"...because the geometry of the abyss demands it"

README.org

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+
+* time, space, stacking, slicing, scanning, etc 
+
+"Slitscan imaging techniques are used to create static images of time-based phenomena. In traditional film photography, slit scan images are created by exposing film as it slides past a slit-shaped aperture. In the digital realm, thin slices are extracted from a sequence of video frames, and concatenated into a new image."
+
+[[http://www.flong.com/texts/lists/slit_scan/][An Informal Catalogue of Slit-Scan Video Artworks and Research]] Compiled by Golan Levin.
+
+#+ATTR_HTML: :style margin-left: auto; margin-right: auto;
+#+name: unfolding
+#+caption: Egbert Mittelstaedt. Unfolding (2002)
+[[http://www.flong.com/storage/images/texts/slit_scan/34_egbert_mittelstaedt_665px.jpg]]
+
+This particular slitscan provides some slightly configurable scaffolding around ffmpeg (based on a blogpost from [[http://oioiiooixiii.blogspot.com/2017/11/ffmpeg-temporal-slice-stacking-effect.html][oioiiooixiii]]) and is intended for non-realtime rendering at various resolutions. it's neither first, nor last. it's not especially interesting, educational or efficient. just another cloudform in the endless space of possible implementation... 
+
+* installation, configuration, operation, etc
+
+install (mac)...
+#+BEGIN_SRC shell
+brew install ffmpeg drracket
+git clone https://github.com/zzkt/slitscan.git
+#+END_SRC
+
+install (debian/ubuntu)...
+#+BEGIN_SRC shell
+sudo apt install ffmpeg racket
+git clone https://github.com/zzkt/slitscan.git
+#+END_SRC
+
+simple transform...
+#+BEGIN_SRC shell
+racket slitscan.rkt -v -i <input.mp4> 
+#+END_SRC
+
+transform at 1080p and delete working files, with minimal command line noise...
+#+BEGIN_SRC shell
+racket slitscan.rkt --width 1920 --height 1080 --loglevel quiet --cleanup -i <input.mp4> 
+#+END_SRC
+
+options...
+#+BEGIN_SRC shell
+slitscan [ <option> ... ]
+ where <option> is one of
+  -v, --verbose : various verbose messages
+  -l <level>, --loglevel <level> : loglevel for ffmpeg e.g. quiet, error, warning, info, debug
+  -c, --cleanup : Clean up temporary/working files
+  --horizontal : output a horizontal video only (default: both)
+  --vertical : output a vertical video only (default: both)
+  --width <pixels> : width of output output video
+  --height <pixels> : height of output output video
+  -i <video>, --input <video> : input file
+  -f <folder>, --folder <folder> : input folder
+  --help, -h : Show this help
+#+END_SRC
+
+
+* further reading
+
+  - The Fourth Dimension and How to Get There by Rudy Rucker
+  - Muybridge's Complete Human and Animal Locomotion, Vol. I
+  - Baroness Elsa, by Irene Gammel

slitscan.rkt

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+#! /usr/bin/env racket
+#lang racket
+
+;;; Temporal slice-stacking with FFmpeg (aka slitscan, etc+)
+;;;
+;;; Copyright (C) 2019 FoAM
+;;;
+;;;  This program is free software: you can redistribute it and/or modify
+;;;  it under the terms of the GNU General Public License as published by
+;;;  the Free Software Foundation, either version 3 of the License, or
+;;;  (at your option) any later version.
+;;;
+;;;  This program is distributed in the hope that it will be useful,
+;;;  but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;;  GNU General Public License for more details.
