Probably fixed things by not really doing anything in particular?

src/FFMPEG.php

@@ -3,6 +3,7 @@ namespace Uiharu;
 
 use stdClass;
 use Imagick;
+use RuntimeException;
 use Index\IO\Stream;
 use Index\IO\ProcessStream;
 
@@ -23,23 +24,35 @@ final class FFMPEG {
     }
 
     public static function probe(string $url): ?object {
-        return json_decode(
-            shell_exec(
-                sprintf(
+        $command = sprintf(
             'ffprobe -show_streams -show_format -print_format json -v quiet -i %s',
             escapeshellarg($url)
-                )
-            )
         );
+
+        $ffprobe = proc_open($command, [1 => ['pipe', 'w'], 2 => ['pipe', 'w']], $pipes);
+        if(!is_resource($ffprobe))
+            throw new RuntimeException('Could not open ffprobe.');
+
+        try {
+            $stderr = trim(stream_get_contents($pipes[2]));
+            if(!empty($stderr))
+                throw new RuntimeException('ffprobe: ' . $stderr);
+
+            $stdout = trim(stream_get_contents($pipes[1]));
+            if(empty($stdout))
+                throw new RuntimeException('ffprobe did not report any errors but exited without any output');
+        } finally {
+            proc_close($ffprobe);
+        }
+
+        return json_decode($stdout);
     }
 
     public static function cleanProbe(string $url): ?object {
         return self::cleanProbeResult(self::probe($url));
     }
 
-    public static function cleanProbeResult(?object $in): ?object {
-        if($in === null)
-            return null;
+    public static function cleanProbeResult(?object $in): object {
         $out = new stdClass;
 
         if(!empty($in->format)) {

src/Lookup/WebLookupMediaResult.php

@@ -4,6 +4,7 @@ namespace Uiharu\Lookup;
 use Uiharu\AudioTags;
 use Uiharu\Url;
 use Index\MediaType;
+use Index\Colour\Colour;
 
 class WebLookupMediaResult extends WebLookupResult implements \Uiharu\IHasMediaInfo {
     private object $mediaInfo;
@@ -26,7 +27,7 @@ class WebLookupMediaResult extends WebLookupResult implements \Uiharu\IHasMediaI
     public function hasColour(): bool {
         return false;
     }
-    public function getColour(): int {
+    public function getColour(): Colour {
         throw new RuntimeException('Unsupported');
     }