Nageru and Futatabi

Nageru user interface, during a sports event

This page describes Nageru, a modern free software video mixer, and Futatabi, a multi-camera free software instant replay system with slow motion. They are separate applications, but are made to work efficiently together and share a fair amount of source code, so they are also distributed together.

Nageru (投げる), a modern free software video mixer

Nageru (a pun on the Japanese verb nageru, meaning to throw or cast) is a live video mixer. It takes in inputs from one or more video cards (any DeckLink PCI card via Blackmagic's drivers, and Intensity Shuttle USB3 and UltraStudio SDI USB3 cards via bmusb), mixes them together based on the operator's desire and a theme written in Lua, and outputs a high-quality H.264 stream over TCP suitable for further transcoding and/or distribution. Nageru is free software, licensed under the GNU General Public License, version 3 or later.

Nageru aims to produce high-quality output, both in terms of audio and video, while still running on modest hardware. The reference system for two 720p60 inputs is a ThinkPad X240, ie. an ultraportable dual-core with a not-very-fast GPU. Nageru's performance scales almost linearly with the available GPU power; e.g., if you have a GPU that's twice as fast as mine (which is not hard to find at all these days; desktop GPUs are frequently more like 10x), going to 1080p60 will only cost you about 10% more CPU power.

Various real-world examples of videos produced by Nageru:

Futatabi (再び), a multi-camera free software instant replay system with slow motion

Futatabi is a multi-camera instant replay system with slow motion. It supports efficient real-time interpolation using optical flow, making for full-framerate output without having to use special high-framerate cameras. (Of course, interpolation can only take you so far, and the results will depend on the type of content.) Futatabi is currently in alpha. It is distributed and built together with Nageru.


Nageru and Futatabi have extensive documentation at In addition, you can see the FOSDEM 2016 talk introducing Nageru, although it covers only 1.0.0 and a lot of things have happened since then:

There was a talk about Futatabi at FOSDEM 2019, too (covering 1.8.2):


Contact information at my home page.