Ensure that multi-video lightbox scrolling changes video

ts/components/Lightbox.tsx

@@ -289,6 +289,7 @@ export class Lightbox extends React.Component<Props> {
           onClick={this.playVideoBound}
           controls={true}
           style={styles.object}
+          key={objectURL}
         >
           <source src={objectURL} />
         </video>

ts/components/LightboxGallery.md

@@ -33,29 +33,35 @@ const mediaItems = [
     attachment: { contentType: 'video/mp4' },
   },
   {
-    objectURL: 'https://placekitten.com/980/800',
-    contentType: 'image/jpeg',
+    objectURL: util.mp4ObjectUrlV2,
+    contentType: 'video/mp4',
     message: { id: 5 },
-    attachment: { contentType: 'image/jpeg' },
+    attachment: { contentType: 'video/mp4' },
   },
   {
-    objectURL: 'https://placekitten.com/656/540',
+    objectURL: 'https://placekitten.com/980/800',
     contentType: 'image/jpeg',
     message: { id: 6 },
     attachment: { contentType: 'image/jpeg' },
   },
   {
-    objectURL: 'https://placekitten.com/762/400',
+    objectURL: 'https://placekitten.com/656/540',
     contentType: 'image/jpeg',
     message: { id: 7 },
     attachment: { contentType: 'image/jpeg' },
   },
   {
-    objectURL: 'https://placekitten.com/920/620',
+    objectURL: 'https://placekitten.com/762/400',
     contentType: 'image/jpeg',
     message: { id: 8 },
     attachment: { contentType: 'image/jpeg' },
   },
+  {
+    objectURL: 'https://placekitten.com/920/620',
+    contentType: 'image/jpeg',
+    message: { id: 9 },
+    attachment: { contentType: 'image/jpeg' },
+  },
 ];
 
 <div style={{ position: 'relative', width: '100%', height: 500 }}>

ts/styleguide/StyleGuideUtil.ts

@@ -29,6 +29,9 @@ const txtObjectUrl = makeObjectUrl(txt, 'text/plain');
 import mp4 from '../../fixtures/pixabay-Soap-Bubble-7141.mp4';
 const mp4ObjectUrl = makeObjectUrl(mp4, 'video/mp4');
 // @ts-ignore
+import mp4v2 from '../../fixtures/ghost-kitty.mp4';
+const mp4ObjectUrlV2 = makeObjectUrl(mp4v2, 'video/mp4');
+// @ts-ignore
 import png from '../../fixtures/freepngs-2cd43b_bed7d1327e88454487397574d87b64dc_mv2.png';
 // 800×1200
 const pngObjectUrl = makeObjectUrl(png, 'image/png');
@@ -69,6 +72,8 @@ export {
   gifObjectUrl,
   mp4,
   mp4ObjectUrl,
+  mp4v2,
+  mp4ObjectUrlV2,
   png,
   pngObjectUrl,
   txt,