+;;;
+;;;  You should have received a copy of the GNU General Public License
+;;;  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+;;;
+;;; 
+;;; Authors 
+;;;
+;;;  nik gaffney <nik@fo.am>
+;;;
+;;; Requirements
+;;;
+;;;  Racket, ffmpeg and zsh or bash (probably)
+;;;
+;;; Commentary
+;;;
+;;;  Mostly scaffolding around ffmpeg, based on a shell script from oioiiooixiii
+;;;   http://oioiiooixiii.blogspot.com/2017/11/ffmpeg-temporal-slice-stacking-effect.html
+;;; 
+;;;  Further details, instructions and digression can be found at
+;;;   https://github.com/zzkt/slitscan/
+;;;
+;;; Revision history
+;;; 
+;;;  - 2017-10-01 - shell script from oioiiooixiii 
+;;;  - 2019-08-08 - cmprzs, convert, reconstruct
+;;;  - 2019-08-10 - racket translation, info 
+
+
+;; cli options
+(define verbose? (make-parameter #f))
+(define cleanup? (make-parameter #f))
+(define filename (make-parameter "untitled"))
+(define input-folder (make-parameter ""))
+(define loglevel (make-parameter "")) ;; leave unset by default
+
+;; output options horiz/vert/both
+(define hout-only? (make-parameter #f))
+(define vout-only? (make-parameter #f))
+
+(define output-width  (make-parameter 640))
+(define output-height (make-parameter 360))
+
+;; parse command line
+(define getopt  
+  (command-line
+   #:program "slitscan"
+   #:once-each
+   (("-v" "--verbose")  "various verbose messages" (verbose? #t))
+   (("-l" "--loglevel") level "loglevel for ffmpeg e.g. quiet, error, warning, info, debug" (loglevel level))
+   (("-c" "--cleanup")  "Clean up temporary/working files" (cleanup? #t))
+   (("--horizontal")    "output a horizontal video only (default: both)" (hout-only? #t))
+   (("--vertical")      "output a vertical video only (default: both)" (vout-only? #t))
+   (("--width")         pixels "width of transform video" (output-width pixels))
+   (("--height")        pixels "height of tansform video"  (output-height pixels))   
+   (("-i" "--input")    video "input file" (filename video))
+   (("-f" "--folder")   folder "input folder"  (input-folder folder))
+   #:args () ; rest of the args? 
+   (printf "slitscanning: ~a\n" (filename))))
+
+;; emulation of $(...) shell syntax 
+(define-syntax zout 
+  (syntax-rules ()
+    ((_ cmd) (string-trim (with-output-to-string (lambda () (system cmd)))))))
+
+;; echoing verbosity
+(define-syntax vecho
+  (syntax-rules ()
+    ((_ str ...) (when (verbose?) (printf str ...)))))
+
+(cond ((and (verbose?) (string=? "" (loglevel))) (loglevel "info"))
+      ((and (not (verbose?)) (string=? "" (loglevel))) (loglevel "error")))
+
+;; variables/various
+(define folder (if (not (string=? "" (input-folder)))
+                   (input-folder) 
+                   (zout "mktemp -d")))
+
+(vecho "using folder: ~a\n" folder)
+
+;(define fffeature "ffprobe -v quiet -select_streams v -of default=noprint_wrappers=1:nokey=1 -show_entries stream=")
+
+(define fffeature "ffprobe -v error -of default=noprint_wrappers=1:nokey=1 -show_entries format=")
+
+;; assume most/all codecs/formats/streams have a duration
+(define duration (let ((f (string->number
+                            (zout (format
+                                   "~aduration \"~a\""
+                                   fffeature (filename))))))
+                    (if f f 0)))
+
+(vecho "duration: ~a seconds\n" duration)
+
+;; determine fps from input file or default to 24
+(define fps (let ((f (string->number
+                      (zout (format
+                             "~ar_frame_rate \"~a\""
+                             fffeature (filename))))))
+              (if f f 24)))
+
+(vecho "fps: ~a\n" fps)
+
+;; number of frames. estimate for codecs/formats/streams without nb_frames 
+(define frames (let ((f (string->number
+                           (zout (format
+                                  "~anb_frames \"~a\""
+                                  fffeature (filename))))))
+                   (if f f (ceiling (* duration fps)))))
+
+(vecho "frames: ~a\n" frames)
+
+;; output dimensions. change if/as required via opts...
+(define w (output-width)) 
+(define h (output-height))
+
+(vecho "transform dimensions: ~ax~a\n" w h)
+
+;; FFmpeg Filterchains
+(define stemStart "select=gte(n\\,")
+(define stemEnd "),format=yuv444p,split[horz][vert]")
+(define horz (format "[horz]crop=in_w:1:0:n,tile=1x~a[horz]" h))
+(define vert (format "[vert]crop=1:in_h:n:0,tile=~aX1[vert]" w))
+(define merge "[0:v]null[horz];[1:v]null[vert]")
+(define scale (format "scale=~a:~a" w h))
+
+;; check resume?
