to x264. The
command encodes a .VOB file to a .mp4 file. When I use the following
commands to create h.264 video output from ffmpeg, the output from my build
yields a video whose deficiency is mainly visible in that the picture rolls
horizontally and increasingly migrates toward the bottom of the frame
leaving an area of green at the top of the frame.

The command  is this:

'/Users/llee/Library/Application Support/No Frills DVD2iPod/ffmpeg' -i
'/Users/llee/Desktop/No Frills DVD2iPod/Goblin.VOB' -an -f yuv4mpegpipe
-croptop 0 -cropbottom 0 -cropleft 0 -cropright 0 -s 320x176 -r 29.97 - |
'/Users/llee/Library/Application Support/No Frills DVD2iPod/x264' -A i4x4
--no-cabac -b 0 --qpmin 10 --qpmax 51 -B 215 --me hex --threads 2 --level 13
--fps 29.97 -o 
'/private/var/tmp/folders.501/TemporaryItems/1/Goblin.vid.mp4' - 320x176

The results generated by x.264 when the command is passed by the ffmpegX
version of the executable that didn't deprecate quality are these:

frame=   99 q=0.0 Lsize=    8168kB time=3.3 bitrate=20254.9kbits/s
video:0kB audio:0kB global headers:0kB muxing overhead inf%
x264 [info]: slice I:1     Avg QP:21.00  size: 15041  PSNR Mean Y:42.01
U:44.36 V:44.34 Avg:42.66 Global:42.66
x264 [info]: slice P:98    Avg QP:29.84  size:   829  PSNR Mean Y:34.34
U:39.57 V:39.13 Avg:35.45 Global:35.37
x264 [info]: mb I  I16..4:  7.3%  0.0% 92.7%
x264 [info]: mb P  I16..4:  0.1%  0.0%  0.4%  P16..4: 52.7%  0.0%  0.0%
0.0%  0.0%    skip:46.9%
x264 [info]: final ratefactor: 27.54
x264 [info]: PSNR Mean Y:34.417 U:39.620 V:39.180 Avg:35.525 Global:35.409
kb/s:233.21

The results generated by x.264 when the command is passed by my build of the
executable that deprecated quality are these:

frame=   99 q=0.0 Lsize=    8168kB time=3.3 bitrate=20256.5kbits/s
video:0kB audio:0kB global headers:0kB muxing overhead inf%
x264 [info]: slice I:1     Avg QP:21.00  size: 15163  PSNR Mean Y:41.98
U:44.39 V:44.38 Avg:42.65 Global:42.65
x264 [info]: slice P:98    Avg QP:34.57  size:   823  PSNR Mean Y:31.17
U:34.83 V:34.53 Avg:32.03 Global:31.91
x264 [info]: mb I  I16..4:  3.2%  0.0% 96.8%
x264 [info]: mb P  I16..4:  7.6%  0.0%  1.5%  P16..4: 69.6%  0.0%  0.0%
0.0%  0.0%    skip:21.4%
x264 [info]: final ratefactor: 31.93
x264 [info]: PSNR Mean Y:31.274 U:34.929 V:34.629 Avg:32.139 Global:31.955
kb/s:231.94

My build of ffmpeg uses precisely the same configuration options indicated
in the version of ffmpeg included with ffmpegX. Please tell me what might be
causing the difference in output that results in the degradation. Thanks.

-- 
Laine Lee 
Visit the Mac Shack at http://moss.utsa.edu
My Homepage: http://lonestar.utsa.edu/llee