mpeg4audio: support all ADTS profiles (#275)

ADTS supports profiles 0-3 per ISO 14496-3, mapping to ObjectType 1-4.
Previously only ObjectType 2 (AAC-LC) was accepted, rejecting valid
streams with AAC Main (1), AAC SSR (3), or AAC LTP (4).

---------

Co-authored-by: aler9 <46489434+aler9@users.noreply.github.com>

pkg/codecs/mpeg4audio/adts.go

@@ -38,12 +38,9 @@ func (ps *ADTSPackets) Unmarshal(buf []byte) error {
 
 		pkt := &ADTSPacket{}
 
+		// ADTS profile (2 bits) maps to ObjectType = profile + 1
+		// All profiles 0-3 are valid per ISO 14496-3
 		pkt.Type = ObjectType((buf[pos+2] >> 6) + 1)
-		switch pkt.Type {
-		case ObjectTypeAACLC:
-		default:
-			return fmt.Errorf("unsupported audio type: %d", pkt.Type)
-		}
 
 		sampleRateIndex := (buf[pos+2] >> 2) & 0x0F
 		switch {
@@ -114,6 +111,11 @@ func (ps ADTSPackets) Marshal() ([]byte, error) {
 	pos := 0
 
 	for _, pkt := range ps {
+		// ADTS only supports ObjectType 1-4 (profile 0-3)
+		if pkt.Type < 1 || pkt.Type > 4 {
+			return nil, fmt.Errorf("ADTS only supports ObjectType 1-4, got %d", pkt.Type)
+		}
+
 		sampleRateIndex, ok := reverseSampleRates[pkt.SampleRate]
 		if !ok {
 			return nil, fmt.Errorf("invalid sample rate: %d", pkt.SampleRate)

pkg/codecs/mpeg4audio/adts_test.go

@@ -45,6 +45,18 @@ var casesADTS = []struct {
 			},
 		},
 	},
+	{
+		"aac-ssr",
+		[]byte{0xff, 0xf1, 0x8c, 0x80, 0x1, 0x3f, 0xfc, 0xaa, 0xbb},
+		ADTSPackets{
+			{
+				Type:         3,
+				SampleRate:   48000,
+				ChannelCount: 2,
+				AU:           []byte{0xaa, 0xbb},
+			},
+		},
+	},
 }
 
 func TestADTSUnmarshal(t *testing.T) {