[StainlessS]

All four sides.

GSCript("""
    Function Katie(clip c,int n,Int WKill,Int HKill) {
        c
        XMod = RT_ColorSpaceXMod  # Left and Right scan Width : eg 1 for RGB, 2 for YV12 & YUY2
        WKill = (WKill + XMod-1) / XMod * XMod  # Round UP  Will return WRONG SIZE and Error Alert of WKill not multiple of XMod.
        Lft=0   Rgt=0
        While(Lft+Rgt<WKill) {
            LAve=RT_AverageLuma(n=n,x=Lft,y=0,w=XMod,H=0)
            RAve=RT_AverageLuma(n=n,x=Width-XMod-Rgt,y=0,w=XMod,H=0)
            if(LAve<RAve)       {Lft = Lft + XMod}      # Lft is darker than Rgt
            else if(RAve<LAve)  {Rgt = Rgt + XMod}      # Rgt is darker than Lft
            else if(Lft<Rgt)    {Lft = Lft + XMod}      # Lft and Rgt same AveLuma AND Lft < Rgt
            else                {Rgt = Rgt + XMod}      # Lft and Rgt same AveLuma AND Rgt <= Lft            
        }
        YMod = RT_ColorSpaceYMod(Laced=False)   # Top and Bot Scan Height : eg 1 for RGB and YUY2, 2 for YV12
        HKill = (HKill + YMod-1) / YMod * YMod  # Round UP  Will return WRONG SIZE and Error Alert of HKill not multiple of YMod.
        Top=0   Bot=0
        While(Top+bot<HKill) {
            TAve=RT_AverageLuma(n=n,x=0,y=Top,w=0,H=YMod)
            BAve=RT_AverageLuma(n=n,x=0,y=Height-YMod-Bot,w=0,H=YMod)
            if(TAve<BAve)       {Top = Top + YMod}      # Top is darker than Bot
            else if(BAve<TAve)  {Bot = Bot + YMod}      # Bot is darker than Top
            else if(Top<Bot)    {Top = Top + YMod}      # Top and Bot same AveLuma AND Top < Bot
            else                {Bot = Bot + YMod}      # Top and Bot same AveLuma AND Bot <= Top             
        }
        Crop(Lft,Top,-Rgt,-Bot)
#       RT_DebugF("Lft=%d Rgt=%d : Top=%d Bot=%d W=%d H=%d",Lft,Rgt,Top,Bot,Width,Height,name="Katie: ")
        RT_Subtitle("Lft=%d Rgt=%d : Top=%d Bot=%d",Lft,Rgt,Top,Bot,Align=5)
        Return Last    
    }
""")

SCRIPT = "return Katie(ORG,current_frame,WKill,HKill)"   # We use ORG clip and simply discard the dummy clip (dont use it for anything)
#####################################
### Katie's Config Below
#Avisource("CabaretUncropped.avi")
mpeg2source("001.d2v")
bob(b=0,c=1)
selecteven()
#
WKILL = 16
HKILL = 0
#####################################
### Katie Hands off below
ORG = Last  # Uncropped source (clip2)
Dummy=Crop(WKILL,HKILL,0,0)                               # Scriptclip can ONLY return same size clip as arg, so we create dummy clip
Dummy.ScriptClip(SCRIPT,Args="ORG,WKILL,HKILL")    # Import ORG (full uncropped) clip into Scriptclip (req Grunt)
### Katie's Postscript
simpleresize(352,240)
###
Return Last

EDIT:

I... have no idea what that is or what I'm supposed to do with it...

Change

 
Avisource("CabaretUncropped.avi")

to whatever you want, it implements your suggested functionality.

WKILL and HKILL are total Width and Height pixels to crop. (Just try it and stop belly aching )

EDIT: Put RT_Stats, GScript and Grunt in Plugins directory, run script.