[StainlessS]

Something like this (writing frames to reject in realtime pass, as likely fewer than writing all selected frames)

Avisource("D:\V\StarWars.avi").Trim(0,10000)

GSCript("""
    Function Test(Clip c, int n,int v1,Float th,String File,Bool Show) {
        c
        mx   = RT_YPlaneMax(n,Threshold=th)
        if(mx < v1) {
            RT_WriteFile(File,"%d",n,Append=True)                       # Write unwanted frames (fewer than wanted)
            (Show) ? RT_SubTitle("%d] mx=%d - DELETING",n,mx) : NOP
        } else {(Show) ? RT_SubTitle("%d] mx=%d",n,mx) : NOP}
        Return Last    
    }    
""")

OutFile = "Frames.txt"
RT_FileDelete(OutFile)      # Delete existing  
V1 = 18                     # Was not deleteing anything for me at 16
th = 0.2                    # Avoid 0.2% of noise above v1
Show=True                   # CHANGE to FALSE when happy with numbers
SSS = "Test(current_frame,V1,th,OutFile,Show)"
ARGS= "v1,th,OutFile,Show"
ScriptClip(SSS,args=ARGS,after_frame=True)

(!Show)                 ? ForceProcessAVI()         : NOP               # Force Pass 1 (From TWriteAVI v2.0) ie force writing of frames file    
(!Show&&Exist(OutFile)) ? RejectRanges(Cmd=Outfile) : NOP               # If Outfile does not exist, then none to Reject.

Return last    
                            
Function RejectRanges(clip c,String "SCmd",String "Cmd",Bool "TrimAudio",Float "FadeMS") {
    # RejectRanges() by StainlessS. Required:- FrameSel, Prune, RT_Stats
    # Wrapper to delete frames/ranges along with audio, can supply frames/ranges in SCmd string And/Or Cmd file.
    #   The wrapper makes for easier usage of Prune() which supports up to 256 input clips, but requires a clip index,
    #   eg '3, 100,200' would specify clip 3, range 100 to 200. The wrapper does away with the necessity for the clip index as we
    #   are only using a single clip here. Prune also does not have a 'reject' arg to delete specified frames rather than select them,
    #   this wrapper also converts a list of frames to delete into a list of frames to select so that we can use Prune and its audio
    #   capability.
    #
    # SCmd: Frames/Ranges specified in String (Frames/Ranges either Chr(10) or ';' separated, infix ',' specifies range, eg 'start,end').
    # Cmd:  Frames/Ranges specified in file (one frame/range per line, comments also allowed, see FrameSel for Further info).
    # TrimAudio:
    #   True(default), deletes audio belonging to deleted frames
    #   False, returns original audio, probably out of sync.
    # FadeMS: (default 1.0 millisec). Linear Audio Fade duration at splices when TrimAudio==true, 0 = dont fade (might result in audio 'clicks/cracks').
    c
    TrimAudio=Default(TrimAudio,True)   # default true trims audio, false returns original audio (audiodubbed, as Framesel returns no audio)
    FadeMS=Float(Default(FadeMS,1.0))   # 1 millisecond linear fadeout/fadein at splices
    PruneCmd = (TrimAudio) ? "~Prune_"+RT_LocalTimeString+".txt" : ""
    (!TrimAudio)
        \ ? FrameSel(scmd=SCmd,cmd=Cmd,reject=true)
        \ : FrameSel_CmdReWrite(PruneCmd,scmd=SCmd,cmd=Cmd,reject=true,Prune=True,range=true)
    (TrimAudio) ? Prune(Cmd=PruneCmd,FadeIn=True,FadeSplice=True,FadeOut=True,Fade=FadeMS) : NOP
    # If TrimAudio==true then delete Prune temp file, Else restore original Audio to the now audio-less clip
    (TrimAudio)
        \ ? RT_FileDelete(PruneCmd)
        \ : (c.HasAudio) ? AudioDub(c) : NOP
    Return Last
}

and to view rejected frames only

Avisource("D:\V\StarWars.avi").Trim(0,10000)

