diff --git a/core/webrtc/keyframecache.go b/core/webrtc/keyframecache.go
index 83caeb7..9227f04 100644
--- a/core/webrtc/keyframecache.go
+++ b/core/webrtc/keyframecache.go
@@ -38,15 +38,15 @@ func newKeyFrameCache() *keyFrameCache {
 }
 
 // isH264IDRStart returns true if pkt begins an H.264 IDR (keyframe)
-// NAL. It recognises:
+// NAL. It recognises three RFC 6184 packetisation modes:
 //
-//   - Single NAL unit packets where NAL type == 5 (IDR slice).
-//   - FU-A fragments with the start bit set and inner NAL type == 5.
-//
-// STAP-A aggregates that happen to lead with an IDR NAL are not
-// detected here; in practice FFmpeg and GStreamer never use STAP-A for
-// IDR slices because the slices are too large. If that assumption
-// changes, add STAP-A handling in a future revision.
+//   - Single NAL unit (type 5): the entire payload is one IDR slice.
+//   - FU-A fragment (type 28): the FU header byte has the start bit set
+//     (0x80) and the inner NAL type is 5.
+//   - STAP-A aggregate (type 24): the first NAL in the aggregate is an
+//     IDR slice. STAP-A format: byte 0 = NAL header (type 24), bytes
+//     1–2 = first NAL size (big-endian uint16), byte 3 = first NAL
+//     header. Minimum valid payload: 4 bytes.
 func isH264IDRStart(pkt *rtp.Packet) bool {
 	p := pkt.Payload
 	if len(p) == 0 {
@@ -56,6 +56,8 @@ func isH264IDRStart(pkt *rtp.Packet) bool {
 	switch nalType {
 	case 5: // Single NAL unit, IDR slice
 		return true
+	case 24: // STAP-A — bytes 1–2 are the first NAL's size; byte 3 is its header
+		return len(p) >= 4 && p[3]&0x1F == 5
 	case 28: // FU-A — byte 1 is the FU header: bit 7 = start, bits 4–0 = inner type
 		return len(p) >= 2 && p[1]&0x80 != 0 && p[1]&0x1F == 5
 	}