diff --git a/src/webrtc.rs b/src/webrtc.rs
index 380d315..eaa012e 100644
--- a/src/webrtc.rs
+++ b/src/webrtc.rs
@@ -520,16 +520,17 @@ fn local_ip() -> Option<String> {
 
 fn is_idr_nalu(data: &[u8]) -> bool {
     let mut i = 0;
-    while i + 4 < data.len() {
-        if data[i..i + 4] == [0, 0, 0, 1] {
-            let nal_type = data[i + 4] & 0x1F;
-            if nal_type == 5 {
+    while i < data.len() {
+        let tail = &data[i..];
+        if tail.starts_with(&[0, 0, 0, 1]) {
+            let Some(&header) = tail.get(4) else { break };
+            if header & 0x1F == 5 {
                 return true;
             }
             i += 5;
-        } else if i + 3 < data.len() && data[i..i + 3] == [0, 0, 1] {
-            let nal_type = data[i + 3] & 0x1F;
-            if nal_type == 5 {
+        } else if tail.starts_with(&[0, 0, 1]) {
+            let Some(&header) = tail.get(3) else { break };
+            if header & 0x1F == 5 {
                 return true;
             }
             i += 4;
@@ -539,3 +540,78 @@ fn is_idr_nalu(data: &[u8]) -> bool {
     }
     false
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn empty_data() {
+        assert!(!is_idr_nalu(&[]));
+    }
+
+    #[test]
+    fn short_data_no_start_code() {
+        assert!(!is_idr_nalu(&[0]));
+        assert!(!is_idr_nalu(&[0, 0]));
+        assert!(!is_idr_nalu(&[1, 2, 3]));
+    }
+
+    #[test]
+    fn three_byte_start_code_no_nal_header() {
+        assert!(!is_idr_nalu(&[0, 0, 1]));
+    }
+
+    #[test]
+    fn four_byte_start_code_no_nal_header() {
+        assert!(!is_idr_nalu(&[0, 0, 0, 1]));
+    }
+
+    #[test]
+    fn three_byte_start_code_idr_at_tail() {
+        assert!(is_idr_nalu(&[0, 0, 1, 0x65]));
+        assert!(!is_idr_nalu(&[0, 0, 1, 0x01]));
+    }
+
+    #[test]
+    fn four_byte_start_code_idr_at_tail() {
+        assert!(is_idr_nalu(&[0, 0, 0, 1, 0x65]));
+        assert!(!is_idr_nalu(&[0, 0, 0, 1, 0x01]));
+    }
+
+    #[test]
+    fn idr_in_middle_of_frame() {
+        let data: Vec<u8> = [
+            &[0, 0, 0, 1, 0x67][..], // SPS
+            &[0, 0, 0, 1, 0x68][..], // PPS
+            &[0, 0, 0, 1, 0x65][..], // IDR
+        ]
+        .concat();
+        assert!(is_idr_nalu(&data));
+    }
+
+    #[test]
+    fn no_idr_in_frame() {
+        let data: Vec<u8> = [
+            &[0, 0, 0, 1, 0x67][..], // SPS
+            &[0, 0, 0, 1, 0x68][..], // PPS
+        ]
+        .concat();
+        assert!(!is_idr_nalu(&data));
+    }
+
+    #[test]
+    fn mixed_start_code_lengths() {
+        let data: Vec<u8> = [
+            &[0, 0, 0, 1, 0x67][..], // SPS (4-byte start code)
+            &[0, 0, 1, 0x65][..],    // IDR (3-byte start code)
+        ]
+        .concat();
+        assert!(is_idr_nalu(&data));
+    }
+
+    #[test]
+    fn all_zeros() {
+        assert!(!is_idr_nalu(&[0, 0, 0, 0, 0, 0, 0, 0]));
+    }
+}