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Add a Bitrate Controller (#1347)
* fix stream retrieval bug RTC updates * add translations for tray app and installer * fix for ptz serialization use wyze camera name from url * fix bug in g722 codec * Only get stream format once Add timeout to ice gathering Add prefer H264 flag for compatible formats * revert * Optimise SendVideo and SendAudio (only get SendingFormat once) Add sanity check for ICE Gathering timeout * Optimise SendVideo and SendAudio (only get SendingFormat once) Add sanity check for ICE Gathering timeout Fix bug in g722 codec * remove turn folder * Remove turn folder * Move gather timeout to config * Fix rounding bug in SendAudioFrame Fix bug where duplicate durations were being added to local track timestamp in SendAudioFrame Ignore H264 formats that use unsupported packetization modes Clean up logic in AreMatch * remove comment marker * Check for null * Fix bug with HasVideo and HasAudio * Fix locking issue * fix lock * Fix stuttering on connect * Fix DtlsSrtpTransport bug * Fix issues with buffer over-runs * Add TWCC header extension support * Add support for TWCC Fix SDP parsing of audio m fields with ports Return null if stream not matched (was causing issues with RTP processing) Use PrimaryStream to unprotect incoming RTP packets Fix logic bug in SendRtpRaw Prevent some buffer over-reads var videoExtensions = new Dictionary<int, RTPHeaderExtension>(); videoExtensions.Add(extensionId, RTPHeaderExtension.GetRTPHeaderExtension(extensionId++, TransportWideCCExtension.RTP_HEADER_EXTENSION_URI, SDPMediaTypesEnum.video)); MediaStreamTrack videoTrack = new MediaStreamTrack(SDPMediaTypesEnum.video, false, formats.Select(x => new SDPAudioVideoMediaFormat(x)).ToList(), MediaStreamStatusEnum.SendOnly, null, videoExtensions ); in OnReceiveReport access rr.TWCCFeedback * Use feedback type parser * Add notes * Fix limit check * Fix issues with parsing TWCC packet parsing * ignore invalid chunkType * remove console.writeline * Update src/net/RTCP/RTCPCompoundPacket.cs Co-authored-by: Paulo Morgado <[email protected]> * Update src/net/RTCP/RTCPCompoundPacket.cs Co-authored-by: Paulo Morgado <[email protected]> * Update for code review * remove announcement portcount (move to new PR) * Add SRTP fallback * bug fix * add controller class * add comments * move file --------- Co-authored-by: Paulo Morgado <[email protected]>
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‎src/core/TWCCBitrateController.cs

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/*
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* Filename: TWCCBitrateController.cs
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*
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* Description:
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* Uses TWCC Reports to adjust bitrates and framerates for video streams.
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*
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* Author: Sean Tearney
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* Date: 2025 - 03 - 05
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*
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* License: BSD 3-Clause "New" or "Revised" License, see included LICENSE.md file.
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*
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* Change Log:
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* 2025-03-05 Initial creation.
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*/
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using System;
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using SIPSorcery.Net;
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using SIPSorceryMedia.Abstractions;
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namespace SIPSorcery.core
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{
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public class BitrateUpdateEventArgs : EventArgs
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{
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public int Bitrate { get; set; }
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public int Framerate { get; set; }
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public BitrateUpdateEventArgs(double bitrate, double framerate)
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{
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Bitrate = (int)bitrate;
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Framerate = (int)framerate;
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}
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}
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/// <summary>
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/// A controller that uses TWCC feedback reports
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/// to adjust the encoder bitrate based on measured network conditions
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/// over a rolling window using an exponential moving average (EMA).
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/// </summary>
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public class TWCCBitrateController
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{
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public event EventHandler<BitrateUpdateEventArgs> OnBitrateChange;
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private double _currentBitrate; // in bits per second
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private readonly double _minBitrate = 60000;
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private double _maxBitrate;
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// EMA for delay (µs) and loss rate (0 to 1).
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private double _rollingAvgDelay;
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private double _rollingLossRate;
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private bool _isFirstFeedback = true;
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// Smoothing factor for EMA. Smaller alpha => slower reaction.
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private const double Alpha = 0.1;
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// Interval (ms) at which we update the encoder bitrate.
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private const int UpdateIntervalMs = 1000; // 1 second
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private DateTime _lastUpdateTime;
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// For accumulating feedback in the current interval.
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private int _accumReceivedCount;
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private int _accumLostCount;
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private double _accumDelaySum;
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private double _maxFramerate;
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private double _minFramerate = 2;
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private double _framerate;
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private bool _inited = false;
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// Thread-safety lock if needed
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private readonly object _lock = new object();
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public TWCCBitrateController()
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{
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_lastUpdateTime = DateTime.UtcNow;
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}
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/// <summary>
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/// Add a new feedback report. We accumulate the stats,
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/// but only update the actual bitrate on a fixed interval.
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/// </summary>
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public void ProcessFeedback(RTCPTWCCFeedback feedback)
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{
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if (feedback == null || !_inited) { return; }
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lock (_lock)
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{
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foreach (var ps in feedback.PacketStatuses)
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{
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switch (ps.Status)
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{
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case TWCCPacketStatusType.NotReceived:
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_accumLostCount++;
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break;
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case TWCCPacketStatusType.ReceivedSmallDelta:
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case TWCCPacketStatusType.ReceivedLargeDelta:
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if (ps.Delta.HasValue)
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{
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// Add the delay (µs).
