0.3.1 — CI modernization: Swift 6.2/6.3 matrix, GitHub Actions node24

What's Changed

CI modernization

• Swift 6.2 + 6.3 matrix — Build and test matrix on macOS (Xcode 26.2 / Xcode 26.4) and Linux (swift:6.2 / swift:6.3) with fail-fast: false for full coverage of both toolchains
• Codecov deduplication — Coverage upload restricted to the Swift 6.2 slot to avoid duplicate reports
• GitHub Actions node24 migration — All actions bumped to the minimum major version running on node24, ahead of GitHub's node20 deprecation:

Action	From	To
actions/checkout	v4	v5
actions/upload-artifact	v4	v6
actions/download-artifact	v4	v7
codecov/codecov-action	v5	v6
actions/upload-pages-artifact	v3	v4
actions/deploy-pages	v4	v5
softprops/action-gh-release	v2	v3

• Xcode 26.4 — DocC deploy and release workflows now build with Xcode 26.4 (Swift 6.3)
• Linux release binary — Release workflow builds with swift:6.3 container

No code changes

This release contains CI/infrastructure changes only. The SRTKit library, CLI, and all public APIs are unchanged from 0.3.0.

Compatibility

• Swift 6.2 (Xcode 26.2) — fully supported
• Swift 6.3 (Xcode 26.4) — fully supported, zero warnings
• All 2166 tests pass on both toolchain

New Contributors

• @Sweefties made their first contribution in #1

Full Changelog: 0.3.0...0.3.1

0.3.0 — Data Packet Fix, ACK/ACKACK & Random ISN

Highlights

This release fixes critical protocol-level bugs that prevented data packets from being accepted by SRT receivers (libsrt, MediaMTX, gosrt). The root cause was a combination of duplicate message numbers, missing ACK handling, and static Initial Sequence Numbers. All fixes have been validated end-to-end against MediaMTX v1.16.3 with tcpdump wire-level comparison against the reference libsrt 1.5.4 implementation.

What's New

Data Packet Message Number (ROOT CAUSE)

• Each send() now increments the message number (was always 0)
• In SRT Live mode (PP=11, single message per packet), the receiver uses messageNumber for deduplication — all packets with messageNumber=0 were silently dropped as duplicates after the first
• Wire-validated against libsrt: message numbers now match the baseline (1, 2, 3, ... wrapping at UInt26 max)

ACK/ACKACK Handling

• Incoming ACK packets are now parsed (ACK CIF: lastACKedSequenceNumber)
• ACKACK responses sent back to the peer (control type 0x0006, echoing ACK sequence number)
• Send buffer properly released via pipeline.processACK()
• Fixes send buffer overflow that occurred after ~47 seconds of streaming

Random Initial Sequence Number (ISN)

• Caller, Listener, and Rendezvous handshakes now generate a random 31-bit ISN per IETF draft-sharabayko-srt §4.3
• Separate ISN for send and receive directions (localInitialSequenceNumber for send, initialSequenceNumber for receive from peer)
• Previously, ISN was always 0 and shared for both directions

Listener Extension Flags

• Conclusion Response extension flags now dynamically include .kmreq when a KMRSP (Key Material Response) is present
• Fixes encryption negotiation with callers that send KMREQ

Bug Fixes

Bug	Impact	Root Cause
messageNumber always 0	Critical	All data packets dropped as duplicates by receiver
ACK ignored, no ACKACK	Critical	Send buffer overflow after ~47s
ISN always 0, shared send/receive	Critical	Data packets with wrong sequence numbers
Listener extension flags hardcoded	High	KMRSP not advertised in Conclusion Response

Diagnostic Methodology

The root cause was identified through wire-level tcpdump comparison between libsrt 1.5.4 (baseline) and swift-srt-kit:

Baseline word1: c000 0001 → PP=11, messageNumber=1 ✓
Swift word1:    c000 0000 → PP=11, messageNumber=0 ✗ (all packets dropped)

The receiver (libsrt in MediaMTX) accepted the first packet as message 0, then dropped every subsequent packet as a duplicate of message 0.

Stats

• 2,166 tests across 204 suites — all passing
• 0 warnings (swift build, xcodebuild, DocC, SwiftLint, swift-format)
• E2E validated: 3 min H.264+AAC MPEG-TS → MediaMTX v1.16.3 → ffplay, 0 errors, 0 buffer overflow
• Wire-validated: tcpdump comparison against libsrt 1.5.4 reference implementation

Server Compatibility

Server	StreamID Format	Status
MediaMTX v1.16+	publish:path	Tested E2E
libsrt receivers	#!::r=path,m=publish (SRT Access Control)	Compatible
Haivision SRT Gateway	#!::r=path,m=publish	Compatible

Note: MediaMTX uses its own StreamID format (action:pathname) instead of the SRT Access Control spec (#!::r=pathname,m=action). The StreamID is user-configurable via SRTCallerConfiguration.streamID.

