fix the generation of video preview attachments

js/modules/types/visual_attachment.js

@@ -103,6 +103,8 @@ exports.makeVideoScreenshot = ({
     });
 
     video.src = objectUrl;
+    // for some reason, this is to be started, otherwise the generated thumbnail will be empty
+    video.play();
   });
 
 exports.makeVideoThumbnail = async ({

js/views/file_input_view.js

@@ -1,6 +1,4 @@
-/* global textsecure: false */
 /* global Whisper: false */
-/* global loadImage: false */
 /* global Backbone: false */
 /* global _: false */
 /* global Signal: false */
@@ -26,7 +24,6 @@
       });
     },
 
-
     render() {
       this.attachmentListView.update(this.getPropsForAttachmentList());
       this.trigger('staged-attachments-changed');
@@ -184,6 +181,7 @@
 
       const renderVideoPreview = async () => {
         const objectUrl = URL.createObjectURL(file);
+
         try {
           const type = 'image/png';
           const thumbnail = await VisualAttachment.makeVideoScreenshot({