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Support for abs-send-time - closes #1081 #1084

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merged 9 commits into from Mar 21, 2024
Merged

Support for abs-send-time - closes #1081 #1084

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b871b65
Add abs-send-time to each RTP packet
theimowski Mar 4, 2024
b202de3
Add a=rtcp-fb with goog-remb to SDP
theimowski Mar 11, 2024
aae14c3
Move Header Extensions declaration to SDPMediaAnnouncement constructor
theimowski Mar 11, 2024
317a98e
UnixEpoch not available on lower frameworks
theimowski Mar 11, 2024
d74894a
Move AbsSendTime to RTPHeader class
theimowski Mar 11, 2024
f4056e0
Comments for AbsSendTime
theimowski Mar 11, 2024
dc0108e
Send abs-send-time only if remote track supports it
theimowski Mar 11, 2024
c6b9c23
Add unit test
theimowski Mar 11, 2024
2a38481
Revert whitespace changes
theimowski Mar 11, 2024
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6 changes: 6 additions & 0 deletions src/net/RTP/MediaStream.cs
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Expand Up @@ -366,6 +366,12 @@ protected void SendRtpRaw(byte[] data, uint timestamp, int markerBit, int payloa
rtpPacket.Header.MarkerBit = markerBit;
rtpPacket.Header.PayloadType = payloadType;

if (RemoteTrack.HeaderExtensions.TryGetValue(SDPMediaAnnouncement.RTP_HEADER_EXTENSION_ID_ABS_SEND_TIME, out var ext) &&
ext.Uri == SDPMediaAnnouncement.RTP_HEADER_EXTENSION_URI_ABS_SEND_TIME)
{
rtpPacket.Header.AddAbsSendTimeExtension();
}

Buffer.BlockCopy(data, 0, rtpPacket.Payload, 0, data.Length);

var rtpBuffer = rtpPacket.GetBytes();
Expand Down
54 changes: 53 additions & 1 deletion src/net/RTP/RTPHeader.cs
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Expand Up @@ -28,6 +28,7 @@ public class RTPHeader
public const int MIN_HEADER_LEN = 12;

public const int RTP_VERSION = 2;
private const int ONE_BYTE_EXTENSION_PROFILE = 0xBEDE;

public int Version = RTP_VERSION; // 2 bits.
public int PaddingFlag = 0; // 1 bit.
Expand Down Expand Up @@ -253,7 +254,7 @@ public List<RTPHeaderExtensionData> GetHeaderExtensions()

private bool HasOneByteExtension()
{
return ExtensionProfile == 0xBEDE;
return ExtensionProfile == ONE_BYTE_EXTENSION_PROFILE;
}

private bool HasTwoByteExtension()
Expand Down Expand Up @@ -323,5 +324,56 @@ private bool HasTwoByteExtension()
consumed = offset;
return header.PayloadSize>=0;
}

// DateTimeOffset.UnixEpoch only available in newer target frameworks
private static readonly DateTimeOffset UnixEpoch = new DateTimeOffset(1970, 1, 1, 0, 0, 0, TimeSpan.Zero);

// inspired by https://github.com/pion/rtp/blob/master/abssendtimeextension.go
internal static byte[] AbsSendTime(DateTimeOffset now)
{
ulong unixNanoseconds = (ulong)((now - UnixEpoch).Ticks * 100L);
var seconds = unixNanoseconds / (ulong)1e9;
seconds += 0x83AA7E80UL; // offset in seconds between unix epoch and ntp epoch
var f = unixNanoseconds % (ulong)1e9;
f <<= 32;
f /= (ulong)1e9;
seconds <<= 32;
var ntp = seconds | f;
var abs = ntp >> 14;
var length = 2; // extension length (3-1)

return new[]
{
(byte)((SDPMediaAnnouncement.RTP_HEADER_EXTENSION_ID_ABS_SEND_TIME << 4) | length),
(byte)((abs & 0xff0000UL) >> 16),
(byte)((abs & 0xff00UL) >> 8),
(byte)(abs & 0xffUL)
};
}

