diff --git a/Python Version/pymosh/codec/mpeg4.py b/Python Version/pymosh/codec/mpeg4.py
new file mode 100644
index 0000000..3e4952d
--- /dev/null
+++ b/Python Version/pymosh/codec/mpeg4.py	
@@ -0,0 +1,6 @@
+IFRAME_HEADER = b'\x00\x00\x01\xb0'
+
+
+def is_iframe(frame):
+    """Determine whether frame is an I frame."""
+    return frame[:4] == IFRAME_HEADER