a hastily-written puggsy prototype video data decoder

i.php

<?php

	/*
		JonTT's Puggsy prototype video decoder
		Hastily written at one in the morning

		Get the video
		$ youtube-dl https://www.youtube.com/watch?v=2ZdXmhwcbhQ

		Give it a more reasonable name
		$ mv WE\ REACHED\ 3\,000\ SUBS\,\ SO\ HERE\'S\ A\ CHALLENGE\!\ Do\ you\ accept-2ZdXmhwcbhQ.mp4 burp.mp4

		Extract frames into individual images
		$ ffmpeg -i burp.mp4 -f image2 images%06d.png

		Delete images before images000807 and after images000902 (not part of data)
		Then run this thing. It will dump out.bin into your directory

	*/

	// Tracking pages of data
	$page	= 0;			// Current page
	$pagel	= false;		// Last image was separator
	$pages	= [];			// Page data

	for ($ii = 807; $ii <= 902; $ii++) {
		$file	= sprintf("/tmp/burp/images%06d.png", $ii);
		print $file ."\n";

		// Gets a string of 0 and 1 (or null if separator)
		$d		= decodeimage($file);

		if ($d === null && $pagel !== true) {
			// If first not-a-page image, move to the next page
			$page++;
			$pagel	= true;
			print "Separator image\n";
			continue;
		} elseif ($d === null) {
			// If still not a page, keep going
			print "Separator image\n";
			continue;
		}
		$pagel	= false;

		// Page, probably. Go ahead and copy it
		if (!isset($pages[$page])) {
			// New page, copy it in
			$pages[$page]	= $d;
			print "Decoded page $page\n";
		} else {
			if ($pages[$page] === $d) {
				// Different image, same data, looks good
				print "Verified page $page\n";
			} else {
				// This page was already decoded, but for some reason
				// this particular attempt didn't match
				// No attempt at resolution is made
				print "Page $page MISMATCH!\n";

			}
		}
	}

	// Concat every page
	$total	= "";
	foreach ($pages as $page) {
		$total	.= $page;
	}
	$len		= strlen($total);
	print "Len: ". $len ." (". ($len / 8) .")\n";

	// Convert every 8 characters into one byte
	$out		= "";
	for ($cp = 0; $cp < $len; $cp += 8) {
		$bin	= substr($total, $cp, 8);
		$out	.= chr(bindec($bin));
	}

	// Dump to file
	file_put_contents("out.bin", $out);



	// The magic happens here
	function decodeimage($file) {
		$img	= imagecreatefrompng($file);

		// The top left pixel of all data pages is red
		if (pixel(ica($img, 0, 0)) !== null) {
			return null;
		}

		// Padding area
		$px		= 6;
		$py		= 4;

		// Approximate size of pixels
		// I assume these were an even 4 before the padding was added
		$sx		= 3.9632;
		$sy		= 3.962;

		// Count of pixels
		$cx		= 320;
		$cy		= 180;

		// Old cruft
		$cf		= 0;
		$c1		= 0;
		$c0		= 0;

		$str	= "";

		for ($y = 0; $y < $cy; $y++) {
			for ($x = 0; $x < $cx; $x++) {
				// Based on internal x/y, get image x/y
				$ax		= ceil($px + ($x * $sx));
				$ay		= ceil($py + ($y * $sy));

				// Get actual color values for our pixel
				$ics	= ica($img, $ax, $ay);
				// Get bit
				$z		= pixel($ics);
				if ($z === -1) {
					// Not red, but not solidly black/white either
					print "$file: Unknown pixel @ $ax, $ay: $ics[r] $ics[g] $ics[b]\n";
				}
				if ($z === true) {
				 	$str	.= "1";
				}
				if ($z === false) {
					$str	.= "0";
				}
			}
		}

		return $str;
	}


	function ica($i, $x, $y) {
		$rgb = imagecolorat($i, $x, $y);
		$r = ($rgb >> 16) & 0xFF;
		$g = ($rgb >> 8) & 0xFF;
		$b = $rgb & 0xFF;
		return ['r' => $r, 'g' => $g, 'b' => $b];
	}

	function pixel($a) {
		// Technically these can be whatever, but these values worked for me
		$maxBlack	= 0x60;
		$minWhite	= 0xA0;

		// Red pixel
		if (
			$a['r'] > 0xB0 &&
			$a['g'] < 0x80 &&
			$a['b'] < 0x80
		) {
			return null;
		}


		// White pixel ("on")
		if (
			$a['r'] > $minWhite &&
			$a['g'] > $minWhite &&
			$a['b'] > $minWhite
		) {
			return true;
		}


		// Black pixel
		if (
			$a['r'] < $maxBlack &&
			$a['g'] < $maxBlack &&
			$a['b'] < $maxBlack
		) {
			return false;
		}

		return -1;

	}