/*
An example header extension, with three extension elements, some
padding, and including the required RTP fields, follows:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0xBE | 0xDE | length=3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID | L=0 | data | ID | L=1 | data... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...data | 0 (pad) | 0 (pad) | ID | L=3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
// https://datatracker.ietf.org/doc/html/rfc5285#section-4.2
public void AddAbsSendTimeExtension()
{
HeaderExtensionFlag = 1;
ExtensionProfile = ONE_BYTE_EXTENSION_PROFILE;
ExtensionLength = 1; // only abs-send-time for now
ExtensionPayload = AbsSendTime(DateTimeOffset.Now);
}
}
}
6 changes: 3 additions & 3 deletions src/net/SDP/SDP.cs
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Expand Up @@ -434,13 +434,13 @@ public static SDP ParseSDPDescription(string sdpDescription)
}

break;
case var l when l.StartsWith(SDPMediaAnnouncement.MEDIA_FORMAT_ATTRIBUE_PREFIX):
case var l when l.StartsWith(SDPMediaAnnouncement.MEDIA_FORMAT_ATTRIBUTE_PREFIX):
if (activeAnnouncement != null)
{
if (activeAnnouncement.Media == SDPMediaTypesEnum.audio || activeAnnouncement.Media == SDPMediaTypesEnum.video)
{
// Parse the rtpmap attribute for audio/video announcements.
Match formatAttributeMatch = Regex.Match(sdpLineTrimmed, SDPMediaAnnouncement.MEDIA_FORMAT_ATTRIBUE_PREFIX + @"(?<id>\d+)\s+(?<attribute>.*)$");
Match formatAttributeMatch = Regex.Match(sdpLineTrimmed, SDPMediaAnnouncement.MEDIA_FORMAT_ATTRIBUTE_PREFIX + @"(?<id>\d+)\s+(?<attribute>.*)$");
if (formatAttributeMatch.Success)
{
string formatID = formatAttributeMatch.Result("${id}");
Expand Down Expand Up @@ -471,7 +471,7 @@ public static SDP ParseSDPDescription(string sdpDescription)
else
{
// Parse the rtpmap attribute for NON audio/video announcements.
Match formatAttributeMatch = Regex.Match(sdpLineTrimmed, SDPMediaAnnouncement.MEDIA_FORMAT_ATTRIBUE_PREFIX + @"(?<id>\S+)\s+(?<attribute>.*)$");
Match formatAttributeMatch = Regex.Match(sdpLineTrimmed, SDPMediaAnnouncement.MEDIA_FORMAT_ATTRIBUTE_PREFIX + @"(?<id>\S+)\s+(?<attribute>.*)$");
if (formatAttributeMatch.Success)
{
string formatID = formatAttributeMatch.Result("${id}");
Expand Down
8 changes: 8 additions & 0 deletions src/net/SDP/SDPAudioVideoMediaFormat.cs
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Expand Up @@ -96,6 +96,14 @@ public struct SDPAudioVideoMediaFormat
/// </summary>
public string Fmtp { get; }

public IEnumerable<string> SupportedRtcpFeedbackMessages
{
get
{
yield return "goog-remb";
}
}

/// <summary>
/// The standard name of the media format.
/// <code>
Expand Down
27 changes: 23 additions & 4 deletions src/net/SDP/SDPMediaAnnouncement.cs
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Expand Up @@ -70,7 +70,8 @@ public SDPSsrcAttribute(uint ssrc, string cname, string groupID)
public class SDPMediaAnnouncement
{
public const string MEDIA_EXTENSION_MAP_ATTRIBUE_PREFIX = "a=extmap:";
public const string MEDIA_FORMAT_ATTRIBUE_PREFIX = "a=rtpmap:";
public const string MEDIA_FORMAT_ATTRIBUTE_PREFIX = "a=rtpmap:";
public const string MEDIA_FORMAT_FEEDBACK_PREFIX = "a=rtcp-fb:";
public const string MEDIA_FORMAT_PARAMETERS_ATTRIBUE_PREFIX = "a=fmtp:";
public const string MEDIA_FORMAT_SSRC_ATTRIBUE_PREFIX = "a=ssrc:";
public const string MEDIA_FORMAT_SSRC_GROUP_ATTRIBUE_PREFIX = "a=ssrc-group:";
Expand All @@ -80,6 +81,9 @@ public class SDPMediaAnnouncement
public const string MEDIA_FORMAT_PATH_MSRP_PREFIX = "a=path:msrp:";
public const string MEDIA_FORMAT_PATH_ACCEPT_TYPES_PREFIX = "a=accept-types:";
public const string TIAS_BANDWIDTH_ATTRIBUE_PREFIX = "b=TIAS:";
public const int RTP_HEADER_EXTENSION_ID_ABS_SEND_TIME = 2;
public const string RTP_HEADER_EXTENSION_URI_ABS_SEND_TIME = "http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time";

