From 5a7ea12182385ab0e751b8b73a4f9942de28148c Mon Sep 17 00:00:00 2001
From: Jo Turk <git@joturk.net>
Date: Sat, 31 Jan 2026 17:14:48 +0200
Subject: [PATCH] Do not validate non spec obu-size

---
 codecs/av1_depacketizer.go      | 31 ++++++++++++++++++++-----------
 codecs/av1_depacketizer_test.go | 24 ++++++++++++++++++++----
 2 files changed, 40 insertions(+), 15 deletions(-)

diff --git a/codecs/av1_depacketizer.go b/codecs/av1_depacketizer.go
index d9dbbcd..8b04e49 100644
--- a/codecs/av1_depacketizer.go
+++ b/codecs/av1_depacketizer.go
@@ -21,6 +21,20 @@ type AV1Depacketizer struct {
 	videoDepacketizer
 }
 
+func (d *AV1Depacketizer) appendOBUWithCalculatedSize(
+	buff []byte,
+	obuHeader *obu.Header,
+	obuBuffer []byte,
+	payloadOffset int,
+) []byte {
+	obuPayloadSize := len(obuBuffer) - payloadOffset
+	buff = append(buff, obuHeader.Marshal()...)
+	buff = append(buff, obu.WriteToLeb128(uint(obuPayloadSize))...) // nolint: gosec // G104
+	buff = append(buff, obuBuffer[payloadOffset:]...)
+
+	return buff
+}
+
 // Unmarshal parses an AV1 RTP payload into its constituent OBUs stream with obu_size_field,
 // It assumes that the payload is in order (e.g. the caller is responsible for reordering RTP packets).
 // If the last OBU in the payload is fragmented, it will be stored in the buffer until the
@@ -144,22 +158,17 @@ func (d *AV1Depacketizer) Unmarshal(payload []byte) (buff []byte, err error) {
 				return nil, err
 			}
 
-			// We validate the obu_size_field if it is present.
+			// Ignore obu_size_field if it is present and doesn't match the calculated size.
 			sizeFromOBUSize := obuHeader.Size() + int(obuSize) + int(n) //nolint:gosec
 			if lengthField != sizeFromOBUSize {
-				return nil, fmt.Errorf(
-					"%w: OBU size %d does not match calculated size %d",
-					errShortPacket, obuSize, sizeFromOBUSize,
-				)
+				payloadOffset := obuHeader.Size() + int(n) //nolint:gosec // n is small, LEB128.
+				buff = d.appendOBUWithCalculatedSize(buff, obuHeader, obuBuffer, payloadOffset)
+			} else {
+				buff = append(buff, obuBuffer...)
 			}
-
-			buff = append(buff, obuBuffer...)
 		} else {
 			obuHeader.HasSizeField = true
-			buff = append(buff, obuHeader.Marshal()...)
-			size := len(obuBuffer) - obuHeader.Size()
-			buff = append(buff, obu.WriteToLeb128(uint(size))...) // nolint: gosec // G104
-			buff = append(buff, obuBuffer[obuHeader.Size():]...)
+			buff = d.appendOBUWithCalculatedSize(buff, obuHeader, obuBuffer, obuHeader.Size())
 		}
 
 		if isLast {
diff --git a/codecs/av1_depacketizer_test.go b/codecs/av1_depacketizer_test.go
index 2fd725c..bdfa00e 100644
--- a/codecs/av1_depacketizer_test.go
+++ b/codecs/av1_depacketizer_test.go
@@ -114,6 +114,7 @@ func TestAV1Depacketizer_validateOBUSize(t *testing.T) {
 	tests := []struct {
 		name    string
 		payload []byte
+		expect  []byte
 		err     error
 	}{
 		{
@@ -135,7 +136,11 @@ func TestAV1Depacketizer_validateOBUSize(t *testing.T) {
 				0x04,             // LEB128 size
 				0x03, 0x01, 0x02, // OBU data
 			},
-			err: errShortPacket,
+			expect: []byte{
+				0x22,             // OBU header
+				0x03,             // Corrected size
+				0x03, 0x01, 0x02, // OBU data
+			},
 		},
 		{
 			name: "OBU size smaller than length field",
@@ -146,15 +151,26 @@ func TestAV1Depacketizer_validateOBUSize(t *testing.T) {
 				0x02,             // LEB128 size
 				0x03, 0x01, 0x02, // OBU data
 			},
-			err: errShortPacket,
+			expect: []byte{
+				0x22,             // OBU header
+				0x03,             // Corrected size
+				0x03, 0x01, 0x02, // OBU data
+			},
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			d := AV1Depacketizer{}
-			_, err := d.Unmarshal(tt.payload)
-			assert.ErrorIs(t, err, tt.err)
+			obu, err := d.Unmarshal(tt.payload)
+			if tt.err != nil {
+				assert.ErrorIs(t, err, tt.err)
+
+				return
+			}
+
+			assert.NoError(t, err)
+			assert.Equal(t, tt.expect, obu)
 		})
 	}
 }