Update PreviewManager.php

add a check in config.php for a configured movieBinary path.
so now it first checks in config.php if  preview_ffmpeg_path is configured.

Signed-off-by: William <william.hak57@gmail.com>

lib/private/PreviewManager.php

@@ -417,11 +417,16 @@ class PreviewManager implements IPreview {
 
 		// Video requires avconv or ffmpeg
 		if (in_array(Preview\Movie::class, $this->getEnabledDefaultProvider())) {
-			$movieBinary = $this->binaryFinder->findBinaryPath('avconv');
-			if (!is_string($movieBinary)) {
-				$movieBinary = $this->binaryFinder->findBinaryPath('ffmpeg');
+
+			$movieBinary = $this->config->getSystemValue('preview_ffmpeg_path', null);
+			if(!is_string($movieBinary)){
+				$movieBinary = $this->binaryFinder->findBinaryPath('avconv');
+				if (!is_string($movieBinary)) {
+					$movieBinary = $this->binaryFinder->findBinaryPath('ffmpeg');
+				}
 			}
 
+
 			if (is_string($movieBinary)) {
 				$this->registerCoreProvider(Preview\Movie::class, '/video\/.*/', ["movieBinary" => $movieBinary]);
 			}