OMT Mini

Every Open Media Transport tool you need on Windows, in one tray icon. Viewer, multiviewer, screen capture, virtual webcam and source management, in a 1 MB executable that idles at effectively zero CPU.

Open Media Transport is the open, royalty free video over LAN protocol published by vMix and the OMT contributors, and an alternative to NDI that costs nothing to implement. OMT Mini is a complete set of everyday tools for it, as one small program rather than several.

If you know NDI Tools, you already know what this is.

All of it from one tray icon, one install, one thing to update.

Every source opens in its own window. Open as many as you like.

• Colour conversion and scaling run in a pixel shader, so a 1080p60 feed costs almost no CPU
• Audio monitoring with per channel dBFS meters, volume and mute
• Tally display, red for program and green for preview, as lamps and a strip along the top of the window
• Statistics panel: frame rate, bitrate, decode time, dropped frames, the sender's own product name and the address it is on
• Quality suggestion sent upstream, and a low bandwidth mode that pulls the sender's one eighth preview stream instead of the full feed
• Full screen, always on top, frame and connection metadata

One window showing many sources at once, in 2x2, 3x2, 3x3, 4x3, 4x4, or the classic hero shapes 1 + 5 and 1 + 7.

• Click any cell to choose what goes in it
• Tally borders the whole cell
• Full screen on F11 or a double click, and it can open at startup straight into full screen
• Tiles use OMT's preview mode by default, the sender's own one eighth stream, so sixteen tiles cost a fraction of sixteen full feeds
• When the pointer stops moving the controls and labels fade away and you are left with nothing but pictures

The wall can be sent to the network as a single OMT source. One machine builds it, every other machine just receives it, and it does not need the window open to do that, so a spare box can compose a wall headless and hand it to the gallery.

Publishes a monitor as an OMT source using DXGI Desktop Duplication, at 50 fps by default, with optional mouse cursor and system audio via WASAPI loopback. It shows the address other machines should use to reach it, with a Copy button.

Receives an OMT source and presents it to other applications as a normal camera called "OMT Mini Virtual Camera", so a network feed can go into Teams, Zoom, OBS or anything else that takes a webcam. Registers under HKEY_CURRENT_USER, so no administrator prompt.

Sources on the local network appear automatically. The list tells you what each one is: this machine for your own, direct for one you added, the product it reports itself to be, green for another OMT Mini, and a green or red dot for whether an added source is answering.

For a sender this network cannot see, on another subnet, at the far end of a VPN, or on a host with mDNS blocked, add it by address. Leave the port off and OMT Mini finds every sender on that machine, walking the port range and confirming each one is really an OMT sender before saving it.

Added sources can then be announced on mDNS, which makes them visible to vMix and everything else that browses for OMT sources, with no video passing through this machine.

A page served by OMT Mini itself, for driving it from a browser on another machine. Off by default, turned on under Settings > Web.

It is beta: the newest part of this and the one most likely to still have rough edges. Everything else here has been through more use.

• Every open viewer and the multiview drawn where they actually are, to scale, across your real monitor layout
• Drag a window to move it, the corner to resize, double click to maximise, and the window on the machine follows
• Drag a source from the list onto a window to retarget it, or onto empty desktop to open a new viewer
• Drag sources onto the multiview cells, and change its layout
• Add a source by address remotely, including the port walk

Nothing to install at the other end and no dependencies: it is one page served from memory.

It is built to stay out of the way. The whole server is a single non-blocking loop, so there are no per connection threads to leak or fail to create; connections, request sizes and the command queue are all capped; and every connection has a deadline, so a client that stalls cannot pile up. Nothing a request touches belongs to the interface: the page and the state are strings prepared on the interface thread, and commands are queued for it to apply, so a browser can never reach a window directly.

This machine. Settings > About checks the public GitHub releases and installs the latest stable build in one press, verified against its published checksum before it runs. Checking and installing are deliberately separate: the launch check only tells you, and nothing restarts on its own, because a machine that is on air should never restart itself.

Every other machine. The control panel lists every other OMT Mini on the network, the version each is running, and which are behind, and offers to update one from there. The list costs nothing: each copy already stamps its version into the sender information OMT carries. Where a copy has its control panel on, it says so through a <OMTMiniControl> element in connection metadata, which is how this machine knows where to reach it.

Updating another machine is one deliberate press behind a confirmation that names the machine and both versions and warns you not to do it to something on air. It is not a cascade: nothing updates because a neighbour did. A machine with its control panel off cannot be updated remotely at all, which falls out of the panel being off by default and is worth keeping.

Download the latest release:

• OMTMini-Setup-<version>.exe (8.7 MB) installs to %LOCALAPPDATA%\Programs\OMT Mini. It writes nothing outside your user profile, so no administrator prompt, at install or ever after.
• OMTMini-<version>-win64.zip (3.8 MB) is the same files, portable. Unzip and run OMTMini.exe.