public const MediaStreamStatusEnum DEFAULT_STREAM_STATUS = MediaStreamStatusEnum.SendRecv;

public const string m_CRLF = "\r\n";
Expand Down Expand Up @@ -206,6 +210,16 @@ public SDPMediaAnnouncement(SDPMediaTypesEnum mediaType, int port, List<SDPAudio
}
}
}

HeaderExtensions = new Dictionary<int, RTPHeaderExtension>
{
{
RTP_HEADER_EXTENSION_ID_ABS_SEND_TIME,
new RTPHeaderExtension(
RTP_HEADER_EXTENSION_ID_ABS_SEND_TIME,
RTP_HEADER_EXTENSION_URI_ABS_SEND_TIME)
}
};
}

public SDPMediaAnnouncement(SDPMediaTypesEnum mediaType, int port, List<SDPApplicationMediaFormat> appMediaFormats)
Expand Down Expand Up @@ -422,7 +436,7 @@ public string GetFormatListAttributesToString()
{
if (appFormat.Value.Rtpmap != null)
{
sb.Append($"{MEDIA_FORMAT_ATTRIBUE_PREFIX}{appFormat.Key} {appFormat.Value.Rtpmap}{m_CRLF}");
sb.Append($"{MEDIA_FORMAT_ATTRIBUTE_PREFIX}{appFormat.Key} {appFormat.Value.Rtpmap}{m_CRLF}");
}

if (appFormat.Value.Fmtp != null)
Expand Down Expand Up @@ -474,11 +488,16 @@ public string GetFormatListAttributesToString()
{
// Well known media formats are not required to add an rtpmap but we do so any way as some SIP
// stacks don't work without it.
formatAttributes += MEDIA_FORMAT_ATTRIBUE_PREFIX + mediaFormat.ID + " " + mediaFormat.Name() + "/" + mediaFormat.ClockRate() + m_CRLF;
formatAttributes += MEDIA_FORMAT_ATTRIBUTE_PREFIX + mediaFormat.ID + " " + mediaFormat.Name() + "/" + mediaFormat.ClockRate() + m_CRLF;
}
else
{
formatAttributes += MEDIA_FORMAT_ATTRIBUE_PREFIX + mediaFormat.ID + " " + mediaFormat.Rtpmap + m_CRLF;
formatAttributes += MEDIA_FORMAT_ATTRIBUTE_PREFIX + mediaFormat.ID + " " + mediaFormat.Rtpmap + m_CRLF;
}

foreach (var rtcpFeedbackMessage in mediaFormat.SupportedRtcpFeedbackMessages)
{
formatAttributes += MEDIA_FORMAT_FEEDBACK_PREFIX + mediaFormat.ID + " " + rtcpFeedbackMessage + m_CRLF;
}

if (mediaFormat.Fmtp != null)
Expand Down
15 changes: 15 additions & 0 deletions test/unit/net/RTP/RTPHeaderExtensionUnitTest.cs
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Expand Up @@ -67,5 +67,20 @@ public void ReturnsNullTimestamps()

Assert.Null(timestamps);
}

[Fact]
public void AbsSendTime()
{
logger.LogDebug("--> " + System.Reflection.MethodBase.GetCurrentMethod().Name);
logger.BeginScope(System.Reflection.MethodBase.GetCurrentMethod().Name);

var time = new DateTimeOffset(2024, 2, 11, 14, 51, 02, 999, new TimeSpan(-5, 0, 0));
var bytes = RTPHeader.AbsSendTime(time);

Assert.Equal(0x22, bytes[0]); // 2 for ID and 2 for Length (3-1)
Assert.Equal(155, bytes[1]);
Assert.Equal(254, bytes[2]);
Assert.Equal(249, bytes[3]);
}
}
}