modules/rtp_rtcp/source/rtp_header_extensions.cc

/*
 *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "modules/rtp_rtcp/source/rtp_header_extensions.h"

#include <string.h>
#include <cmath>

#include "modules/rtp_rtcp/include/rtp_cvo.h"
#include "modules/rtp_rtcp/source/byte_io.h"
// TODO(bug:9855) Move kNoSpatialIdx from vp9_globals.h to common_constants
#include "modules/video_coding/codecs/interface/common_constants.h"
#include "rtc_base/checks.h"

namespace webrtc {
// Absolute send time in RTP streams.
//
// The absolute send time is signaled to the receiver in-band using the
// general mechanism for RTP header extensions [RFC8285]. The payload
// of this extension (the transmitted value) is a 24-bit unsigned integer
// containing the sender's current time in seconds as a fixed point number
// with 18 bits fractional part.
//
// The form of the absolute send time extension block:
//
//    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=2 |              absolute send time               |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
constexpr RTPExtensionType AbsoluteSendTime::kId;
constexpr uint8_t AbsoluteSendTime::kValueSizeBytes;
constexpr const char AbsoluteSendTime::kUri[];

bool AbsoluteSendTime::Parse(rtc::ArrayView<const uint8_t> data,
                             uint32_t* time_24bits) {
  if (data.size() != 3)
    return false;
  *time_24bits = ByteReader<uint32_t, 3>::ReadBigEndian(data.data());
  return true;
}

bool AbsoluteSendTime::Write(rtc::ArrayView<uint8_t> data,
                             uint32_t time_24bits) {
  RTC_DCHECK_EQ(data.size(), 3);
  RTC_DCHECK_LE(time_24bits, 0x00FFFFFF);
  ByteWriter<uint32_t, 3>::WriteBigEndian(data.data(), time_24bits);
  return true;
}

// An RTP Header Extension for Client-to-Mixer Audio Level Indication
//
// https://datatracker.ietf.org/doc/draft-lennox-avt-rtp-audio-level-exthdr/
//
// The form of the audio level extension block:
//
//    0                   1
//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |  ID   | len=0 |V|   level     |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//
constexpr RTPExtensionType AudioLevel::kId;
constexpr uint8_t AudioLevel::kValueSizeBytes;
constexpr const char AudioLevel::kUri[];

bool AudioLevel::Parse(rtc::ArrayView<const uint8_t> data,
                       bool* voice_activity,
                       uint8_t* audio_level) {
  if (data.size() != 1)
    return false;
  *voice_activity = (data[0] & 0x80) != 0;
  *audio_level = data[0] & 0x7F;
  return true;
}

bool AudioLevel::Write(rtc::ArrayView<uint8_t> data,
                       bool voice_activity,
                       uint8_t audio_level) {
  RTC_DCHECK_EQ(data.size(), 1);
  RTC_CHECK_LE(audio_level, 0x7f);
  data[0] = (voice_activity ? 0x80 : 0x00) | audio_level;
  return true;
}

// From RFC 5450: Transmission Time Offsets in RTP Streams.
//
// The transmission time is signaled to the receiver in-band using the
// general mechanism for RTP header extensions [RFC8285]. The payload
// of this extension (the transmitted value) is a 24-bit signed integer.
// When added to the RTP timestamp of the packet, it represents the
// "effective" RTP transmission time of the packet, on the RTP
// timescale.
//
// The form of the transmission offset extension block:
//
//    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=2 |              transmission offset              |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
constexpr RTPExtensionType TransmissionOffset::kId;
constexpr uint8_t TransmissionOffset::kValueSizeBytes;
constexpr const char TransmissionOffset::kUri[];

bool TransmissionOffset::Parse(rtc::ArrayView<const uint8_t> data,
                               int32_t* rtp_time) {
  if (data.size() != 3)
    return false;
  *rtp_time = ByteReader<int32_t, 3>::ReadBigEndian(data.data());
  return true;
}

bool TransmissionOffset::Write(rtc::ArrayView<uint8_t> data, int32_t rtp_time) {
  RTC_DCHECK_EQ(data.size(), 3);
  RTC_DCHECK_LE(rtp_time, 0x00ffffff);
  ByteWriter<int32_t, 3>::WriteBigEndian(data.data(), rtp_time);
  return true;
}

