RoomRelay

RoomRelay is an open-source Windows app for streaming system audio or a single application's audio to Sonos speakers on your local network.

It is built for the gap Sonos does not cover directly on Windows: live PC audio from browsers, music apps, games, calls, media players, or any other audio source that Windows can capture. It works best for music, podcasts, radio, and background audio where a small network buffer is acceptable.

Download

Download the latest release from the releases page:

• Windows x64 (Intel/AMD): installer (RoomRelay-Setup-…-win-x64-full.exe) or portable ZIP (RoomRelay-…-win-x64-full.zip).
• Windows on ARM (Snapdragon, Surface Pro X, etc.): installer (RoomRelay-Setup-…-win-arm64-full.exe) or portable ZIP (RoomRelay-…-win-arm64-full.zip).
• A -light variant of each is also published; it omits the bundled Windows App Runtime and requires the matching framework package to be installed separately.
• SHA256SUMS.txt lists checksums for every artifact.

The full release build bundles the app and .NET runtime. It uses the installed Windows App Runtime framework package on Windows.

Why RoomRelay?

Sonos supports many music services directly, and Windows Media Player can cast media-library files to Sonos, but live Windows system/app audio is still awkward. RoomRelay gives that use case a native, open-source Windows app.

Option	Windows live system audio	Per-app audio	Open source	Notes
RoomRelay	Yes	Yes	Yes	Native WinUI 3 app for Sonos over LAN
Stream What You Hear	Yes	No	Yes	Older DLNA-style app; targets .NET Framework
TuneBlade	Yes	No	No	AirPlay-oriented; best with AirPlay-compatible Sonos models
Airfoil	No current Windows app	No current Windows app	No	Current Sonos support is Mac-focused; Windows version was retired
foobar2000 UPnP output	No	No	No	Useful for playing foobar/library audio to UPnP renderers; not live system/app audio
Windows Media Player	No	No	No	Casts local library files, not live system/app audio

Features

• Stream the default Windows audio output to a Sonos room.
• Stream audio from a selected application on supported Windows versions.
• Discover Sonos speakers on the local network.
• Collapse stereo pairs into one selectable room.
• Built-in volume, per-channel gain, EQ, delay, VU, and spectrum tools.
• Sonos volume control that moves the whole zone group, keeping each room's relative level.
• Stable and low-latency streaming modes, with a lossless WAV PCM option for users willing to trade bandwidth for lower buffering.
• The encoded stream is paced against a wall clock, so a capture hiccup or an idle PC cannot slowly starve the speaker's buffer.
• Per-application format and latency preferences are remembered when the app session appears again.
• Tray icon with show/quit actions and close-to-tray behavior.
• Single-instance behavior: launching RoomRelay again restores the existing window instead of opening a duplicate instance.
• No FFmpeg, no NAudio, and no third-party audio runtime dependency. AAC encoding, sample-rate conversion, and WASAPI capture use Windows APIs.

Known limitations

• RoomRelay is for local-network Sonos streaming. It is not a remote access or cloud streaming tool.
• Like most network Sonos streaming approaches, it is not intended for low-latency gaming or video sync.
• AAC is the recommended default and may have several seconds of Sonos buffering latency, because Sonos pre-buffers the stream as internet radio. WAV PCM is noticeably lower latency but uses about 1.5 Mbps and is more sensitive to Wi-Fi or older Sonos hardware.
• Per-application capture depends on Windows process-loopback support and is best on current Windows 11 builds.
• The first run may require allowing the Windows Defender Firewall prompt on the private network where your Sonos speakers live.
• The local stream is not encrypted or authenticated. Use RoomRelay only on trusted private networks.

Feedback

Bug reports and feature requests are welcome in GitHub Issues. General ideas, speaker compatibility reports, and setup notes belong in GitHub Discussions.

Reporting issues

RoomRelay can create a diagnostics package from the app. Use Create package in the Diagnostics section, or right-click the tray icon and choose Create diagnostics package. Attach that ZIP when reporting discovery, streaming, or per-application capture problems.

The package includes RoomRelay logs, crash details if present, app/Windows version info, current source/format, discovered-speaker counts, and network adapter details. It may include local IP addresses, Sonos room names, device UDNs, and process names, so review it before posting publicly.

Logs are stored in %APPDATA%\RoomRelay. The tray menu also has Open logs folder for manual access.

