From a16e03df3f2d5cd982bee76b1f14101464aa196a Mon Sep 17 00:00:00 2001
From: Paul Nicholls <paul.nicholls@canterbury.ac.nz>
Date: Thu, 12 Feb 2015 09:34:33 +1300
Subject: [PATCH] MDL-49059 medialib: Support links to Youtube videos within
 playlists

As well as embedding playlists, you can embed specific videos from them -
resulting in the playlist UI displaying, but starting with the specified
video rather than the first in the playlist.  Previously, just the
specified video would embed - without the playlist UI.
---
 lib/medialib.php | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/medialib.php b/lib/medialib.php
index f4583c4eb95..9725e3550d7 100644
--- a/lib/medialib.php
+++ b/lib/medialib.php
@@ -542,6 +542,13 @@ class core_media_player_youtube extends core_media_player_external {
             $params .= "start=$start&";
         }
 
+        $listid = $url->param('list');
+        // Check for non-empty but valid playlist ID.
+        if (!empty($listid) && !preg_match('/[^a-zA-Z0-9\-_]/', $listid)) {
+            // This video is part of a playlist, and we want to embed it as such.
+            $params .= "list=$listid&";
+        }
+
         return <<<OET
 <span class="mediaplugin mediaplugin_youtube">
 <iframe title="$info" width="$width" height="$height"