//   0                   1                   2
//   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//  |  ID   | L=1   |transport wide sequence number |
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
constexpr RTPExtensionType TransportSequenceNumber::kId;
constexpr uint8_t TransportSequenceNumber::kValueSizeBytes;
constexpr const char TransportSequenceNumber::kUri[];

bool TransportSequenceNumber::Parse(rtc::ArrayView<const uint8_t> data,
                                    uint16_t* value) {
  if (data.size() != 2)
    return false;
  *value = ByteReader<uint16_t>::ReadBigEndian(data.data());
  return true;
}

bool TransportSequenceNumber::Write(rtc::ArrayView<uint8_t> data,
                                    uint16_t value) {
  RTC_DCHECK_EQ(data.size(), 2);
  ByteWriter<uint16_t>::WriteBigEndian(data.data(), value);
  return true;
}

// Coordination of Video Orientation in RTP streams.
//
// Coordination of Video Orientation consists in signaling of the current
// orientation of the image captured on the sender side to the receiver for
// appropriate rendering and displaying.
//
//    0                   1
//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |  ID   | len=0 |0 0 0 0 C F R R|
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
constexpr RTPExtensionType VideoOrientation::kId;
constexpr uint8_t VideoOrientation::kValueSizeBytes;
constexpr const char VideoOrientation::kUri[];

bool VideoOrientation::Parse(rtc::ArrayView<const uint8_t> data,
                             VideoRotation* rotation) {
  if (data.size() != 1)
    return false;
  *rotation = ConvertCVOByteToVideoRotation(data[0]);
  return true;
}

bool VideoOrientation::Write(rtc::ArrayView<uint8_t> data,
                             VideoRotation rotation) {
  RTC_DCHECK_EQ(data.size(), 1);
  data[0] = ConvertVideoRotationToCVOByte(rotation);
  return true;
}

bool VideoOrientation::Parse(rtc::ArrayView<const uint8_t> data,
                             uint8_t* value) {
  if (data.size() != 1)
    return false;
  *value = data[0];
  return true;
}

bool VideoOrientation::Write(rtc::ArrayView<uint8_t> data, uint8_t value) {
  RTC_DCHECK_EQ(data.size(), 1);
  data[0] = value;
  return true;
}

//   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=2 |   MIN delay           |   MAX delay           |
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
constexpr RTPExtensionType PlayoutDelayLimits::kId;
constexpr uint8_t PlayoutDelayLimits::kValueSizeBytes;
constexpr const char PlayoutDelayLimits::kUri[];

bool PlayoutDelayLimits::Parse(rtc::ArrayView<const uint8_t> data,
                               PlayoutDelay* playout_delay) {
  RTC_DCHECK(playout_delay);
  if (data.size() != 3)
    return false;
  uint32_t raw = ByteReader<uint32_t, 3>::ReadBigEndian(data.data());
  uint16_t min_raw = (raw >> 12);
  uint16_t max_raw = (raw & 0xfff);
  if (min_raw > max_raw)
    return false;
  playout_delay->min_ms = min_raw * kGranularityMs;
  playout_delay->max_ms = max_raw * kGranularityMs;
  return true;
}

bool PlayoutDelayLimits::Write(rtc::ArrayView<uint8_t> data,
                               const PlayoutDelay& playout_delay) {
  RTC_DCHECK_EQ(data.size(), 3);
  RTC_DCHECK_LE(0, playout_delay.min_ms);
  RTC_DCHECK_LE(playout_delay.min_ms, playout_delay.max_ms);
  RTC_DCHECK_LE(playout_delay.max_ms, kMaxMs);
  // Convert MS to value to be sent on extension header.
  uint32_t min_delay = playout_delay.min_ms / kGranularityMs;
  uint32_t max_delay = playout_delay.max_ms / kGranularityMs;
  ByteWriter<uint32_t, 3>::WriteBigEndian(data.data(),
                                          (min_delay << 12) | max_delay);
  return true;
}

