diff --git a/src/FFMpeg/Format/Video/X264.php b/src/FFMpeg/Format/Video/X264.php
index c1fd453..7670910 100644
--- a/src/FFMpeg/Format/Video/X264.php
+++ b/src/FFMpeg/Format/Video/X264.php
@@ -22,7 +22,7 @@ class X264 extends DefaultVideo
     /** @var int */
     private $passes = 2;
 
-    public function __construct($audioCodec = 'libfaac', $videoCodec = 'libx264')
+    public function __construct($audioCodec = 'aac', $videoCodec = 'libx264')
     {
         $this
             ->setAudioCodec($audioCodec)
diff --git a/src/FFMpeg/Media/AbstractVideo.php b/src/FFMpeg/Media/AbstractVideo.php
index 339e4da..8384b98 100644
--- a/src/FFMpeg/Media/AbstractVideo.php
+++ b/src/FFMpeg/Media/AbstractVideo.php
@@ -86,6 +86,10 @@ abstract class AbstractVideo extends Audio
                     // FFMpeg\Format\ProgressListener\AbstractProgressListener class
                     foreach ($filters as $filter) {
                         if ($filter instanceof ClipFilter) {
+                            if ($filter->getDuration() === NULL) {
+                                continue;
+                            }
+                            
                             $duration = $filter->getDuration()->toSeconds();
                             break;
                         }