Process videos on web with WebCodecs (#10955)

Co-authored-by: Samuel Newman <mozzius@protonmail.com>

src/view/com/composer/videos/VideoTranscodeBackdrop.web.tsx

@@ -1,7 +1,26 @@
+import {atoms as a, flatten} from '#/alf'
+
 export function clearThumbnailCache() {
-  // no-op
+  // no-op on web
 }
 
-export function VideoTranscodeBackdrop() {
-  return null
+export function VideoTranscodeBackdrop({uri}: {uri: string}) {
+  return (
+    <video
+      src={uri}
+      style={flatten([
+        a.absolute,
+        a.inset_0,
+        a.h_full,
+        a.w_full,
+        {
+          objectFit: 'cover',
+          filter: 'blur(15px)',
+          transform: 'scale(1.1)', // hide blur edges
+        },
+      ])}
+      muted
+      playsInline
+    />
+  )
 }