accept-ranges.php

<?php
$file = 'path-to-file';
$size = filesize($file);
$start = 0;
$end = $size - 1;
if (preg_match('/bytes=(\d+)-(\d*)/i', $_SERVER['HTTP_RANGE'] ?? '', $matches)) {
	$start = $matches[1];
	if (!empty($matches[2])) {
		$end = $matches[2];
	}
	header('HTTP/1.1 206 Partial Content');
	header('Content-Range: bytes ' . $start . '-' . $end . '/' . $size);
}
header('Accept-Ranges: bytes');
header('Content-Type: ' . mime_content_type($file));
$required = $end + 1 - $start;
$sent = 0;
$fh = fopen($file, 'r');
fseek($fh, $start);
do {
	$buffer = fread($fh, 4096);
	$sent += strlen($buffer);
	echo $buffer;
} while ($sent < $required);
fclose($fh);