diff --git a/src/servers/api/file-browser/thumbnails.ts b/src/servers/api/file-browser/thumbnails.ts
index 5e1596f8..82de48be 100644
--- a/src/servers/api/file-browser/thumbnails.ts
+++ b/src/servers/api/file-browser/thumbnails.ts
@@ -44,7 +44,33 @@ import sharp from 'sharp';
  * file icons was the most visible gap this had.
  */
 const IMAGE_EXT = new Set(['jpg', 'jpeg', 'png', 'gif', 'webp', 'bmp', 'avif', 'tif', 'tiff', 'svg', 'heic', 'heif']);
-const VIDEO_EXT = new Set(['mp4', 'mov', 'm4v', 'webm', 'mkv', 'avi', 'wmv', 'flv', 'mpg', 'mpeg', 'ts', '3gp']);
+/*
+  `ts` is NOT here, and that is the one entry worth explaining.
+
+  It is a real video extension — MPEG transport stream — and it was in this list until a deploy to fofos
+  reported `test-setup.ts` as a video. On any machine Officer runs on, `.ts` is TypeScript approximately
+  always, so including it meant every source file in every repository drew a play badge and spawned an
+  ffmpeg that could only fail.
+
+  The two ways of being wrong are not the same size. Excluded, a genuine transport stream shows a file
+  icon; included, browsing a source tree runs a decoder per file. Nobody stores broadcast captures in a
+  folder they browse from here.
+*/
+const VIDEO_EXT = new Set([
+  'mp4',
+  'mov',
+  'm4v',
+  'webm',
+  'mkv',
+  'avi',
+  'wmv',
+  'flv',
+  'mpg',
+  'mpeg',
+  '3gp',
+  'm2ts',
+  'mts',
+]);
 
 export const thumbnailKind = (name: string): 'image' | 'video' | null => {
   const ext = extname(name).slice(1).toLowerCase();