fix #14

cli.js

@@ -91,11 +91,10 @@ const cli = meow(`
 
   const { verbose, transitionName, transitionDuration, width, height, fps, audioFilePath, fontPath, fast, out: outPath } = cli.flags;
 
-  if (transitionName || transitionDuration) {
-    params.defaults.transition = {
-      name: transitionName,
-      duration: transitionDuration,
-    };
+  if (transitionName || transitionDuration != null) {
+    params.defaults.transition = {};
+    if (transitionName) params.defaults.transition.name = transitionName;
+    if (transitionDuration) params.defaults.transition.duration = transitionDuration;
   }
 
   if (fontPath) {

transitions.js

@@ -38,8 +38,8 @@ function calcTransition(defaults, transition) {
 
   assert(!transitionOrDefault.duration || transitionOrDefault.name, 'Please specify transition name or set duration to 0');
 
-  if (transitionOrDefault.name === 'random') {
-    transitionOrDefault = { easing: transitionOrDefault.easing, name: getRandomTransition(), duration: 0.5 };
+  if (transitionOrDefault.name === 'random' && transitionOrDefault.duration) {
+    transitionOrDefault = { easing: transitionOrDefault.easing, name: getRandomTransition(), duration: transitionOrDefault.duration };
   }
 
   const getTransitionByAlias = () => {