+
+;; rezise video
+(define resized-video (string-append folder "/resized.mkv"))
+
+(define (resize)
+  (define ffmpeg-r1
+    (format "ffmpeg -loglevel ~a -i \"~a\" -vf ~a -crf 10 \"~a\" 2>&1 | grep 'frame=' | tr \\n \\r; echo"
+             (loglevel) (filename) scale resized-video)) 
+  (vecho "resizing video: ~a\n" resized-video)
+  (system ffmpeg-r1))
+
+
+;; slice/crop/loop
+(define (slice)
+  (for ((i (range frames))) 
+    (vecho "Frame: ~a of ~a\r" i frames)
+    (define ffmpeg-s1 
+      (format     
+       "ffmpeg -loglevel ~a -i \"~a\" \
+        -filter_complex \"~a~a~a;~a;~a\"  \
+        -map '[horz]' \
+          -vframes 1 ~a/horz_frame~a.png \
+        -map '[vert]' \
+          -vframes 1 ~a/vert_frame~a.png"
+       (loglevel) resized-video
+       stemStart i stemEnd horz vert
+       folder i
+       folder i))
+    (system ffmpeg-s1))
+  (vecho "\n"))
+
+
+;; Join images (optional sharpening, upscale, etc. via 'merge' variable)
+(define (assemble)
+  (vecho "Creating output videos\n")
+
+  (define ffmpeg-a0  ;; horizontal & vertical videos (from .sh) 
+    (format   
+     "ffmpeg -loglevel ~a \
+      -r ~a -i ~a/horz_frame%d.png \
+      -r ~a -i ~a/vert_frame%d.png \
+      -filter_complex \"~a\" \
+      -map '[horz]' \
+        -r ~a \
+        -crf 10 \
+        \"~a_horizontal-smear.mkv\" \
+      -map '[vert]' \
+        -r ~a \
+        -crf 10 \
+        \"~a_vertical-smear.mkv\""
+     (loglevel) 
+     fps folder
+     fps folder 
+     merge 
+     fps (filename)
+     fps (filename)))
+
+  (define ffmpeg-a1 ;; horizontal frame stack 
+    (format   
+     "ffmpeg -loglevel ~a -r ~a -i ~a/horz_frame%d.png \"~a_horizontal-smear.mkv\""
+      (loglevel) fps folder (filename)))
+
+  (define ffmpeg-a2 ;; vertical frame stack 
+    (format   
+     "ffmpeg -loglevel ~a -r ~a -i ~a/vert_frame%d.png \"~a_vertical-smear.mkv\""
+      (loglevel) fps folder (filename)))
+  
+  ;; assemble
+  (cond  ((hout-only?) (system ffmpeg-a1))  
+         ((vout-only?) (system ffmpeg-a2))
+         (else (system ffmpeg-a1)
+               (system ffmpeg-a2))))
+
+;; spatial extents (frames -> image) summary
+(define (framecat start offset)
+  (define montage-h1
+    (format "montage ~a/horz_frame~a.png ~a/horz_frame~a.png ~a/horz_frame~a.png ~a/horz_frame~a.png ~a/horz_frame~a.png -tile x1 -mode concatenate ~a-slitscan-s~a.o~a.jpg"
+            folder start
+            folder (+ start offset)
+            folder (+ start (* offset 2))
+            folder (+ start (* offset 3))
+            folder (+ start (* offset 4))
+            (filename) start offset))
+  (system montage-h1))
+
+(define (image) (framecat 1 (/ frames 5)))
+               
+;; delete working files (or not) 
+(define (cleanup)
+  (if (cleanup?)
+      (begin (system (format "rm -rf ~a" folder))
+             (printf "Removed temp files at ~a\n" folder))
+      (vecho "leaving working files at ~a\n" folder)))
+
+;; output in 3 (or 4 (or 5)) steps
+
+(when (resize)   (printf "resized\n"))
+(when (slice)    (printf "slicwd\n"))
+(when (assemble) (printf "assembled\n"))
+(when (cleanup)  (printf "done\n"))
+
+;;; FIN