[XviD-devel] RE: possible vfw YV12 stride bug

[Klaus Post (KPO)]

Hi!
 
(( I somehow seem to have been disconnected from the mailinglist, but I
found this in the archive. Now also a plain text version. Sorry for the
trouble ;) )
 
>>In compress(), codec.c, stride is being computed as:
 
 
- Yes, it is wrong!
 
- In general, VFW stride is always rounded up to nearest 4-byte
boundary. The first line is ok:
 
frame.input.stride[0] = (((icc->lpbiInput->biWidth *
icc->lpbiInput->biBitCount) + 31) & ~31) >> 3;
 
However - YV12 is special.
 
Y-Plane is also 4-byte aligned, so it should be:
 
if (frame.input.csp == XVID_CSP_I420 || frame.input.csp ==
XVID_CSP_YV12)                                       
                      frame.input.stride[0] = (((icc->lpbiInput->biWidth
+ 3) >> 2;
 
UV planes are _always_ HALF of the Y-plane, so U&V planes are only 2byte
aligned.
 
This is at least my experience from AviSynth YV12 implementation.
 
 
Klaus Post, Producer