[MPlayer-users] Question about crop, scale, aspect ratio, multiple of 16

[nick]

Hi,

I'm trying to convert my Kill Bill 2 dvd (PAL) to avi. I've read the 
encoding-tips, chapter 7 of the Mplayer documentation and peices of the 
man page., but there are some thing that I don't understand:

1. It's is stated that the resolution(height/width) you choose to encode 
a movie should both be a multiple of 16. Must I use this rule when 
cropping the movie, or can I also crop the movie as follows:

... -vf crop=720:428:0:74

These crop values are suggested by cropdetect and cut away the bars 
prefectly.  Is it a problem that 428 is not a multiple of 16?

2. I have a hard time understanding what scaling actually is/does. I 
understand that the croped resolution should be scaled to get a bpp 
value larger that 0.20. Now, when I run the following command, just as a 
test:

mplayer -dvd-device VIDEO_TS dvd://5 -vf crop=720:428:0:74,scale=720:200

mplayer gives the following output:

Movie-Aspect is 1.78:1 - prescaling to correct movie aspect.
SwScaler: reducing / aligning filtersize 1 -> 4
SwScaler: reducing / aligning filtersize 1 -> 4
SwScaler: reducing / aligning filtersize 10 -> 9
SwScaler: reducing / aligning filtersize 10 -> 9

SwScaler: BICUBIC scaler, from Planar YV12 to Planar YV12 using MMX2
VO: [xv] 720x200 => 720x300 Planar YV12

The first thing I don't understand is why the Movie-Aspect says 1.78:1. 
When I look at the back cover of the dvd, is says Ratio 2.35:1.

The next part "prescaling to correct movie aspect". What is Mplayer 
doing here? Scaling the croped resolution with the 1.78:1 aspect ratio?
Scaling the croped resolution with the 2.35:1 aspect ratio?
Or is Mplayer rescaling the  scale parameters I defined, namely 720:200?
Or perhaps something else?

3. If the "multiple of 16" rule aplies to scaling, how can I get an 
resolution that has those specifications. Since Mplayer automatically 
adjusts the scaled resolutions accoring to the aspect ratio?

4. How does the autoaspect parameter work?
Should I when scaling try to keep as close to 2.35:1 as possible, or can 
I just use autoaspect in the chain to fix the aspect ratio?

Kind Regards,
Nick