add resetFragments() to all fragment-based decoders (#637)

pkg/format/rtpac3/decoder.go

@@ -42,12 +42,16 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 // Decode decodes frames from a RTP packet.
 // It returns the frames and the PTS of the first frame.
 func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 	if len(pkt.Payload) < 2 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("payload is too short")
 	}
 
@@ -55,8 +59,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 	ft := pkt.Payload[0] & 0b11
 
 	if mbz != 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("invalid MBZ: %v", mbz)
 	}
 
@@ -64,8 +67,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 
 	switch ft {
 	case 0:
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		d.firstPacketReceived = true
 
 		buf := pkt.Payload[2:]
@@ -91,8 +93,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 		}
 
 	case 1, 2:
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 
 		var syncInfo ac3.SyncInfo
 		err := syncInfo.Unmarshal(pkt.Payload[2:])
@@ -122,8 +123,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 		d.fragmentsExpected -= le
 
 		if d.fragmentsExpected < 0 {
-			d.fragments = d.fragments[:0] // discard pending fragments
-			d.fragmentsSize = 0
+			d.resetFragments()
 			return nil, fmt.Errorf("fragment is too big")
 		}
 
@@ -134,8 +134,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 		}
 
 		frames = [][]byte{joinFragments(d.fragments, d.fragmentsSize)}
-		d.fragments = d.fragments[:0]
-		d.fragmentsSize = 0
+		d.resetFragments()
 	}
 
 	return frames, nil

pkg/format/rtpav1/decoder.go

@@ -46,17 +46,21 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 func (d *Decoder) decodeOBUs(pkt *rtp.Packet) ([][]byte, error) {
 	var av1header codecs.AV1Packet
 	_, err := av1header.Unmarshal(pkt.Payload)
 	if err != nil {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("invalid header: %w", err)
 	}
 
 	if av1header.Z {
-		if len(d.fragments) == 0 {
+		if d.fragmentsSize == 0 {
 			if !d.firstPacketReceived {
 				return nil, ErrNonStartingPacketAndNoPrevious
 			}
@@ -66,8 +70,7 @@ func (d *Decoder) decodeOBUs(pkt *rtp.Packet) ([][]byte, error) {
 
 		d.fragmentsSize += len(av1header.OBUElements[0])
 		if d.fragmentsSize > av1.MaxTemporalUnitSize {
-			d.fragments = d.fragments[:0]
-			d.fragmentsSize = 0
+			d.resetFragments()
 			return nil, fmt.Errorf("OBU size (%d) is too big, maximum is %d", d.fragmentsSize, av1.MaxTemporalUnitSize)
 		}
 
@@ -82,17 +85,16 @@ func (d *Decoder) decodeOBUs(pkt *rtp.Packet) ([][]byte, error) {
 	if len(av1header.OBUElements) > 0 {
 		if d.fragmentsSize != 0 {
 			obus = append(obus, joinFragments(d.fragments, d.fragmentsSize))
-			d.fragments = d.fragments[:0]
-			d.fragmentsSize = 0
+			d.resetFragments()
 		}
 
 		if av1header.Y {
 			elementCount := len(av1header.OBUElements)
 
 			d.fragmentsSize += len(av1header.OBUElements[elementCount-1])
+
 			if d.fragmentsSize > av1.MaxTemporalUnitSize {
-				d.fragments = d.fragments[:0]
-				d.fragmentsSize = 0
+				d.resetFragments()
 				return nil, fmt.Errorf("OBU size (%d) is too big, maximum is %d", d.fragmentsSize, av1.MaxTemporalUnitSize)
 			}
 
@@ -103,8 +105,7 @@ func (d *Decoder) decodeOBUs(pkt *rtp.Packet) ([][]byte, error) {
 		obus = append(obus, av1header.OBUElements...)
 	} else if !av1header.Y {
 		obus = append(obus, joinFragments(d.fragments, d.fragmentsSize))
-		d.fragments = d.fragments[:0]
-		d.fragmentsSize = 0
+		d.resetFragments()
 	}
 
 	if len(obus) == 0 {

pkg/format/rtph264/decoder.go

@@ -63,9 +63,14 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 	if len(pkt.Payload) < 1 {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		return nil, fmt.Errorf("payload is too short")
 	}
 
