YouTube FLV - http://www.abdulqabiz.com/blog/archives/2006/11/26/youtube-actionscript-20-api/

youtubeflv.php

<?php
// Youtube FLV Fetcher
// Responds to both HTTP GET and POST requests
// Author: Abdul Qabiz (abdul dot qabiz at gmail dot com)
//
// Description:Gets the path of FLV from YouTube URL
// Is it a POST or a GET?
if (isset($_GET['url']))
{
  $url = $_GET['url'];
  $v = $url;
  $v = preg_split ("/\?v=/", $v);
  //youtube video-id
  $v = $v[1];
  //hardcoding URL here, couldn't figure how to make CURL follow 303 redirection
  //seems something wrong with libCurl or my knowledge...
  $url = "http://www.youtube.com/watch?v=" . $v;
  //Start the Curl session
  $session = curl_init();
  curl_setopt ($session, CURLOPT_URL, $url);
  //you might want to turn it to false, in case you want
  //to content to client (flash etc).
  curl_setopt($session, CURLOPT_HEADER, true);
  //not working for me :(
  curl_setopt($session, CURLOPT_FOLLOWLOCATION, true);
  //curl_setopt($ch, CURLOPT_TIMEOUT, 10);
  curl_setopt($session, CURLOPT_RETURNTRANSFER, true);
  // Make the call
  $response = curl_exec($session);
  if (preg_match_all("/&t=[^&]*/", $response, $matches))
  {
    $t = $matches[0][0];
    $t = preg_split("/=/", $t);
    //youtube t param
    $t = $t[1];
    //construct the flv-url
    $youtubeVideoPath = "http://www.youtube.com/get_video.php?video_id=" . $v . "&t=". $t . "&.flv";
    //redirect to flv -  you can replace this code with echo/print
    //to return the path to client (browser/flash)
    header ("Location: $youtubeVideoPath");
  } else {
    echo "null";
  }
  curl_close($session);
} else {
  echo "No YouTube URL to process";
}
?>