    OutFile = "Frames.txt"
    SelectRanges(Cmd=Outfile)  # or change to RejectRanges to view kept after 1st pass script    
    Return last    
    
# From Prune [req FrameSel]            
Function SelectRanges(clip c,String "SCmd",String "Cmd",Bool "TrimAudio",Float "FadeMS",Bool "Ordered") {
    # SelectRanges() by StainlessS. Required:- FrameSel, Prune, RT_Stats
    # Wrapper to Select frames/ranges along with audio, can supply frames/ranges in SCmd string And/Or Cmd file.
    #   The wrapper makes for easier usage of Prune() which supports up to 256 input clips, but requires a clip index,
    #   eg '3, 100,200' would specify clip 3, range 100 to 200. The wrapper does away with the necessity for the clip index as we
    #   are only using a single clip here.
    #
    # SCmd: Frames/Ranges specified in String (Frames/Ranges either Chr(10) or ';' separated, infix ',' specifies range, eg 'start,end').
    # Cmd:  Frames/Ranges specified in file (one frame/range per line, comments allowed, see FrameSel for Further info).
    #  *** NOTE ***, If both Cmd and SCmd supplied AND Ordered == False, then will process Cmd file and then SCmd string afterwards, ie
    #    Will select ranges in Cmd file and in order specified (rather than auto ordering ranges) and then append ranges specified in
    #    SCmd string (and in order specified).
    # TrimAudio:
    #   True(default), selects audio belonging to selected frames/ranges
    #   False, returns original audio, probably out of sync (maybe totally out of whack if Ordered == false and selected ranges out of order).
    # FadeMS: (default 1.0 millisec). Linear Audio Fade duration at splices when TrimAudio==true, 0 = dont fade (might result in audio 'clicks/cracks').
    # Ordered:
    #   True(default), all frames/ranges are returned in sequencial order. Any frame specified more than once will return only 1 instance.
    #   False, All frames/Ranges are returned in specified order, Cmd processed first and then SCmd. Frames/ranges specified more than once
    #     will return multiple instances. Allows out-of-order trimming of clip, eg re-sequencing of scenes in movie.
    #
    # Does not make much sense to select individual frames with audio, best used with ranges.
    # Will coalesce individually selected adjacent frames/ranges before any Fade, ie only audio fade where sensible to do so.
    # TrimAudio==false with non Ordered selection will result in completely out of sync audio.
    c
    TrimAudio=Default(TrimAudio,True)   # default true trims audio, false returns original audio (audiodubbed, as Framesel returns no audio)
    FadeMS=Float(Default(FadeMS,1.0))   # 1 millisecond linear fadeout/fadein at splices
    Ordered=Default(Ordered,True)       # True (default) frames/ranges will be Ordered and selected only once even if specified more than once.
                                        # False, frames/ranges returned in specified order, Cmd processed 1st and then SCmd.
    PruneCmd = (TrimAudio) ? "~Prune_"+RT_LocalTimeString+".txt" : ""
    (!TrimAudio)
        \ ? FrameSel(scmd=SCmd,cmd=Cmd,Ordered=Ordered)
        \ : FrameSel_CmdReWrite(PruneCmd,scmd=SCmd,cmd=Cmd,Ordered=Ordered,Prune=True,range=true)
    (TrimAudio) ? Prune(Cmd=PruneCmd,FadeIn=True,FadeSplice=True,FadeOut=True,Fade=FadeMS) : NOP
    # If TrimAudio==true then delete Prune temp file, Else restore original Audio to the now audio-less clip
    (TrimAudio)
        \ ? RT_FileDelete(PruneCmd)
        \ : (c.HasAudio) ? AudioDub(c) : NOP
    Return Last
}

You can rearrange logic however you will, above was just a quick knock-up.

Requires RT_Stats, FrameSel, Prune, and TWriteAVI v2.0. http://forum.doom9.org/showthread.ph...ight=twriteavi

EDIT:: Oops, and GSCript and Grunt too.

