snapshot of https://github.com/livekit/livekit.git @ 08c5433449c106943231037d0b892895f6e92d3b (2026-09-15)

pkg/sfu/rtpextension/abscapturetime/abscapturetime.go

@@ -0,0 +1,114 @@
+// Copyright 2024 LiveKit, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package abscapturetime
+
+import (
+	"encoding/binary"
+	"errors"
+	"time"
+
+	"github.com/livekit/mediatransportutil"
+)
+
+const (
+	AbsCaptureTimeURI = "http://www.webrtc.org/experiments/rtp-hdrext/abs-capture-time"
+)
+
+var (
+	errInvalidData = errors.New("invalid data")
+	errTooSmall    = errors.New("buffer too small")
+)
+
+// Reference: https://webrtc.googlesource.com/src/+/refs/heads/main/docs/native-code/rtp-hdrext/abs-capture-time/
+//
+// Data layout of the shortened version of abs-capture-time with a 1-byte header + 8 bytes of data:
+//
+//  0                   1                   2                   3
+//  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// |  ID   | len=7 |     absolute capture timestamp (bit 0-23)     |
+// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// |             absolute capture timestamp (bit 24-55)            |
+// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// |  ... (56-63)  |
+// +-+-+-+-+-+-+-+-+
+//
+//Data layout of the extended version of abs-capture-time with a 1-byte header + 16 bytes of data:
+//
+//  0                   1                   2                   3
+//  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// |  ID   | len=15|     absolute capture timestamp (bit 0-23)     |
+// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// |             absolute capture timestamp (bit 24-55)            |
+// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// |  ... (56-63)  |   estimated capture clock offset (bit 0-23)   |
+// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// |           estimated capture clock offset (bit 24-55)          |
+// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// |  ... (56-63)  |
+// +-+-+-+-+-+-+-+-+
+
+type AbsCaptureTime struct {
+	absoluteCaptureTimestamp    mediatransportutil.NtpTime
+	estimatedCaptureClockOffset int64
+}
+
+func AbsCaptureTimeFromValue(absoluteCaptureTimestamp uint64, estimatedCaptureClockOffset int64) *AbsCaptureTime {
+	return &AbsCaptureTime{
+		absoluteCaptureTimestamp:    mediatransportutil.NtpTime(absoluteCaptureTimestamp),
+		estimatedCaptureClockOffset: estimatedCaptureClockOffset,
+	}
+}
+
+func (a *AbsCaptureTime) Rewrite(offset time.Duration) error {
+	if a.absoluteCaptureTimestamp == 0 {
+		return errInvalidData
+	}
+
+	capturedAt := a.absoluteCaptureTimestamp.Time().Add(offset)
+	a.absoluteCaptureTimestamp = mediatransportutil.ToNtpTime(capturedAt)
+	a.estimatedCaptureClockOffset = 0
+	return nil
+}
+
+func (a *AbsCaptureTime) Marshal() ([]byte, error) {
+	if a.absoluteCaptureTimestamp == 0 {
+		return nil, errInvalidData
+	}
+
+	size := 8
+	if a.estimatedCaptureClockOffset != 0 {
+		size += 8
+	}
+	marshalled := make([]byte, size)
+	binary.BigEndian.PutUint64(marshalled, uint64(a.absoluteCaptureTimestamp))
+	if a.estimatedCaptureClockOffset != 0 {
+		binary.BigEndian.PutUint64(marshalled[8:], uint64(a.estimatedCaptureClockOffset))
+	}
+	return marshalled, nil
+}
+
+func (a *AbsCaptureTime) Unmarshal(marshalled []byte) error {
+	if len(marshalled) < 8 {
+		return errTooSmall
+	}
+
+	a.absoluteCaptureTimestamp = mediatransportutil.NtpTime(binary.BigEndian.Uint64(marshalled))
+	if len(marshalled) >= 16 {
+		a.estimatedCaptureClockOffset = int64(binary.BigEndian.Uint64(marshalled[8:]))
+	}
+	return nil
+}