@@ -82,7 +87,7 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 		end := (pkt.Payload[1] >> 6) & 0x01
 
 		if start == 1 {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 
 			if end != 0 {
 				return nil, fmt.Errorf("invalid FU-A packet (can't contain both a start and end bit)")
@@ -97,7 +102,7 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 			return nil, ErrMorePacketsNeeded
 		}
 
-		if len(d.fragments) == 0 {
+		if d.fragmentsSize == 0 {
 			if !d.firstPacketReceived {
 				return nil, ErrNonStartingPacketAndNoPrevious
 			}
@@ -108,7 +113,7 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 		d.fragmentsSize += len(pkt.Payload[2:])
 
 		if d.fragmentsSize > h264.MaxAccessUnitSize {
-			d.fragments = d.fragments[:0]
+			d.resetFragments()
 			return nil, fmt.Errorf("NALU size (%d) is too big, maximum is %d", d.fragmentsSize, h264.MaxAccessUnitSize)
 		}
 
@@ -119,10 +124,10 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 		}
 
 		nalus = [][]byte{joinFragments(d.fragments, d.fragmentsSize)}
-		d.fragments = d.fragments[:0]
+		d.resetFragments()
 
 	case h264.NALUTypeSTAPA:
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 
 		payload := pkt.Payload[1:]
 
@@ -159,12 +164,12 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 
 	case h264.NALUTypeSTAPB, h264.NALUTypeMTAP16,
 		h264.NALUTypeMTAP24, h264.NALUTypeFUB:
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		d.firstPacketReceived = true
 		return nil, fmt.Errorf("packet type not supported (%v)", typ)
 
 	default:
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		d.firstPacketReceived = true
 		nalus = [][]byte{pkt.Payload}
 	}

pkg/format/rtph265/decoder.go

@@ -35,8 +35,8 @@ type Decoder struct {
 	MaxDONDiff int
 
 	firstPacketReceived bool
-	fragmentsSize       int
 	fragments           [][]byte
+	fragmentsSize       int
 
 	// for Decode()
 	frameBuffer     [][]byte
@@ -52,9 +52,14 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 	if len(pkt.Payload) < 2 {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		return nil, fmt.Errorf("payload is too short")
 	}
 
@@ -63,7 +68,7 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 
 	switch typ {
 	case h265.NALUType_AggregationUnit:
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 
 		payload := pkt.Payload[2:]
 
@@ -95,7 +100,7 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 
 	case h265.NALUType_FragmentationUnit:
 		if len(pkt.Payload) < 3 {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 			return nil, fmt.Errorf("payload is too short")
 		}
 
@@ -103,7 +108,7 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 		end := (pkt.Payload[2] >> 6) & 0x01
 
 		if start == 1 {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 
 			if end != 0 {
 				return nil, fmt.Errorf("invalid fragmentation unit (can't contain both a start and end bit)")
@@ -118,7 +123,7 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 			return nil, ErrMorePacketsNeeded
 		}
 
-		if len(d.fragments) == 0 {
+		if d.fragmentsSize == 0 {
 			if !d.firstPacketReceived {
 				return nil, ErrNonStartingPacketAndNoPrevious
 			}
@@ -128,7 +133,7 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 
 		d.fragmentsSize += len(pkt.Payload[3:])
 		if d.fragmentsSize > h265.MaxAccessUnitSize {
-			d.fragments = d.fragments[:0]
+			d.resetFragments()
 			return nil, fmt.Errorf("NALU size (%d) is too big, maximum is %d", d.fragmentsSize, h265.MaxAccessUnitSize)
 		}
 