Migration

No breaking API changes. The HandshakeResult struct has a new localInitialSequenceNumber field with a default value of SequenceNumber(0), preserving backward compatibility for existing code.

Full Changelog: 0.2.0...0.3.0

0.2.0 — IPv6 Support & libsrt Interoperability

What's New

IPv6 Support

SRTCaller and SRTListener now fully support IPv6 addresses. Previously, connecting to localhost on macOS failed because it resolved to ::1 (IPv6) while the socket was bound to IPv4 only. Both caller and listener now detect the address family and bind accordingly.

StreamID Wire Format Fix

StreamIDExtension encode/decode now correctly inverts bytes per 4-byte chunk as required by the SRT protocol specification. This fixes interoperability with all libsrt-based implementations including MediaMTX, OBS Studio, ffmpeg, and srt-live-transmit. Previously, stream IDs were scrambled when communicating with non-swift-srt-kit peers.

Note: This is a breaking change for swift-srt-kit ↔ swift-srt-kit connections that rely on StreamID. Both peers must upgrade to 0.2.0.

Changes

• SRTPeerAddress.from(_:) — new static method for proper IPv4/IPv6 socket address extraction
• SRTCaller.setupTransport() — binds :: for IPv6, 0.0.0.0 for IPv4
• StreamIDExtension.encode() — each 4-byte group written as UInt32 word per SRT spec
• StreamIDExtension.decode() — each 4-byte group read as UInt32 word per SRT spec
• Version bumped across CLI, documentation, and README

Compatibility

• Swift 6.2+
• macOS (arm64, x86_64), Linux (x86_64)
• 2,166 tests passing

Full Changelog: 0.1.0...0.2.0

0.1.0 — Initial Release

Pure Swift implementation of the Secure Reliable Transport (SRT) protocol. No C dependencies — this is not a libsrt wrapper.

Highlights

• Pure Swift — zero C dependencies, complete protocol implementation from UDP up
• Interop validated — bidirectional encrypted communication with libsrt 1.5.4
• 2163 tests across 204 suites, 96%+ code coverage
• Cross-platform — macOS, iOS, tvOS, watchOS, visionOS, and Linux

Connection Modes

• SRTCaller — connect to a remote SRT listener
• SRTListener — accept incoming SRT connections
• Rendezvous — simultaneous peer-to-peer connection

Encryption

• AES-CTR and AES-GCM cipher modes (128/192/256-bit keys)
• PBKDF2 key derivation (RFC 2898)
• RFC 3394 AES Key Wrap for stream encryption keys
• Automatic even/odd key rotation with pre-announce

Reliability & Error Correction

• ACK/NAK-based retransmission with configurable intervals
• Forward Error Correction (FEC) — row, column, and matrix XOR recovery
• Configurable ARQ modes (always, onreq, never)
• TSBPD timing with clock drift correction and too-late packet drop

Connection Bonding

• Broadcast — send to all links simultaneously
• Main/Backup — automatic failover with stability monitoring
• Balancing — weighted aggregate across links with packet deduplication

Congestion Control

• LiveCC — packet pacing for real-time streams
• FileCC — AIMD with slow start for bulk transfers
• AdaptiveCC — pattern detection with automatic mode switching
• Pluggable architecture via CongestionControllerPlugin protocol

Bandwidth Probing

• Stepped probe engine with quick/standard/thorough presets
• Auto-configuration generation (recommended bitrate + latency)
• Real-time bitrate monitoring with hysteresis

Statistics & Monitoring

• Comprehensive metrics: packets, bytes, RTT, bandwidth, buffers, FEC, encryption
• 5-metric weighted quality scoring (excellent/good/fair/poor/critical)
• Prometheus text exposition format
• StatsD datagram export

Access Control

• StreamID parsing and generation (#!:: format)
• Resource, mode, session, user, content type, and custom keys

Configuration

• SRTConfigurationBuilder with fluent API
• 6 presets: lowLatency, balanced, reliable, highBandwidth, broadcast, fileTransfer
• Server presets: AWS MediaConnect, Nimble Streamer, Haivision, OBS, Wowza, vMix, SRT Live Server
• Full option validation with descriptive errors

Additional Features

• Auto-reconnect with exponential backoff and jitter
• Multi-caller for simultaneous multi-destination publishing
• Multi-stream multiplexing over single listener
• Stream recording with size/duration-based rotation (MPEG-TS or raw)

CLI

srt-cli with 6 commands: send, receive, probe, stats, test, info

Platforms

Platform	Minimum
macOS	14+
iOS	17+
tvOS	17+
watchOS	10+
visionOS	1+
Linux	Swift 6.2

Standards

RFC 2898 (PBKDF2), RFC 3394 (AES Key Wrap), NIST SP 800-38A (AES-CTR), NIST SP 800-38D (AES-GCM), IETF Draft SRT Protocol

Full Changelog: https://github.com/atelier-socle/swift-srt-kit/commits/0.1.0