Requirements

	Minimum	Recommended
OS	Windows 10 22H2	Windows 11 23H2 or later
Architecture	x64 or ARM64	x64 or ARM64
Runtime	Bundled in the -full artifacts	Bundled in the -full artifacts

RoomRelay targets .NET 10 and WinUI 3 via the Windows App SDK 2.0. The -full release artifacts carry the .NET runtime, so only the Windows App Runtime framework package is resolved from the system, and Windows 11 normally already has it. The -light artifacts omit the bundled runtime.

Minimal dependencies. There is no FFmpeg, no NAudio, and no third-party audio runtime. Capture, resampling, and AAC encoding all go through Windows APIs (WASAPI and Media Foundation) via CsWin32-generated bindings.

Why Windows 11 is recommended

• Process loopback (ActivateAudioInterfaceAsync for per-app capture) requires Windows 10 21H2 or later. On Windows 10 this feature may be unavailable or unstable depending on patch level.
• WinUI 3 performance and compatibility are best on Windows 11.
• WASAPI shared-mode loopback works on both, but the developer test matrix is Windows 11-only.

Quick start

Install RoomRelay from the installer, or extract the ZIP and run RoomRelay.exe. Settings are stored in %APPDATA%\RoomRelay.

Prefer an installer? See csharp/installer/ for an Inno Setup script that builds a standard Windows .exe installer with shortcuts and clean uninstall.

Recommended settings

Use case	Format	Latency mode	Notes
Music, podcasts, radio	AAC 256 kbps	Stable	Recommended default; most tolerant of Wi-Fi and older speakers.
Casual video	WAV PCM	Low latency	Lower buffering, but high bandwidth and model/network dependent.
Unstable Wi-Fi	AAC 128/192/256 kbps	Stable	Prefer AAC and avoid PCM until the network is reliable.
Older Sonos hardware	AAC 256 kbps	Stable	PCM may fail, stutter, or buffer for a long time.
Per-application capture	Start with AAC 256 kbps	Stable	Switch to Whole system if the app is protected, elevated, browser-isolated, or silent.

Latency modes

• Stable keeps larger capture and PCM batching buffers. Use it when audio quality and reliability matter more than delay.
• Low latency uses smaller WASAPI and PCM buffers. It can reduce delay for WAV streams, but it is more sensitive to packet loss, slow writes, and Sonos model behavior.
• RoomRelay still cannot bypass Sonos' own network buffering. It is not a replacement for HDMI, analog speakers, or gaming/headset audio.

Format compatibility

• AAC is the safest Sonos path and remains the default. Sonos treats it as an internet radio stream, which is reliable but adds around a second of pre-buffering.
• WAV PCM is lossless 48 kHz stereo in a streaming WAV container, served as audio/wav. It uses about 1.5 Mbps and gives noticeably lower latency than AAC, because Sonos does not apply radio-style pre-buffering to it.

Why there is no L16 PCM option

Earlier versions offered an L16 PCM mode: the same 16-bit samples in network byte order with no container, served as audio/L16. It never worked, and it was removed rather than fixed.

audio/L16 is a standard type (RFC 2586) and is common in UPnP and DLNA renderers, but Sonos does not implement it. Asking a speaker directly settles it: ConnectionManager GetProtocolInfo returns the list of formats a player can decode, and on a Sonos One SL, a Beam, and an Arc that list has 65 entries with no audio/L16 among them. The only PCM entries are audio/wav and audio/x-wav.

The failure was quiet and easy to misread. SetAVTransportURI and Play both succeed, because Sonos does not check the content type until it opens the stream. It then reads a single chunk, fails to find a decoder, and closes the connection, so the app looked like it was streaming while the room stayed silent.

Nothing is lost by removing it. WAV PCM carries identical audio, differing only by a 44-byte header per connection and byte order, and it is the format Sonos actually supports. If an older settings.json still selects L16 PCM, RoomRelay migrates it to WAV PCM on startup. See issue #32.

Troubleshooting discovery

• Allow the Windows Defender Firewall prompt on the private network where Sonos lives.
• Keep the PC and Sonos on the same subnet/VLAN when possible. SSDP discovery often fails across guest networks, VLAN boundaries, and some mesh isolation modes.
• Disable VPNs or split-tunnel rules that hijack local multicast traffic.
• Use Add by IP if discovery misses a room. Most Sonos speakers expose the device-description endpoint on port 1400.
• Create a diagnostics package when reporting problems. It includes network adapters, selected room, local stream IP, format, latency mode, and timing counters.