@@ -139,16 +144,14 @@ func (d *Decoder) decodeNALUs(pkt *rtp.Packet) ([][]byte, error) {
 		}
 
 		nalus = [][]byte{joinFragments(d.fragments, d.fragmentsSize)}
-		d.fragments = d.fragments[:0]
+		d.resetFragments()
 
 	case h265.NALUType_PACI:
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.firstPacketReceived = true
+		d.resetFragments()
 		return nil, fmt.Errorf("PACI packets are not supported (yet)")
 
 	default:
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.firstPacketReceived = true
+		d.resetFragments()
 		nalus = [][]byte{pkt.Payload}
 	}
 

pkg/format/rtpmjpeg/decoder.go

@@ -163,8 +163,8 @@ func joinFragments(fragments [][]byte, size int) []byte {
 // Specification: https://datatracker.ietf.org/doc/html/rfc2435
 type Decoder struct {
 	firstPacketReceived bool
-	fragmentsSize       int
 	fragments           [][]byte
+	fragmentsSize       int
 	firstJpegHeader     *headerJPEG
 	quantizationTables  [][]byte
 }
@@ -174,6 +174,11 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 // Decode decodes an image from a RTP packet.
 func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 	byts := pkt.Payload
@@ -194,8 +199,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 	}
 
 	if jh.FragmentOffset == 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		d.firstPacketReceived = true
 
 		if jh.Quantization >= 128 {
@@ -219,8 +223,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 				return nil, ErrNonStartingPacketAndNoPrevious
 			}
 
-			d.fragments = d.fragments[:0] // discard pending fragments
-			d.fragmentsSize = 0
+			d.resetFragments()
 			return nil, fmt.Errorf("received wrong fragment")
 		}
 
@@ -237,8 +240,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 	}
 
 	data := joinFragments(d.fragments, d.fragmentsSize)
-	d.fragments = d.fragments[:0]
-	d.fragmentsSize = 0
+	d.resetFragments()
 
 	var buf []byte
 

pkg/format/rtpmpeg1audio/decoder.go

@@ -41,18 +41,21 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 // Decode decodes frames from a RTP packet.
 func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 	if len(pkt.Payload) < 5 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("payload is too short")
 	}
 
 	mbz := uint16(pkt.Payload[0])<<8 | uint16(pkt.Payload[1])
 	if mbz != 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("invalid MBZ: %v", mbz)
 	}
 
@@ -61,8 +64,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 	var frames [][]byte
 
 	if offset == 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		d.firstPacketReceived = true
 
 		buf := pkt.Payload[4:]
@@ -98,8 +100,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 				return nil, ErrNonStartingPacketAndNoPrevious
 			}
 
-			d.fragments = d.fragments[:0] // discard pending fragments
-			d.fragmentsSize = 0
+			d.resetFragments()
 			return nil, fmt.Errorf("unexpected offset %v, expected %v", offset, d.fragmentsSize)
 		}
 
@@ -108,8 +109,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 		d.fragmentsExpected -= bl
 
 		if d.fragmentsExpected < 0 {
-			d.fragments = d.fragments[:0] // discard pending fragments
-			d.fragmentsSize = 0
+			d.resetFragments()
 			return nil, fmt.Errorf("fragment is too big")
 		}
 
@@ -120,8 +120,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 		}
 
 		frames = [][]byte{joinFragments(d.fragments, d.fragmentsSize)}
-		d.fragments = d.fragments[:0]
-		d.fragmentsSize = 0
+		d.resetFragments()
 	}
 
 	return frames, nil

pkg/format/rtpmpeg1video/decoder.go

@@ -45,38 +45,38 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 func (d *Decoder) decodeSlice(pkt *rtp.Packet) ([]byte, error) {
 	if len(pkt.Payload) < 4 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("payload is too short")
 	}
 
 	mbz := pkt.Payload[0] >> 3
 	if mbz != 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("invalid MBZ: %v", mbz)
 	}
 
 	t := (pkt.Payload[0] >> 2) & 0x01
 	if t != 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("MPEG-2 video-specific header extension is not supported yet")
 	}
 
 	an := pkt.Payload[2] >> 7
 	if an != 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("AN not supported yet")
 	}
 
 	n := (pkt.Payload[2] >> 6) & 0x01
 	if n != 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("N not supported yet")
 	}
 