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_accumDelaySum += Math.Abs(ps.Delta.Value);
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_accumReceivedCount++;
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}
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break;
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}
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}
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var now = DateTime.UtcNow;
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double elapsedMs = (now - _lastUpdateTime).TotalMilliseconds;
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// Check if it's time to update the bitrate.
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if (elapsedMs >= UpdateIntervalMs)
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{
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// Compute average stats over this interval
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double intervalAvgDelay = 0.0;
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double intervalLossRate = 0.0;
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int totalPackets = _accumReceivedCount + _accumLostCount;
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if (totalPackets > 0)
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{
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intervalAvgDelay = _accumDelaySum / _accumReceivedCount;
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intervalLossRate = (double)_accumLostCount / totalPackets;
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}
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// Reset accumulators for the next interval.
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_accumDelaySum = 0.0;
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_accumReceivedCount = 0;
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_accumLostCount = 0;
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// Update rolling averages (EMA).
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if (_isFirstFeedback)
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{
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_rollingAvgDelay = intervalAvgDelay;
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_rollingLossRate = intervalLossRate;
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_isFirstFeedback = false;
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}
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else
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{
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_rollingAvgDelay = (1 - Alpha) * _rollingAvgDelay + Alpha * intervalAvgDelay;
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_rollingLossRate = (1 - Alpha) * _rollingLossRate + Alpha * intervalLossRate;
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}
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// Adjust the bitrate with a simple AIMD logic.
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// Example thresholds (tune to your environment!):
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const double highDelayThreshold = 100000.0; // 100 ms in microseconds
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const double superHighDelayThreshold = 200000.0; // 200 ms in microseconds
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const double lossThreshold = 0.05; // 5% loss
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const double superHighLossThreshold = 0.15; // 15% loss
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if (_rollingAvgDelay > highDelayThreshold || _rollingLossRate > lossThreshold)
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{
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if (_rollingAvgDelay > superHighDelayThreshold || _rollingLossRate > superHighLossThreshold)
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{
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// Super high delay: more drastic reduction.
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_currentBitrate *= 0.5;
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_framerate *= 0.5;
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}
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else
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{
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// Congestion: decrease bitrate by 15%.
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_currentBitrate *= 0.85;
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_framerate *= 0.85;
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}
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}
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else
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{
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// Good network: increase by 20 kbps.
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_currentBitrate += 20000;
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_framerate *= 1.1;
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}
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// Clamp
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_currentBitrate = Math.Max(_minBitrate, Math.Min(_currentBitrate, _maxBitrate));
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_framerate = Math.Max(_minFramerate, Math.Min(_framerate, _maxFramerate));
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// Update the encoder bitrate
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OnBitrateChange?.Invoke(this, new BitrateUpdateEventArgs(_currentBitrate, _framerate));
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// Log for debugging
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//Debug.WriteLine(
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// $"[TWCCBitrateController] IntervalAvgDelay: {intervalAvgDelay:F1}µs, IntervalLossRate: {intervalLossRate:P1}, " +
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// $"RollingAvgDelay: {_rollingAvgDelay:F1}µs, RollingLossRate: {_rollingLossRate:P1}, MaxBitRate: {_maxBitrate:F0}, NewBitrate: {_currentBitrate:F0}bps");
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_lastUpdateTime = now;
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}
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}
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}
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public void CalculateMaxBitrate(int width, int height, int framerate, VideoCodecsEnum codec)
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{
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// Base bitrates in kbps at 1fps
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int baseBitratePerFrame;
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if (codec == VideoCodecsEnum.H264)
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{
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if (width * height <= 352 * 288)
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{
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// CIF or smaller
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baseBitratePerFrame = 13;
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}
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else if (width * height <= 640 * 480)
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{
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// VGA
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baseBitratePerFrame = 35;
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}
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else if (width * height <= 1280 * 720)
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{
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// 720p
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baseBitratePerFrame = 87;
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}
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else if (width * height <= 1920 * 1080)
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{
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// 1080p
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baseBitratePerFrame = 173;
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}
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else
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{
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// 4K and above
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baseBitratePerFrame = 347;
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}
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}
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else
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{
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if (width * height <= 352 * 288)
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{
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// CIF or smaller
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baseBitratePerFrame = 10;
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}
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else if (width * height <= 640 * 480)
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{
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// VGA
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baseBitratePerFrame = 27;
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}
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else if (width * height <= 1280 * 720)
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{
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// 720p
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baseBitratePerFrame = 67;
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}
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else if (width * height <= 1920 * 1080)
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{
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// 1080p
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baseBitratePerFrame = 133;
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}
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else
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{
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// 4K and above
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baseBitratePerFrame = 267;
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}
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}
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_maxBitrate = baseBitratePerFrame * framerate * 1000; // Convert to bps
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if (!_inited)
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{
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_currentBitrate = _maxBitrate/4;
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_maxFramerate = _framerate = framerate;
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_inited = true;
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}
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}
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}
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}

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