Per-application capture

• Per-app capture uses Windows process loopback and is best on current Windows 11 builds.
• Some browsers, protected media apps, elevated processes, system apps, and short-lived sessions may not be capturable.
• If the per-app list is empty, start playback in the target app, wait a few seconds, then click Refresh apps.
• Enable Show all audio sessions to reveal advanced entries that RoomRelay normally hides. These entries can help diagnose empty-list reports, but some of them may still fail Windows process-loopback capture.
• Use Whole system mode when the target app does not appear or cannot be captured per-application.
• RoomRelay remembers the last selected app by process name and restores that app's preferred format and latency mode when it appears again.
• Diagnostics packages include the latest per-app enumeration counts, including total sessions, filtered sessions, system sessions, and kept app sessions.

Compared with other approaches

Option	Strength	Tradeoff
RoomRelay	Native Windows live/app audio to Sonos without AirPlay or Bluetooth	Local-network only; Sonos buffering still applies.
AirPlay from Windows apps	Useful when a Windows app exposes AirPlay directly	Model-specific failures are common, and not all Sonos devices support AirPlay.
Bluetooth	Simple on speakers that support it	Not available on many Sonos speakers and does not integrate cleanly with groups.
Sonos line-in	Hardware-supported path on compatible Sonos devices	Requires line-in hardware and still has Sonos buffering delay.
Stream What You Hear	Older Windows workaround	Abandoned/legacy feel and no per-application capture.

What it does

• Captures the default Windows render endpoint via WASAPI loopback or a specific application's audio output via process loopback (ActivateAudioInterfaceAsync on the VAD\Process_Loopback virtual device).
• Resamples / converts to 48 kHz 16-bit stereo (pure-C# pass-through when the device already mixes at 48 kHz; otherwise the Windows Media Foundation resampler MFT, CLSID_CResamplerMediaObject).
• Encodes to AAC-LC @ 256 kbps using the Windows Media Foundation AAC encoder MFT (CLSID_CMSAACEncMFT) configured with MF_MT_AAC_PAYLOAD_TYPE = 1 so the output is already ADTS-framed.
• Serves the ADTS stream on http://<host>:8000/stream/<token>.aac from a raw TcpListener HTTP/1.0 server (no chunked encoding, which Sonos rejects). The token is random per run, and the server binds to the interface that routes to the chosen speaker rather than to all interfaces.
• Discovers Sonos speakers via SSDP M-SEARCH on every usable network interface — IPv4 (239.255.255.250) and IPv6 (ff02::c) — with concurrent per-socket receive loops. Resolves user-set zone names from ZoneGroupTopology so the UI shows "Living Room" instead of RINCON_….
• Resolves Sonos topology so stereo pairs, grouped rooms, and mixed S1/S2 households are shown as playable room/group targets.
• Pushes the stream URL to the chosen speaker via UPnP SOAP (SetAVTransportURI with the x-rincon-mp3radio:// prefix, then Play).
• Mutes the default render endpoint while streaming so the room doesn't hear PC audio twice (loopback captures pre-mute, so Sonos still gets data).
• Paces the output against a wall clock. WASAPI loopback delivers nothing at all while the PC is silent, and a busy machine can drop capture buffers, so the stream would otherwise run slowly short of real time until the speaker's buffer drained. A rate governor compares what has been produced against what the clock says should exist, fills any shortfall with silence, and skips a buffer if output ever runs ahead. AAC hides small shortfalls because Sonos resyncs on ADTS frames; raw PCM has no framing and simply stalls, which is why this matters most for WAV.

UI

WinUI 3 window with Mica backdrop and declarative XAML UI:

• Speaker list with Rescan and auto-select on launch (last speaker remembered by UDN).
• Grouped rooms and stereo pairs are shown as one selectable Sonos playback target because Sonos accepts playback commands on the group coordinator.
• Source picker: Whole system or Per application (combo populates from active audio sessions, refreshed every 2 s).
• Start / Stop with ProgressRing busy state and mutual disable.
• Stream volume (0–8× with soft clip), balance, per-channel L/R gain with Link, 3-band EQ, per-channel delay — all in collapsible Expander sections. These are RoomRelay DSP controls; they do not change Sonos device volume or tone.
• Sonos device volume can be refreshed and applied separately through Sonos GroupRenderingControl, so changing it moves every room in the group while preserving their relative levels. Players that do not expose the group service, such as bonded satellites, fall back to per-player RenderingControl.
• Live VU meter and spectrum analyzer (Win2D, 30 fps).
• InfoBar error notification when the pipeline crashes or the audio endpoint format changes.
• Tray icon with Show / Quit; close-to-tray on window X.
• All slider positions and the last speaker persist to %APPDATA%\RoomRelay\settings.json with debounced disk writes (no more hundreds of file writes per slider drag).