@@ -88,7 +88,7 @@ func (d *Decoder) decodeSlice(pkt *rtp.Packet) ([]byte, error) {
 		return pkt.Payload[4:], nil
 
 	case b == 1:
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.fragments = d.fragments[:0]
 		d.fragments = append(d.fragments, pkt.Payload[4:])
 		d.fragmentsSize = len(pkt.Payload[4:])
 		return nil, ErrMorePacketsNeeded
@@ -102,8 +102,7 @@ func (d *Decoder) decodeSlice(pkt *rtp.Packet) ([]byte, error) {
 		d.fragmentsSize += len(pkt.Payload[4:])
 
 		slice := joinFragments(d.fragments, d.fragmentsSize)
-		d.fragments = d.fragments[:0]
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return slice, nil
 
 	default:

pkg/format/rtpmpeg4audio/decoder.go

@@ -45,6 +45,11 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 // Decode decodes AUs from a RTP packet.
 // It returns the AUs and the PTS of the first AU.
 // The PTS of subsequent AUs can be calculated by adding time.Second*mpeg4audio.SamplesPerAccessUnit/clockRate.

pkg/format/rtpmpeg4audio/decoder_generic.go

@@ -10,14 +10,14 @@ import (
 
 func (d *Decoder) decodeGeneric(pkt *rtp.Packet) ([][]byte, error) {
 	if len(pkt.Payload) < 2 {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		return nil, fmt.Errorf("payload is too short")
 	}
 
 	// AU-headers-length (16 bits)
 	headersLen := int(uint16(pkt.Payload[0])<<8 | uint16(pkt.Payload[1]))
 	if headersLen == 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		return nil, fmt.Errorf("invalid AU-headers-length")
 	}
 	payload := pkt.Payload[2:]
@@ -25,7 +25,7 @@ func (d *Decoder) decodeGeneric(pkt *rtp.Packet) ([][]byte, error) {
 	// AU-headers
 	dataLens, err := d.readAUHeaders(payload, headersLen)
 	if err != nil {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		return nil, err
 	}
 
@@ -37,7 +37,7 @@ func (d *Decoder) decodeGeneric(pkt *rtp.Packet) ([][]byte, error) {
 
 	var aus [][]byte
 
-	if len(d.fragments) == 0 {
+	if d.fragmentsSize == 0 {
 		if pkt.Marker {
 			// AUs
 			aus = make([][]byte, len(dataLens))
@@ -65,18 +65,18 @@ func (d *Decoder) decodeGeneric(pkt *rtp.Packet) ([][]byte, error) {
 	} else {
 		// we are decoding a fragmented AU
 		if len(dataLens) != 1 {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 			return nil, fmt.Errorf("a fragmented packet can only contain one AU")
 		}
 
 		if len(payload) < int(dataLens[0]) {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 			return nil, fmt.Errorf("payload is too short")
 		}
 
 		d.fragmentsSize += int(dataLens[0])
 		if d.fragmentsSize > mpeg4audio.MaxAccessUnitSize {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 			return nil, fmt.Errorf("access unit size (%d) is too big, maximum is %d",
 				d.fragmentsSize, mpeg4audio.MaxAccessUnitSize)
 		}
@@ -88,7 +88,7 @@ func (d *Decoder) decodeGeneric(pkt *rtp.Packet) ([][]byte, error) {
 		}
 
 		aus = [][]byte{joinFragments(d.fragments, d.fragmentsSize)}
-		d.fragments = d.fragments[:0]
+		d.resetFragments()
 	}
 
 	return d.removeADTS(aus)

pkg/format/rtpmpeg4audio/decoder_latm.go

@@ -11,7 +11,7 @@ func (d *Decoder) decodeLATM(pkt *rtp.Packet) ([][]byte, error) {
 	var au []byte
 	buf := pkt.Payload
 
-	if len(d.fragments) == 0 {
+	if d.fragmentsSize == 0 {
 		pl, n, err := payloadLengthInfoDecode(buf)
 		if err != nil {
 			return nil, err
@@ -25,7 +25,7 @@ func (d *Decoder) decodeLATM(pkt *rtp.Packet) ([][]byte, error) {
 			// there could be other data, due to otherDataPresent. Ignore it.
 		} else {
 			if pl > mpeg4audio.MaxAccessUnitSize {
-				d.fragments = d.fragments[:0] // discard pending fragments
+				d.resetFragments()
 				return nil, fmt.Errorf("access unit size (%d) is too big, maximum is %d",
 					pl, mpeg4audio.MaxAccessUnitSize)
 			}
@@ -48,7 +48,7 @@ func (d *Decoder) decodeLATM(pkt *rtp.Packet) ([][]byte, error) {
 		// there could be other data, due to otherDataPresent. Ignore it.
 
