fixes (maybe) video preview after render on firefox

src/App.svelte

@@ -54,6 +54,11 @@
       const data = await ffmpeg.readFile(outname);
       rendering = false;
       videoValue = URL.createObjectURL(new Blob([data.buffer], { type: "video/mp4" }));
+      if (outname.endsWith("mp4")) {
+        setTimeout(() => {
+          vidPlayerRef.seekToNextFrame();
+        }, 100);
+      }
     } catch (e) {
       log += e + "\n";
     }