h264: support empty NALUs inside AVCC

(bluenviron/mediamtx#2375)
bluenviron · Sep 24, 2023 · 5354429 · 5354429
1 parent 7fae03f
commit 5354429
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Showing 3 changed files with 45 additions and 19 deletions.
diff --git a/README.md b/README.md
@@ -21,6 +21,7 @@ Definitions and functions shared between [gortsplib](https://github.com/bluenvir
 |[ITU-T Rec. T-871, JPEG File Interchange Format](https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-T.871-201105-I!!PDF-E&type=items)|JPEG codec|
 |[ITU-T Rec. H.264 (08/2021)](https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.264-202108-I!!PDF-E&type=items)|H264 codec|
 |[ITU-T Rec. H.265 (08/2021)](https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.265-202108-I!!PDF-E&type=items)|H265 codec|
+|ISO 14496-15, Coding of audio-visual objects, Part 15, Advanced Video Coding (AVC) file format|H264 and H265 inside MP4|
 |[VP9 Bitstream & Decoding Process Specification v0.6](https://storage.googleapis.com/downloads.webmproject.org/docs/vp9/vp9-bitstream-specification-v0.6-20160331-draft.pdf)|VP9 codec|
 |[VP9 Codec ISO Media File Format Binding](https://www.webmproject.org/vp9/mp4/)|VP9 inside MP4|
 |[AV1 Bitstream & Decoding Process](https://aomediacodec.github.io/av1-spec/av1-spec.pdf)|AV1 codec|

diff --git a/pkg/codecs/h264/avcc.go b/pkg/codecs/h264/avcc.go
@@ -1,11 +1,15 @@
 package h264
 
 import (
+	"errors"
 	"fmt"
 )
 
+// ErrAVCCNoNALUs is returned by AVCCUnmarshal when no NALUs have been decoded.
+var ErrAVCCNoNALUs = errors.New("AVCC unit doesn't contain any NALU")
+
 // AVCCUnmarshal decodes an access unit from the AVCC stream format.
-// Specification: ?
+// Specification: ISO 14496-15, section 5.3.4.2.1
 func AVCCUnmarshal(buf []byte) ([][]byte, error) {
 	bl := len(buf)
 	pos := 0
@@ -21,33 +25,35 @@ func AVCCUnmarshal(buf []byte) ([][]byte, error) {
 		l := int(uint32(buf[pos])<<24 | uint32(buf[pos+1])<<16 | uint32(buf[pos+2])<<8 | uint32(buf[pos+3]))
 		pos += 4
 
-		if l == 0 {
-			return nil, fmt.Errorf("invalid NALU")
-		}
+		if l != 0 {
+			if (auSize + l) > MaxAccessUnitSize {
+				return nil, fmt.Errorf("access unit size (%d) is too big, maximum is %d", auSize+l, MaxAccessUnitSize)
+			}
 
-		if (auSize + l) > MaxAccessUnitSize {
-			return nil, fmt.Errorf("access unit size (%d) is too big, maximum is %d", auSize+l, MaxAccessUnitSize)
-		}
+			if (naluCount + 1) > MaxNALUsPerAccessUnit {
+				return nil, fmt.Errorf("NALU count (%d) exceeds maximum allowed (%d)",
+					len(ret)+1, MaxNALUsPerAccessUnit)
+			}
 
-		if (naluCount + 1) > MaxNALUsPerAccessUnit {
-			return nil, fmt.Errorf("NALU count (%d) exceeds maximum allowed (%d)",
-				len(ret)+1, MaxNALUsPerAccessUnit)
-		}
+			if (bl - pos) < l {
+				return nil, fmt.Errorf("invalid length")
+			}
 
-		if (bl - pos) < l {
-			return nil, fmt.Errorf("invalid length")
+			ret = append(ret, buf[pos:pos+l])
+			auSize += l
+			naluCount++
+			pos += l
 		}
 
-		ret = append(ret, buf[pos:pos+l])
-		auSize += l
-		naluCount++
-		pos += l
-
 		if (bl - pos) == 0 {
 			break
 		}
 	}
 
+	if ret == nil {
+		return nil, ErrAVCCNoNALUs
+	}
+
 	return ret, nil
 }
 
@@ -60,7 +66,7 @@ func avccMarshalSize(au [][]byte) int {
 }
 
 // AVCCMarshal encodes an access unit into the AVCC stream format.
-// Specification: ?
+// Specification: ISO 14496-15, section 5.3.4.2.1
 func AVCCMarshal(au [][]byte) ([]byte, error) {
 	buf := make([]byte, avccMarshalSize(au))
 	pos := 0

diff --git a/pkg/codecs/h264/avcc_test.go b/pkg/codecs/h264/avcc_test.go
@@ -49,6 +49,25 @@ func TestAVCCUnmarshal(t *testing.T) {
 	}
 }
 
+// issue mediamtx/2375
+func TestAVCCUnmarshalEmpty(t *testing.T) {
+	dec, err := AVCCUnmarshal([]byte{
+		0x0, 0x0, 0x0, 0x0,
+	})
+
+	require.Equal(t, ErrAVCCNoNALUs, err)
+	require.Equal(t, [][]byte(nil), dec)
+
+	dec, err = AVCCUnmarshal([]byte{
+		0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x3, 0x1, 0x2, 0x3,
+	})
+
+	require.NoError(t, err)
+	require.Equal(t, [][]byte{
+		{1, 2, 3},
+	}, dec)
+}
+
 func TestAVCCMarshal(t *testing.T) {
 	for _, ca := range casesAVCC {
 		t.Run(ca.name, func(t *testing.T) {