diff --git a/composer.json b/composer.json
index 8eb45da..3a2048b 100644
--- a/composer.json
+++ b/composer.json
@@ -14,7 +14,7 @@
         }
     ],
     "require": {
-        "php": "^7.2",
+        "php": ">=7.2",
         "symfony/process": "^4.2|^5.0"
     },
     "require-dev": {
diff --git a/src/Media/Media.php b/src/Media/Media.php
index 19bef64..2d66923 100644
--- a/src/Media/Media.php
+++ b/src/Media/Media.php
@@ -26,7 +26,7 @@ class Media extends ExportMedia implements MediaInterface
      * @return Media
      * @throws MediaException
      */
-    public function DRM(string $encryption, callable $options = null)
+    public function DRM(string $encryption, ?callable $options = null)
     {
         $class_name = '\Shaka\Options\DRM\\' . ucwords($encryption);
 
@@ -47,7 +47,7 @@ public function DRM(string $encryption, callable $options = null)
      * @return $this
      * @throws MediaException
      */
-    public function HLS(string $output, callable $options = null)
+    public function HLS(string $output, ?callable $options = null)
     {
         $hls = new HLS();
         $hls = $hls->HLSMasterPlaylistOutput($output);
@@ -62,7 +62,7 @@ public function HLS(string $output, callable $options = null)
      * @return $this
      * @throws MediaException
      */
-    public function DASH(string $output, callable $options = null)
+    public function DASH(string $output, ?callable $options = null)
     {
         $dash = new DASH();
         $dash = $dash->mpdOutput($output);
diff --git a/src/Media/MediaInterface.php b/src/Media/MediaInterface.php
index 8aee538..870220a 100644
--- a/src/Media/MediaInterface.php
+++ b/src/Media/MediaInterface.php
@@ -22,19 +22,19 @@ interface MediaInterface
      * @param callable|null $options
      * @return $this
      */
-    public function DASH(string $output, callable $options = null);
+    public function DASH(string $output, ?callable $options = null);
 
     /**
      * @param string $output
      * @param callable|null $options
      * @return $this
      */
-    public function HLS(string $output, callable $options = null);
+    public function HLS(string $output, ?callable $options = null);
 
     /**
      * @param string $encryption
      * @param callable|null $options
      * @return Media
      */
-    public function DRM(string $encryption, callable $options = null);
+    public function DRM(string $encryption, ?callable $options = null);
 }
\ No newline at end of file
diff --git a/src/helpers.php b/src/helpers.php
index d25cfcd..c72a3f9 100644
--- a/src/helpers.php
+++ b/src/helpers.php
@@ -17,7 +17,7 @@
      * @return mixed
      * @throws \Shaka\Exception\ProcessException
      */
-    function shaka(string $binary = null)
+    function shaka(?string $binary = null)
     {
         return \Shaka\Shaka::initialize($binary);
     }