// Video Content Type.
//
// E.g. default video or screenshare.
//
//    0                   1
//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |  ID   | len=0 | Content type  |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
constexpr RTPExtensionType VideoContentTypeExtension::kId;
constexpr uint8_t VideoContentTypeExtension::kValueSizeBytes;
constexpr const char VideoContentTypeExtension::kUri[];

bool VideoContentTypeExtension::Parse(rtc::ArrayView<const uint8_t> data,
                                      VideoContentType* content_type) {
  if (data.size() == 1 &&
      videocontenttypehelpers::IsValidContentType(data[0])) {
    *content_type = static_cast<VideoContentType>(data[0]);
    return true;
  }
  return false;
}

bool VideoContentTypeExtension::Write(rtc::ArrayView<uint8_t> data,
                                      VideoContentType content_type) {
  RTC_DCHECK_EQ(data.size(), 1);
  data[0] = static_cast<uint8_t>(content_type);
  return true;
}

// Video Timing.
// 6 timestamps in milliseconds counted from capture time stored in rtp header:
// encode start/finish, packetization complete, pacer exit and reserved for
// modification by the network modification. |flags| is a bitmask and has the
// following allowed values:
// 0 = Valid data, but no flags available (backwards compatibility)
// 1 = Frame marked as timing frame due to cyclic timer.
// 2 = Frame marked as timing frame due to size being outside limit.
// 255 = Invalid. The whole timing frame extension should be ignored.
//
//    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 2
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |  ID   | len=12|     flags     |     encode start ms delta       |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |    encode finish ms delta     |   packetizer finish ms delta    |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |     pacer exit ms delta       |   network timestamp ms delta    |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |  network2 timestamp ms delta  |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

constexpr RTPExtensionType VideoTimingExtension::kId;
constexpr uint8_t VideoTimingExtension::kValueSizeBytes;
constexpr const char VideoTimingExtension::kUri[];

bool VideoTimingExtension::Parse(rtc::ArrayView<const uint8_t> data,
                                 VideoSendTiming* timing) {
  RTC_DCHECK(timing);
  // TODO(sprang): Deprecate support for old wire format.
  ptrdiff_t off = 0;
  switch (data.size()) {
    case kValueSizeBytes - 1:
      timing->flags = 0;
      off = 1;  // Old wire format without the flags field.
      break;
    case kValueSizeBytes:
      timing->flags = ByteReader<uint8_t>::ReadBigEndian(data.data());
      break;
    default:
      return false;
  }

  timing->encode_start_delta_ms = ByteReader<uint16_t>::ReadBigEndian(
      data.data() + VideoSendTiming::kEncodeStartDeltaOffset - off);
  timing->encode_finish_delta_ms = ByteReader<uint16_t>::ReadBigEndian(
      data.data() + VideoSendTiming::kEncodeFinishDeltaOffset - off);
  timing->packetization_finish_delta_ms = ByteReader<uint16_t>::ReadBigEndian(
      data.data() + VideoSendTiming::kPacketizationFinishDeltaOffset - off);
  timing->pacer_exit_delta_ms = ByteReader<uint16_t>::ReadBigEndian(
      data.data() + VideoSendTiming::kPacerExitDeltaOffset - off);
  timing->network_timestamp_delta_ms = ByteReader<uint16_t>::ReadBigEndian(
      data.data() + VideoSendTiming::kNetworkTimestampDeltaOffset - off);
  timing->network2_timestamp_delta_ms = ByteReader<uint16_t>::ReadBigEndian(
      data.data() + VideoSendTiming::kNetwork2TimestampDeltaOffset - off);
  return true;
}