 		au = joinFragments(d.fragments, d.fragmentsSize)
-		d.fragments = d.fragments[:0]
+		d.resetFragments()
 	}
 
 	return [][]byte{au}, nil

pkg/format/rtpmpeg4video/decoder.go

@@ -33,11 +33,16 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 // Decode decodes a frame from a RTP packet.
 func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 	var frame []byte
 
-	if len(d.fragments) == 0 {
+	if d.fragmentsSize == 0 {
 		if pkt.Marker {
 			frame = pkt.Payload
 		} else {
@@ -48,7 +53,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 	} else {
 		d.fragmentsSize += len(pkt.Payload)
 		if d.fragmentsSize > mpeg4video.MaxFrameSize {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 			return nil, fmt.Errorf("frame size (%d) is too big, maximum is %d", d.fragmentsSize, mpeg4video.MaxFrameSize)
 		}
 
@@ -59,7 +64,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 		}
 
 		frame = joinFragments(d.fragments, d.fragmentsSize)
-		d.fragments = d.fragments[:0]
+		d.resetFragments()
 	}
 
 	return frame, nil

pkg/format/rtpvp8/decoder.go

@@ -41,24 +41,29 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 // Decode decodes a VP8 frame from a RTP packet.
 func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 	var vpkt codecs.VP8Packet
 	_, err := vpkt.Unmarshal(pkt.Payload)
 	if err != nil {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		return nil, err
 	}
 
 	if vpkt.PID != 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		return nil, fmt.Errorf("packets containing single partitions are not supported")
 	}
 
 	var frame []byte
 
 	if vpkt.S == 1 {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		d.firstPacketReceived = true
 
 		if !pkt.Marker {
@@ -69,7 +74,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 
 		frame = vpkt.Payload
 	} else {
-		if len(d.fragments) == 0 {
+		if d.fragmentsSize == 0 {
 			if !d.firstPacketReceived {
 				return nil, ErrNonStartingPacketAndNoPrevious
 			}
@@ -80,7 +85,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 		d.fragmentsSize += len(vpkt.Payload)
 
 		if d.fragmentsSize > vp8.MaxFrameSize {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 			return nil, fmt.Errorf("frame size (%d) is too big, maximum is %d", d.fragmentsSize, vp8.MaxFrameSize)
 		}
 
@@ -91,7 +96,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 		}
 
 		frame = joinFragments(d.fragments, d.fragmentsSize)
-		d.fragments = d.fragments[:0]
+		d.resetFragments()
 	}
 
 	return frame, nil

pkg/format/rtpvp9/decoder.go

@@ -41,19 +41,24 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 // Decode decodes a VP9 frame from a RTP packet.
 func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 	var vpkt codecs.VP9Packet
 	_, err := vpkt.Unmarshal(pkt.Payload)
 	if err != nil {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		return nil, err
 	}
 
 	var frame []byte
 
 	if vpkt.B {
-		d.fragments = d.fragments[:0] // discard pending fragments
+		d.resetFragments()
 		d.firstPacketReceived = true
 
 		if !vpkt.E {
@@ -64,7 +69,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 
 		frame = vpkt.Payload
 	} else {
-		if len(d.fragments) == 0 {
+		if d.fragmentsSize == 0 {
 			if !d.firstPacketReceived {
 				return nil, ErrNonStartingPacketAndNoPrevious
 			}
@@ -75,7 +80,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 		d.fragmentsSize += len(vpkt.Payload)
 
 		if d.fragmentsSize > vp9.MaxFrameSize {
-			d.fragments = d.fragments[:0] // discard pending fragments
+			d.resetFragments()
 			return nil, fmt.Errorf("frame size (%d) is too big, maximum is %d", d.fragmentsSize, vp9.MaxFrameSize)
 		}
 
@@ -86,7 +91,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
 		}
 
 		frame = joinFragments(d.fragments, d.fragmentsSize)
-		d.fragments = d.fragments[:0]
+		d.resetFragments()
 	}
 
 	return frame, nil