Implement av1 depacketizer

Adds AV1Depacketizer which implements the Depacketizer interface for AV1

Author: JoTurk

codecs/av1_depacketizer.go

@@ -0,0 +1,166 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package codecs
+
+import (
+	"fmt"
+
+	"github.com/pion/rtp/codecs/av1/obu"
+)
+
+const (
+	av1OBUTemporalDelimiter = 2
+	av1OBUTileList          = 8
+)
+
+// AV1Depacketizer is a AV1 RTP Packet depacketizer.
+type AV1Depacketizer struct {
+	// holds the fragmented OBU from the previous packet.
+	buffer []byte
+}
+
+// Unmarshal parses an AV1 RTP payload into its constituent OBU elements.
+// 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
+// it is completed.
+//
+//nolint:gocognit,cyclop
+func (d *AV1Depacketizer) Unmarshal(payload []byte) (buff []byte, err error) {
+	if len(payload) <= 1 {
+		return nil, errShortPacket
+	}
+
+	// |Z|Y| W |N|-|-|-|
+	obuZ := (0b10000000 & payload[0]) != 0     // Z
+	obuY := (0b01000000 & payload[0]) != 0     // Y
+	obuCount := (0b00110000 & payload[0]) >> 4 // W
+	buff = make([]byte, 0)
+
+	// Make sure we clear the buffer if Z is not 0.
+	if !obuZ && len(d.buffer) > 0 {
+		buff = nil
+	}
+
+	obuOffset := 0
+	for offset := 1; offset < len(payload); obuOffset++ {
+		isFirst := obuOffset == 0
+		isLast := obuCount != 0 && obuOffset == int(obuCount)-1
+
+		// https://aomediacodec.github.io/av1-rtp-spec/#44-av1-aggregation-header
+		// W: two bit field that describes the number of OBU elements in the packet.
+		// This field MUST be set equal to 0 or equal to the number of OBU elements contained in the packet.
+		// If set to 0, each OBU element MUST be preceded by a length field. If not set to 0
+		// (i.e., W = 1, 2 or 3) the last OBU element MUST NOT be preceded by a length field.
+		var obuSize, n int
+		if obuCount == 0 || !isLast {
+			obuSizeVal, nVal, err := obu.ReadLeb128(payload[offset:])
+			obuSize = int(obuSizeVal) //nolint:gosec // G115 false positive
+			n = int(nVal)             //nolint:gosec // G115 false positive
+			if err != nil {
+				return nil, err
+			}
+
+			offset += n
+			if obuCount == 0 && offset+obuSize == len(payload) {
+				isLast = true
+			}
+		} else {
+			// https://aomediacodec.github.io/av1-rtp-spec/#44-av1-aggregation-header
+			// Length of the last OBU element =
+			// length of the RTP payload
+			// - length of aggregation header
+			// - length of previous OBU elements including length fields
+			obuSize = len(payload) - offset
+		}
+
+		if offset+obuSize > len(payload) {
+			return nil, fmt.Errorf(
+				"%w: OBU size %d + %d offset exceeds payload length %d",
+				errShortPacket, obuSize, offset, len(payload),
+			)
+		}
+
+		var obuBuffer []byte
+		if isFirst && obuZ {
+			// We lost the first fragment of the OBU
+			// We drop the buffer and continue
+			if len(d.buffer) == 0 {
+				if isLast {
+					break
+				}
+
+				offset += obuSize
+
+				continue
+			}
+
+			obuBuffer = make([]byte, len(d.buffer)+obuSize)
+
+			copy(obuBuffer, d.buffer)
+			copy(obuBuffer[len(d.buffer):], payload[offset:offset+obuSize])
+			d.buffer = nil
+		} else {
+			obuBuffer = payload[offset : offset+obuSize]
+		}
+		offset += obuSize
+
+		if isLast && obuY {
+			d.buffer = obuBuffer
+		} else {
+			if len(obuBuffer) == 0 {
+				return nil, fmt.Errorf(
+					"%w: OBU size %d is 0",
+					errShortPacket, obuSize,
+				)
+			}
+
+			// The temporal delimiter OBU, if present, SHOULD be removed when transmitting,
+			// and MUST be ignored by receivers. Tile list OBUs are not supported.
+			// They SHOULD be removed when transmitted, and MUST be ignored by receivers.
+			// https://aomediacodec.github.io/av1-rtp-spec/#5-packetization-rules
+
+			obuType := (obuBuffer[0] & obuFrameTypeMask) >> obuFrameTypeBitshift
+
+			if obuType != av1OBUTemporalDelimiter && obuType != av1OBUTileList {
+				buff = append(buff, obuBuffer...)
+			}
+		}
+
+		if isLast {
+			break
+		}
+	}
+
+	if obuCount != 0 && obuOffset != int(obuCount-1) {
+		return nil, fmt.Errorf(
+			"%w: OBU count %d does not match number of OBUs %d",
+			errShortPacket, obuCount, obuOffset,
+		)
+	}
+
+	return buff, nil
+}
+
+// IsPartitionTail returns true if RTP packet marker is set.
+// Clear the buffer if we are at the end of the partition.
+func (d *AV1Depacketizer) IsPartitionTail(marker bool, _ []byte) bool {
+	if marker {
+		// We make sure we clear the buffer if we are at the end of the partition.
+		d.buffer = nil
+
+		return true
+	}
+
+	return false
+}
+
+// IsPartitionHead returns true if Z in the AV1 Aggregation Header
+// is set to 0.
+func (d *AV1Depacketizer) IsPartitionHead(payload []byte) bool {
+	if len(payload) == 0 {
+		return false
+	}
+
+	return (payload[0] & 0b11000000) == 0
+}