CastMirror

Mirror your Windows PC to a Chromecast or Google TV.
Your whole screen or one window, with sound, and no Chrome.
Download for Windows · Download for Linux · Docs

Install

1. Download CastMirror-Setup-<version>-x64.exe from the latest release.
2. Run it. The installer adds a Start menu entry and a Windows Firewall rule for private and domain networks, so Windows doesn't stop discovery with a prompt.
3. Turn your TV on, put it on the same Wi-Fi as the PC, and open CastMirror.

A portable CastMirror-win-x64.zip is also on the release page. If you use it, run scripts\setup_firewall.ps1 once from an elevated PowerShell, or allow CastMirror when Windows asks.

CastMirror needs Windows 10 version 2004 or later, 64-bit. Checksums for every download are in SHA256SUMS-windows.txt.

Use it

1. Pick your TV from the device cards on Home, or from the list in the casting panel. If it doesn't appear, press Refresh (F5) or use Add by IP. Ctrl+K searches the list.
2. Under Casting options, pick what to share: the entire screen, or one application window. For a window, choose it from the list that appears.
3. Choose a quality preset on the Cast page, then press Start casting (Ctrl+Enter) or Cast on a device card.

While casting you can freeze the picture, mute the TV, and change the bitrate without restarting. Closing the window keeps the cast running in the tray. Quit from the tray icon.

Preset	Use it for	Buffer
Auto	Most things. Starts at 1080p and adapts to your Wi-Fi.	200 ms
High	A strong 5 GHz link and a TV that can take the bitrate.	200 ms
Balanced	Everyday use over average Wi-Fi.	200 ms
Smooth	Weak Wi-Fi. Drops to 720p.	200 ms
Game	Lowest delay. Keeps resolution fixed.	150 ms
Cinema	Video. Highest bitrate, deepest buffer.	400 ms

Keyboard shortcuts

In the window: Ctrl+Enter start or stop, F5 refresh devices, Ctrl+K search devices, Ctrl+, settings, Ctrl+L logs.

Optional system-wide shortcuts (Settings, Desktop integration, Global shortcuts): Ctrl+Alt+C start or stop, Ctrl+Alt+F freeze, Ctrl+Alt+M mute the TV.

What it does

• Discovers Cast devices over mDNS. If your router blocks mDNS, an opt-in subnet scan finds them directly.
• Captures a monitor with DXGI Desktop Duplication, or a single window through Windows.Graphics.Capture, at a steady 30 or 60 fps even when nothing on screen changes. Window capture shows the window's own content, so windows in front of it stay out of the picture. If a driver hands back HDR or 10-bit surfaces, they are converted to SDR.
• Captures system audio with WASAPI loopback, follows the default speakers when you switch to headphones, and folds 5.1 and 7.1 down to stereo. You can share one app's sound instead of everything (Settings, Audio, Share audio from), so notifications and other apps stay off the TV.
• Encodes H.264 on the GPU through Media Foundation and falls back to x264 on the CPU when the GPU encoder doesn't produce frames. Audio is Opus.
• Sends the same encrypted Cast RTP stream Chrome's "Cast screen" uses. The control connection is TLS on port 8009, and each device proves its identity against the Cast root certificates.
• Adapts bitrate and resolution to packet loss and round-trip time, and reconnects after a dropped connection, a sleep or a Wi-Fi change. You choose how long it keeps trying.
• Runs a single instance. Starting it again brings the running window forward.
• Optional: start hidden in the tray at sign-in, desktop notifications, light or dark theme.
• Speaks English, Spanish, German and French, following your Windows display language. The translations are unreviewed machine translations, so corrections are welcome. To try one, set CASTMIRROR_LANG=de before starting the app.

Privacy

CastMirror talks to your TV over your local network and to nothing else. It has no telemetry and no account. It contacts GitHub only when you press Check for updates in About. Logs and settings stay in %APPDATA%\CastMirror. Logs, Copy for bug report masks the last part of every IP address before it reaches your clipboard.

When something goes wrong

• No devices found. Check the PC and TV are on the same network, and that the network isn't a guest or "client isolation" network. Then try Settings, Device discovery, Scan the network for TVs.
• Windows asked about the firewall. Choose Allow for private networks. The installer normally does this for you.
• The picture glitches or stutters. Lower the preset to Balanced or Smooth, or turn on Force software encode.
• CastMirror crashed. It saves a crash file in %APPDATA%\CastMirror\crashes and tells you next launch. The file holds a copy of the program's memory, so share it only if you're comfortable with that.
• Anything else. Open Logs, press Copy for bug report, and paste it into an issue.

Build from source

Windows build steps, including the MSYS2 packages and the .NET SDK, are in docs/building.md. In short:

build-all.bat        :: native core + WinUI app
package.ps1          :: tests, self-contained publish, licence checks

Architecture notes are in docs/ARCHITECTURE.md, the Cast protocol details in docs/protocol.md, and device test results in docs/DEVICE_MATRIX.md. Contributions are welcome; see CONTRIBUTING.md.

What it isn't

• Not a Chrome or CEF wrapper.
• Not a game-streaming tool like Sunshine or Moonlight. Cast keeps a playout buffer, so expect about 150 to 400 ms of delay depending on the preset.
• Not affiliated with Google. Chromecast, Google Cast and Google TV are trademarks of Google LLC.

Linux

The same castcore engine builds on Linux with a GTK 4 app and a CLI. It has its own release, linux-v1.0.0, with a .deb and an .rpm:

sudo apt install ./castmirror_1.0.0_x86_64.deb
castmirror-gui

Capture works on X11 and, through the desktop portal, on Wayland. Video is VAAPI H.264 with an x264 fallback, and sound comes from the PulseAudio or PipeWire default sink. The Windows app is the primary product and Linux gets fixes rather than features; the Linux GUI and Wayland path were built and unit-tested for 1.0.0 but not exercised on a live desktop. Build steps are in docs/building.md.

Licence

CastMirror's source is Apache-2.0 (see LICENSE). The Windows binaries include FFmpeg and libx264, which are GPL, so the download as a whole is distributed under the GPL. The details and the source offer are in THIRD-PARTY-LICENSES.txt.