Security and privacy notes

• This is an unofficial Sonos utility and is not affiliated with or endorsed by Sonos.
• While streaming, the app runs a local HTTP server so the selected Sonos speaker can fetch the audio. The server binds to the local network interface used to reach that speaker and uses a random per-run stream path.
• The stream is not encrypted or authenticated. Only allow the Windows Defender Firewall prompt on trusted private networks.
• Settings are stored locally under %APPDATA%\RoomRelay. They may include the last selected speaker UDN, but no audio is recorded to disk by the app.

Building from source

Prerequisites

• .NET 10 SDK.
• Windows App Runtime 2.0 framework package (run Get-AppxPackage *WindowsAppRuntime.2.0* to check).
• That's it — no extra DLLs to drop in.

Build & run

cd csharp
dotnet build -c Release
dotnet run --project src/SonosStreaming.App

First run will trigger a Windows Defender Firewall prompt — allow on the network profile where your Sonos lives so it can fetch the stream.

Architecture

csharp/
  SonosStreaming.sln
  Directory.Build.props        # net10.0-windows, x64, unsafe, C# preview
  src/
    SonosStreaming.Core/        # audio, network, DSP, pipeline
      Audio/                    # WASAPI capture, MF encoder, resampler, DSP
      Network/                  # SSDP, SOAP, HTTP stream server
      Pipeline/                 # PipelineRunner orchestration
      State/                    # AppCore state machine, AppSettings
    SonosStreaming.App/         # WinUI 3 unpackaged desktop app
      Views/                    # MainPage.xaml (declarative, x:Bind)
      ViewModels/               # MainViewModel (CommunityToolkit.Mvvm)
      Controls/                 # VuMeterControl, SpectrumControl
      Converters/               # BoolToVisibilityConverter
      Tray/                     # H.NotifyIcon + native PopupMenu
  tests/
    SonosStreaming.Tests/       # xUnit + FluentAssertions + FsCheck

Data flow

WASAPI / process-loopback capture → PcmFrameF32
                                        ↓
                  DSP (gain → EQ → delay → volume → VU → spectrum)
                                        ↓
                            Resampler (f32 → i16 @ 48 kHz)
                                        ↓
              OutputRateGovernor (pads or trims against the wall clock)
                                        ↓
           MfAacEncoder (Media Foundation MFT)  |  LpcmEncoder (WAV)
                                         ↓
                        BroadcastChannel<ReadOnlyMemory<byte>>
                                        ↓
                          StreamServer (TCP, HTTP/1.0)
                         /             |             \
                   Sonos conn     Sonos conn       ...

Testing

cd csharp
dotnet test

Unit tests use xUnit + FluentAssertions + FsCheck. The e2e test (MockSonosE2E.cs) spins up a mock Sonos HTTP + SOAP server on 127.0.0.1:0.

Status

End-to-end working: whole-system capture, per-application capture, real-time DSP, AAC and lossless WAV PCM streaming to a Sonos speaker, stereo pair, or zone group, group-wide volume control, endpoint-mute-while-streaming, wall-clock output pacing, settings persistence with debounced saves, tray icon, native context menu, clean shutdown, pipeline crash recovery with user-visible errors, audio endpoint format-change detection, and dual-stack IPv4/IPv6 SSDP discovery. Audio backend is FFmpeg-free and NAudio-free, using only Windows-native APIs. Builds with zero warnings.

Stream rate measured against real hardware, where nominal is the exact byte rate the declared format implies:

format	duration	delivered	vs nominal
AAC 256	621.8 s	31,998 B/s	99.995%
AAC 320	539.5 s	39,995 B/s	99.99%
WAV PCM	301.2 s	192,015 B/s	+0.008%

License

MIT OR Apache-2.0.