Windows 10 or 11, 64 bit. Settings and logs live in %APPDATA%\OMT Mini. To remove it, use Apps & features, or run OMTMini.exe --uninstall.

Most of the download is the official libomt.dll and libvmx.dll from the Open Media Transport project, redistributed unmodified. OMT Mini itself is 1 MB.

Left click the tray icon for the source list. Right click it for a menu: sources, multiview, desktop capture, the webcam output and settings.

Keyboard, in a viewer or the multiview:

Press + in the source list, or use Settings > Sources.

Leaving the port off walks upward from 6400, gives up after ten ports with nothing on them, and resets that budget every time it finds something, so a machine with senders spread across the range is still covered. Each hit is confirmed as a real OMT sender, not merely an open port, and named after what it reports itself to be.

Click an entry to select it and it offers Edit and Remove. Only sources you added by hand can be changed: a discovered one is not yours to delete, and would come straight back.

A source you added by address is one this network could not see. vMix and every other OMT tool find sources by browsing mDNS, so Settings > Sources > Announce direct sources over mDNS puts them there. They then appear in those applications by name, like any other source, with nobody typing an address.

On by default. Turn it off and each entry gets its own Announce button.

No video passes through this machine. Each announcement is a sender that carries nothing and redirects to the machine the source actually lives on, which is what OMT calls a virtual source. Whatever connects is sent straight to the original host for the pictures, so this machine is not in the media path and adds no latency or bandwidth.

Only added sources are announced. Anything already discovered is already on mDNS, and a machine that picks up one of these announcements sees it as a discovered source rather than an added one, so it will not announce it onward.

A source added without a name is called Direct source and can be renamed. It is deliberately not named after its address: a dot ends a label in DNS-SD and libomt does not escape them, so anything named after an IP is not announced at all.

OMT Mini's senders bind to TCP 6400 to 6600 by default, which you can change under Settings > Network. Allow that range, and mDNS on UDP 5353 for discovery.

Other applications only see the camera once its DirectShow filter is registered. The installer offers to do it, or use Settings > Webcam > Register. Registration writes to HKEY_CURRENT_USER only, which is why it needs no elevation, and Unregister or uninstalling undoes it.

The repository builds with no downloads: the libomt.h it compiles against is vendored, and libomt.dll is loaded at runtime rather than linked.

Cross compiling from Linux with mingw-w64 is the tested path, and is how the releases are built:

sudo apt install mingw-w64 cmake zip
./scripts/cross-build.sh

On Windows with MSVC and CMake, which is not exercised by the releases:

cmake -B build
cmake --build build --config Release

To run it, put libomt.dll and libvmx.dll next to OMTMini.exe. ./scripts/fetch-omt.sh downloads them from the official libomtnet release, or take them from a release archive. They are not committed here, so this repository stays free of binaries you would have to take on trust.

Releases here are built exactly this way, from Linux, and published with their checksums. The workflows in .github/ do the same and are there for forks.

Release artifacts, the portable zip and the installer, in dist/:

./scripts/fetch-omt.sh && ./scripts/cross-build.sh && ./scripts/package.sh

The shell scripts need bash. On Windows use Git Bash or WSL.

About 14,700 lines of C++17 against raw Win32, Direct2D and Direct3D 11, with no framework and no package manager. The only runtime dependencies are Windows itself and the two OMT DLLs.

• The virtual camera is the least proven part. A DirectShow filter is loaded into other applications' processes and behaviour varies between hosts, so treat it as beta. If an application does not see the camera, please open an issue saying which application and which Windows version.
• 64 bit host applications only for the camera. A 32 bit one will not find it.
• P216 and PA16 high bit depth formats are received by libomt but not yet rendered, so they are not offered.
• Desktop capture sends at the monitor's native resolution.
• Multiview has no audio, on screen or sent. It is a wall, not a monitoring position.
• An added source addresses one sender. Listing everything on a remote host needs a discovery server, which is the only remote enumeration libomt offers.
• The reachability dot means a TCP connection was accepted, not that an OMT sender is behind it. The port walk goes further and confirms each hit.
• The control panel is beta, and has no password. Anyone who can reach its port can move, retarget and close windows on that machine. It is off by default and should only be turned on where you trust the network.
• Windows only. The protocol is cross platform and so is most of the logic, but the interface, capture and camera layers are Win32.

Issues and pull requests are welcome, particularly reports of applications that do not get on with the virtual camera. No contributor licence agreement, no style config to install; match the surrounding code.

MIT licensed, see LICENSE.

Uses libomt and libvmx from the Open Media Transport project, MIT licensed and redistributed unmodified in the release archives. Their licence is included as LICENSE-libomt.txt.

Not affiliated with, endorsed by, or supported by vMix (StudioCoast Pty Ltd) or the Open Media Transport project.