Set default value for max video height

src/Model/Item.php

@@ -3644,7 +3644,7 @@ class Item
 
 			if ($PostMedia->mimetype->type == 'video') {
 				if (($PostMedia->height ?? 0) > ($PostMedia->width ?? 0)) {
-					$height = min(DI::config()->get('system', 'max_video_height'), $PostMedia->height);
+					$height = min(DI::config()->get('system', 'max_video_height') ?: '100%', $PostMedia->height);
 					$width  = 'auto';
 				} else {
 					$height = 'auto';

static/defaults.config.php

@@ -407,6 +407,10 @@ return [
 		// Maximum recursion depth when fetching posts until the job is delegated to a worker task or finished.
 		'max_recursion_depth' => 50,
 
+		// max_video_height (Integer)
+		// Maximum height of videos in portrait mode.
+		'max_video_height' => 640,
+
 		// memcache_host (String)
 		// Host name of the memcache daemon.
 		'memcache_host' => '127.0.0.1',