[MPlayer-users] SwScaler: when?

[Mario Valle]

As usual I'm creating a movie from a set of JPEG or SGI images.
Strangely this time the movie have very visible blocking artifacts.
The only difference I can think of is the size of the frames: 768x576 and that the images 
are converted from PNG one. Another difference is in the colorspaces (are not the images 
created equal?).

I use pre3 with two pass encoding with lavcopts codec=msmpeg4v2:vbitrate=2592000:mbd=2

When the image is JPG the relevant part of the mencoder log is:

Writing AVI header...
[mjpeg @ 0x854dee0]mjpeg: JFIF header found (version: 1.1)
VDec: vo config request - 768 x 576 (preferred csp: Planar 444P)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
VDec: using Planar 444P as output csp (no 0)
Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
SwScaler: reducing / aligning filtersize 1 -> 4
SwScaler: reducing / aligning filtersize 9 -> 8
SwScaler: reducing / aligning filtersize 1 -> 1
SwScaler: reducing / aligning filtersize 9 -> 8

SwScaler: BICUBIC scaler, from Planar 444P to Planar YV12 using MMX2
videocodec: libavcodec (768x576 fourcc=3234504d [MP42])
High quality encoding selected (non real time)!

Instead with SGI images:

Writing AVI header...
VDec: vo config request - 768 x 576 (preferred csp: BGR 24-bit)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
VDec: using BGR 24-bit as output csp (no 0)
Movie-Aspect is undefined - no prescaling applied.
SwScaler: using unscaled BGR 24-bit -> Planar YV12 special converter
videocodec: libavcodec (768x576 fourcc=3234504d [MP42])
High quality encoding selected (non real time)!

For comparison here is the output for an image set that don't caused blocking artifacts:

Writing AVI header...
[mjpeg @ 0x854d480]mjpeg: JFIF header found (version: 1.1)
VDec: vo config request - 752 x 752 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 3)
Movie-Aspect is 1.00:1 - prescaling to correct movie aspect.
videocodec: libavcodec (752x752 fourcc=3234504d [MP42])
High quality encoding selected (non real time)!

Maybe the SwScaler action is a red herring, but is the only difference with the nice image.
Can you help to reduce my ignorance?
Thanks!
			mario

-- 
Ing. Mario Valle
Data Mining and Visualization Group         | http://www.cscs.ch/~mvalle
CSCS, Swiss Center for Scientific Computing | Tel:  +41 (91) 610.82.60
Via Cantonale, 6928 Manno, Switzerland      | Fax:  +41 (91) 610.82.82