bool VideoTimingExtension::Write(rtc::ArrayView<uint8_t> data,
                                 const VideoSendTiming& timing) {
  RTC_DCHECK_EQ(data.size(), 1 + 2 * 6);
  ByteWriter<uint8_t>::WriteBigEndian(
      data.data() + VideoSendTiming::kFlagsOffset, timing.flags);
  ByteWriter<uint16_t>::WriteBigEndian(
      data.data() + VideoSendTiming::kEncodeStartDeltaOffset,
      timing.encode_start_delta_ms);
  ByteWriter<uint16_t>::WriteBigEndian(
      data.data() + VideoSendTiming::kEncodeFinishDeltaOffset,
      timing.encode_finish_delta_ms);
  ByteWriter<uint16_t>::WriteBigEndian(
      data.data() + VideoSendTiming::kPacketizationFinishDeltaOffset,
      timing.packetization_finish_delta_ms);
  ByteWriter<uint16_t>::WriteBigEndian(
      data.data() + VideoSendTiming::kPacerExitDeltaOffset,
      timing.pacer_exit_delta_ms);
  ByteWriter<uint16_t>::WriteBigEndian(
      data.data() + VideoSendTiming::kNetworkTimestampDeltaOffset,
      timing.network_timestamp_delta_ms);
  ByteWriter<uint16_t>::WriteBigEndian(
      data.data() + VideoSendTiming::kNetwork2TimestampDeltaOffset,
      timing.network2_timestamp_delta_ms);
  return true;
}

bool VideoTimingExtension::Write(rtc::ArrayView<uint8_t> data,
                                 uint16_t time_delta_ms,
                                 uint8_t offset) {
  RTC_DCHECK_GE(data.size(), offset + 2);
  RTC_DCHECK_LE(offset, kValueSizeBytes - sizeof(uint16_t));
  ByteWriter<uint16_t>::WriteBigEndian(data.data() + offset, time_delta_ms);
  return true;
}

// Frame Marking.
//
// Meta-information about an RTP stream outside the encrypted media payload,
// useful for an RTP switch to do codec-agnostic selective forwarding
// without decrypting the payload.
//
// For non-scalable streams:
//    0                   1
//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |  ID   | L = 0 |S|E|I|D|0 0 0 0|
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//
// For scalable streams:
//    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   | L = 2 |S|E|I|D|B| TID |      LID      |   TL0PICIDX   |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

constexpr RTPExtensionType FrameMarkingExtension::kId;
constexpr const char FrameMarkingExtension::kUri[];

bool FrameMarkingExtension::IsScalable(uint8_t temporal_id, uint8_t layer_id) {
  return temporal_id != kNoTemporalIdx || layer_id != kNoSpatialIdx;
}

bool FrameMarkingExtension::Parse(rtc::ArrayView<const uint8_t> data,
                                  FrameMarking* frame_marking) {
  RTC_DCHECK(frame_marking);

  if (data.size() != 1 && data.size() != 3)
    return false;

  frame_marking->start_of_frame = (data[0] & 0x80) != 0;
  frame_marking->end_of_frame = (data[0] & 0x40) != 0;
  frame_marking->independent_frame = (data[0] & 0x20) != 0;
  frame_marking->discardable_frame = (data[0] & 0x10) != 0;

  if (data.size() == 3) {
    frame_marking->base_layer_sync = (data[0] & 0x08) != 0;
    frame_marking->temporal_id = data[0] & 0x7;
    frame_marking->layer_id = data[1];
    frame_marking->tl0_pic_idx = data[2];
  } else {
    // non-scalable
    frame_marking->base_layer_sync = false;
    frame_marking->temporal_id = kNoTemporalIdx;
    frame_marking->layer_id = kNoSpatialIdx;
    frame_marking->tl0_pic_idx = 0;
  }
  return true;
}

size_t FrameMarkingExtension::ValueSize(const FrameMarking& frame_marking) {
  if (IsScalable(frame_marking.temporal_id, frame_marking.layer_id))
    return 3;
  else
    return 1;
}

bool FrameMarkingExtension::Write(rtc::ArrayView<uint8_t> data,
                                  const FrameMarking& frame_marking) {
  RTC_DCHECK_GE(data.size(), 1);
  RTC_CHECK_LE(frame_marking.temporal_id, 0x07);
  data[0] = frame_marking.start_of_frame ? 0x80 : 0x00;
  data[0] |= frame_marking.end_of_frame ? 0x40 : 0x00;
  data[0] |= frame_marking.independent_frame ? 0x20 : 0x00;
  data[0] |= frame_marking.discardable_frame ? 0x10 : 0x00;

  if (IsScalable(frame_marking.temporal_id, frame_marking.layer_id)) {
    RTC_DCHECK_EQ(data.size(), 3);
    data[0] |= frame_marking.base_layer_sync ? 0x08 : 0x00;
    data[0] |= frame_marking.temporal_id & 0x07;
    data[1] = frame_marking.layer_id;
    data[2] = frame_marking.tl0_pic_idx;
  }
  return true;
}

