[x264-devel] Bug: horizontal stripes on PPC with Altivec since snapshot 20081125

[Josef Drexler]

Since the version in snapshot x264-snapshot-20081125-2245.tar.bz2,  
x264 encodes show semi-random, clearly visible horizontal stripes of  
what looks like excessive color saturation, particularly in dark  
areas surrounded by light areas. Versions up to and including x264- 
snapshot-20081124-2245.tar.bz2 do not exhibit this problem.

Platform: PPC G4 with Altivec, OS X 10.4.11
Compiler: gcc 4.0.1 shipped with OS X

I encoded the video using mencoder r28135.

mencoder x264 options:
bitrate=900:frameref=6:bframes=3:direct_pred=auto:b_pyramid:weight_b:me= 
umh:mixed_refs:subq=6
additionally pass=1:turbo=2 and pass=2 for the two passes

There are a few compile warnings, but they show up in both the  
versions that work and those that exhibit the bug. Still, in case  
they matter here they are:
encoder/macroblock.c: In function 'x264_macroblock_probe_skip':
encoder/macroblock.c:724: warning: 'mvp[0]' may be used uninitialized  
in this function
encoder/macroblock.c:724: warning: 'mvp[1]' may be used uninitialized  
in this function
common/ppc/pixel.c: In function 'pixel_satd_8x4_altivec':
common/ppc/pixel.c:245: warning: 'temp4v' is used uninitialized in  
this function
common/ppc/pixel.c:245: warning: 'temp5v' is used uninitialized in  
this function
common/ppc/pixel.c:245: warning: 'temp6v' is used uninitialized in  
this function
common/ppc/pixel.c:245: warning: 'temp7v' is used uninitialized in  
this function