EDIT: This is more like what you asked for, set Show = False to do it for real, when true only shows metric
On my clip it was not deleting anything as all frames were above Ave luma 16.

Avisource("D:\V\StarWars.avi").Trim(0,10000)

GSCript("""
    Function Test(Clip c, int n,Float th,String File,Bool Show) {
        c
        Ave = RT_AverageLuma(n)    
        if(Ave < th) {
            RT_WriteFile(File,"%d",n,Append=True)           # Write unwanted frames (fewer than wanted)
            (Show) ? RT_SubTitle("%d] %f - DELETING",n,Ave) : NOP
        } else {(Show) ? RT_SubTitle("%d] %f",n,Ave) : NOP}
        Return Last    
    }    
""")

OutFile = "Frames.txt"
RT_FileDelete(OutFile)      # Delete existing  
th = 18.0                   # Keep >= 18.0
Show = True                 # CHANGE to FALSE when happy with numbers
SSS = """Test(current_frame,th,OutFile,Show)"""
ARGS="th,OutFile,Show"
ScriptClip(SSS,args=ARGS,after_frame=True)

(!Show)                 ? ForceProcessAVI()         : NOP   # Force Pass 1 (From TWriteAVI v2.0) ie force writing of frames file
(!Show&&Exist(Outfile)) ? RejectRanges(Cmd=Outfile) : NOP   # If Outfile does not exist, then none to Reject. 

Return last    
                
Function RejectRanges(clip c,String "SCmd",String "Cmd",Bool "TrimAudio",Float "FadeMS") {
    # RejectRanges() by StainlessS. Required:- FrameSel, Prune, RT_Stats
    # Wrapper to delete frames/ranges along with audio, can supply frames/ranges in SCmd string And/Or Cmd file.
    #   The wrapper makes for easier usage of Prune() which supports up to 256 input clips, but requires a clip index,
    #   eg '3, 100,200' would specify clip 3, range 100 to 200. The wrapper does away with the necessity for the clip index as we
    #   are only using a single clip here. Prune also does not have a 'reject' arg to delete specified frames rather than select them,
    #   this wrapper also converts a list of frames to delete into a list of frames to select so that we can use Prune and its audio
    #   capability.
    #
    # SCmd: Frames/Ranges specified in String (Frames/Ranges either Chr(10) or ';' separated, infix ',' specifies range, eg 'start,end').
    # Cmd:  Frames/Ranges specified in file (one frame/range per line, comments also allowed, see FrameSel for Further info).
    # TrimAudio:
    #   True(default), deletes audio belonging to deleted frames
    #   False, returns original audio, probably out of sync.
    # FadeMS: (default 1.0 millisec). Linear Audio Fade duration at splices when TrimAudio==true, 0 = dont fade (might result in audio 'clicks/cracks').
    c
    TrimAudio=Default(TrimAudio,True)   # default true trims audio, false returns original audio (audiodubbed, as Framesel returns no audio)
    FadeMS=Float(Default(FadeMS,1.0))   # 1 millisecond linear fadeout/fadein at splices
    PruneCmd = (TrimAudio) ? "~Prune_"+RT_LocalTimeString+".txt" : ""
    (!TrimAudio)
        \ ? FrameSel(scmd=SCmd,cmd=Cmd,reject=true)
        \ : FrameSel_CmdReWrite(PruneCmd,scmd=SCmd,cmd=Cmd,reject=true,Prune=True,range=true)
    (TrimAudio) ? Prune(Cmd=PruneCmd,FadeIn=True,FadeSplice=True,FadeOut=True,Fade=FadeMS) : NOP
    # If TrimAudio==true then delete Prune temp file, Else restore original Audio to the now audio-less clip
    (TrimAudio)
        \ ? RT_FileDelete(PruneCmd)
        \ : (c.HasAudio) ? AudioDub(c) : NOP
    Return Last
}