diff --git a/main.py b/main.py
index 0661efc..0724973 100644
--- a/main.py
+++ b/main.py
@@ -1,7 +1,19 @@
+import os
 import sys
 from PyQt6.QtWidgets import QApplication, QMainWindow
 
 
+def build_export_path(folder: str, basename: str, counter: int) -> str:
+    filename = f"{basename}_{counter:03d}.mp4"
+    return os.path.join(folder, filename)
+
+
+def format_time(seconds: float) -> str:
+    m = int(seconds) // 60
+    s = seconds - m * 60
+    return f"{m}:{s:04.1f}"
+
+
 def main():
     app = QApplication(sys.argv)
     win = MainWindow()
diff --git a/tests/test_utils.py b/tests/test_utils.py
index e69de29..75a10ae 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -0,0 +1,22 @@
+import sys, os
+sys.path.insert(0, os.path.dirname(os.path.dirname(__file__)))
+from main import build_export_path, format_time
+
+
+def test_build_export_path_first():
+    assert build_export_path("/out", "clip", 1) == "/out/clip_001.mp4"
+
+def test_build_export_path_counter():
+    assert build_export_path("/out", "clip", 42) == "/out/clip_042.mp4"
+
+def test_build_export_path_deep_counter():
+    assert build_export_path("/out", "shot", 999) == "/out/shot_999.mp4"
+
+def test_format_time_seconds():
+    assert format_time(0.0) == "0:00.0"
+
+def test_format_time_minutes():
+    assert format_time(75.3) == "1:15.3"
+
+def test_format_time_rounding():
+    assert format_time(61.05) == "1:01.0"