Using PHP with resumable downloads and encrypted files

Question

I have a project that encrypts uploaded files and saves them. Those files are hidden from the users while still able to see them (by using php).

The code below works perfectly with images and all other files with sizes 0-2MB. The problem is larger files (> 2MB) that is used to send to a browser in requested range of bytes. Like videos with HTML5 video.

There is lots of similar questions available but I still haven't got that to work with encrypted large files.

How to get this code to work properly with large files and decryption so that the users browser will understand it and show the contents? Is there some headers what I'm missing or what I have done wrong?

Here's the current code:

<?php
function printFileChunksRange($file, $key){

    //$_SERVER["HTTP_RANGE"]="bytes=0-"; // For testing

    $fp = fopen($file['url'], 'rb');
    $size   = $file['size'];       // File size
    $length = $size;               // Content length
    $start  = 0;                   // Start byte
    $end    = $size - 1;           // End byte
    $chunkSize = 1024*100;         // Chunk size used to crypt files
    $readChunkSize = $chunkSize+8; // Chunk size + IV size

    // parse the range of bytes
    if(!empty($_SERVER['HTTP_RANGE'])){
        if(preg_match('/bytes=\h*(\d+)-(\d*)[\D.*]?/i', $_SERVER['HTTP_RANGE'], $matches)){
            $start = intval($matches[1]); // Start byte
            if(!empty($matches[2])){
                $end = intval($matches[2]); // End byte
            }
        }
    }

    if($start > $end) $end = $file['size']-1;
    $length = $end-$start;

    if(isset($_SERVER['HTTP_RANGE'])) header('HTTP/1.1 206 Partial Content'); // Send the header code 206 if range is requested...
    else header('HTTP/1.1 200 OK'); // ...otherwise send 200

    // Set the rest of headers
    header("Content-type: {$file['type']}");                      // File type
    header('Cache-Control: public, must-revalidate, max-age=0');  // ...
    header('Accept-Ranges: bytes');                               // Say that ranges is accepted
    if(isset($_SERVER['HTTP_RANGE'])) header("Content-Range: bytes {$start}-{$end}/{$file['size']}"); // Tell that what bytes we'll send
    header("Content-Length: ".(($end-$begin)+1)); //$length // Content length
    //Header("Connection: close");

    // Count the chunk sizes.. etc. ...for the start of requested range
    $chunk_start = intval(floor($start/$chunkSize));
    $chunk_start_bytes = intval($chunk_start*$readChunkSize);
    $chunk_start_remainder = intval($start % $chunkSize);

    // Count the chunk sizes.. etc. ...for the end of requested range
    $chunk_end = intval(floor($end/$chunkSize));
    $chunk_end_bytes = intval($chunk_end*$readChunkSize);
    $chunk_end_remainder = intval(($end+1) % $chunkSize);

    fseek($fp, $chunk_start_bytes); // Seek the right byte to start reading
    set_time_limit(0);              // Set time limit to 0, for large files
    $current = 0;                   // Current output length

    while(!feof($fp) and $current <= $length and connection_status() == 0) {
        $data = fread($fp, $readChunkSize); // Read encrypted chunk...
        $data = $this->decrypt($data, $key); // ...and decrypt it

        if($start+$end < $chunkSize)                 $data = substr($data, $chunk_start_remainder, $chunk_end_remainder-$chunk_start_remainder);
        elseif($current + strlen($data) > $length+1) $data = substr($data, $chunk_start_remainder, $chunk_end_remainder);
        else                                         $data = substr($data, $chunk_start_remainder);

        $chunk_start_remainder = 0; // Set remainder to 0, because we have already used it and we don't need it anymore;
        $current += strlen($data);  // Add $data length to $current output length

        echo $data; // Print the decrypted chunk
        flush();    // Free up memory to save server's resources
    }
    fclose($fp); // Close the file handle
}
?>

And the usage for the code above:

<?php
$file = array(
    'type' => 'video/mp4',
    'ext' => 'mp4',
    'name' => '6XjQALY3YG',
    'size' => '15765276',
    'original_name' => '20130908.mp4',
    'key' => 'feab20c63f84788ad7cb90b547946bccb5da8a9d0b4ffb6473c70a732ae8df99',
    'url' => 'upload/2013/12/17/6XjQALY3YG',
    //'url' => 'bigfile.mp4',
);

printFileChunksRange($file, $file['key']);
?>

http://mobiforge.com/design-development/content-delivery-mobile-devices
Resumable downloads when using PHP to send the file?
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html