// HDR Metadata.
//
// RTP header extension to carry HDR metadata.
// Float values are upscaled by a static factor and transmitted as integers.
//
//    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 2
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |       ID      |     length    |                 luminance_max   |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |               |                  luminance_min                  |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |              mastering_metadata.primary_r.x and .y              |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |              mastering_metadata.primary_g.x and .y              |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |              mastering_metadata.primary_b.x and .y              |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |                mastering_metadata.white.x and .y                |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |                     max_content_light_level                     |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |                  max_frame_average_light_level                  |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
constexpr RTPExtensionType HdrMetadataExtension::kId;
constexpr uint8_t HdrMetadataExtension::kValueSizeBytes;
constexpr const char HdrMetadataExtension::kUri[];

bool HdrMetadataExtension::Parse(rtc::ArrayView<const uint8_t> data,
                                 HdrMetadata* hdr_metadata) {
  RTC_DCHECK(hdr_metadata);
  if (data.size() != kValueSizeBytes)
    return false;

  size_t offset = 0;
  offset += ParseLuminance(data.data() + offset,
                           &hdr_metadata->mastering_metadata.luminance_max,
                           kLuminanceMaxDenominator);
  offset += ParseLuminance(data.data() + offset,
                           &hdr_metadata->mastering_metadata.luminance_min,
                           kLuminanceMinDenominator);
  offset += ParseChromaticity(data.data() + offset,
                              &hdr_metadata->mastering_metadata.primary_r);
  offset += ParseChromaticity(data.data() + offset,
                              &hdr_metadata->mastering_metadata.primary_g);
  offset += ParseChromaticity(data.data() + offset,
                              &hdr_metadata->mastering_metadata.primary_b);
  offset += ParseChromaticity(data.data() + offset,
                              &hdr_metadata->mastering_metadata.white_point);
  // TODO(kron): Do we need 32 bit here or is it enough with 16 bits?
  // Also, what resolution is needed?
  hdr_metadata->max_content_light_level =
      ByteReader<uint32_t>::ReadBigEndian(data.data() + offset);
  offset += 4;
  hdr_metadata->max_frame_average_light_level =
      ByteReader<uint32_t>::ReadBigEndian(data.data() + offset);
  RTC_DCHECK_EQ(kValueSizeBytes, offset + 4);
  return true;
}

bool HdrMetadataExtension::Write(rtc::ArrayView<uint8_t> data,
                                 const HdrMetadata& hdr_metadata) {
  RTC_DCHECK_EQ(data.size(), kValueSizeBytes);
  size_t offset = 0;
  offset += WriteLuminance(data.data() + offset,
                           hdr_metadata.mastering_metadata.luminance_max,
                           kLuminanceMaxDenominator);
  offset += WriteLuminance(data.data() + offset,
                           hdr_metadata.mastering_metadata.luminance_min,
                           kLuminanceMinDenominator);
  offset += WriteChromaticity(data.data() + offset,
                              hdr_metadata.mastering_metadata.primary_r);
  offset += WriteChromaticity(data.data() + offset,
                              hdr_metadata.mastering_metadata.primary_g);
  offset += WriteChromaticity(data.data() + offset,
                              hdr_metadata.mastering_metadata.primary_b);
  offset += WriteChromaticity(data.data() + offset,
                              hdr_metadata.mastering_metadata.white_point);

  // TODO(kron): Do we need 32 bit here or is it enough with 16 bits?
  // Also, what resolution is needed?
  ByteWriter<uint32_t>::WriteBigEndian(data.data() + offset,
                                       hdr_metadata.max_content_light_level);
  offset += 4;
  ByteWriter<uint32_t>::WriteBigEndian(
      data.data() + offset, hdr_metadata.max_frame_average_light_level);
  RTC_DCHECK_EQ(kValueSizeBytes, offset + 4);
  return true;
}

size_t HdrMetadataExtension::ParseChromaticity(
    const uint8_t* data,
    HdrMasteringMetadata::Chromaticity* p) {
  uint16_t chromaticity_x_scaled = ByteReader<uint16_t>::ReadBigEndian(data);
  uint16_t chromaticity_y_scaled =
      ByteReader<uint16_t>::ReadBigEndian(data + 2);
  p->x = static_cast<float>(chromaticity_x_scaled) / kChromaticityDenominator;
  p->y = static_cast<float>(chromaticity_y_scaled) / kChromaticityDenominator;
  return 4;  // Return number of bytes read.
}

size_t HdrMetadataExtension::ParseLuminance(const uint8_t* data,
                                            float* f,
                                            int denominator) {
  uint32_t luminance_scaled = ByteReader<uint32_t, 3>::ReadBigEndian(data);
  *f = static_cast<float>(luminance_scaled) / denominator;
  return 3;  // Return number of bytes read.
}

size_t HdrMetadataExtension::WriteChromaticity(
    uint8_t* data,
    const HdrMasteringMetadata::Chromaticity& p) {
  RTC_DCHECK_GE(p.x, 0.0f);
  RTC_DCHECK_GE(p.y, 0.0f);
  ByteWriter<uint16_t>::WriteBigEndian(
      data, std::round(p.x * kChromaticityDenominator));
  ByteWriter<uint16_t>::WriteBigEndian(
      data + 2, std::round(p.y * kChromaticityDenominator));
  return 4;  // Return number of bytes written.
}

size_t HdrMetadataExtension::WriteLuminance(uint8_t* data,
                                            float f,
                                            int denominator) {
  RTC_DCHECK_GE(f, 0.0f);
  ByteWriter<uint32_t, 3>::WriteBigEndian(data, std::round(f * denominator));
  return 3;  // Return number of bytes written.
}

bool BaseRtpStringExtension::Parse(rtc::ArrayView<const uint8_t> data,
                                   StringRtpHeaderExtension* str) {
  if (data.empty() || data[0] == 0)  // Valid string extension can't be empty.
    return false;
  str->Set(data);
  RTC_DCHECK(!str->empty());
  return true;
}

bool BaseRtpStringExtension::Write(rtc::ArrayView<uint8_t> data,
                                   const StringRtpHeaderExtension& str) {
  RTC_DCHECK_EQ(data.size(), str.size());
  RTC_DCHECK_GE(str.size(), 1);
  RTC_DCHECK_LE(str.size(), StringRtpHeaderExtension::kMaxSize);
  memcpy(data.data(), str.data(), str.size());
  return true;
}

bool BaseRtpStringExtension::Parse(rtc::ArrayView<const uint8_t> data,
                                   std::string* str) {
  if (data.empty() || data[0] == 0)  // Valid string extension can't be empty.
    return false;
  const char* cstr = reinterpret_cast<const char*>(data.data());
  // If there is a \0 character in the middle of the |data|, treat it as end
  // of the string. Well-formed string extensions shouldn't contain it.
  str->assign(cstr, strnlen(cstr, data.size()));
  RTC_DCHECK(!str->empty());
  return true;
}

bool BaseRtpStringExtension::Write(rtc::ArrayView<uint8_t> data,
                                   const std::string& str) {
  if (str.size() > StringRtpHeaderExtension::kMaxSize) {
    return false;
  }
  RTC_DCHECK_EQ(data.size(), str.size());
  RTC_DCHECK_GE(str.size(), 1);
  memcpy(data.data(), str.data(), str.size());
  return true;
}

// Constant declarations for string RTP header extension types.

constexpr RTPExtensionType RtpStreamId::kId;
constexpr const char RtpStreamId::kUri[];

constexpr RTPExtensionType RepairedRtpStreamId::kId;
constexpr const char RepairedRtpStreamId::kUri[];

constexpr RTPExtensionType RtpMid::kId;
constexpr const char RtpMid::kUri[];

}  // namespace webrtc