3ivx is a video codec created by 3ivx Technologies, based in Sydney, Australia.

3ivx ( "Thriv-ex") is a codec suite that allows the creation of MPEG-4 compliant data streams. It has been designed around a need for decreased processing power for use mainly in embedded systems. 3ivx provides plugins and filters that allow the MPEG-4 data stream to be wrapped by the Microsoft ASF and AVI transports, as well as Apple's QuickTime transport. It also allows the creation of elementary MP4 data streams and provides an audio codec for creation of AAC audio streams.

Official decoders and encoders are provided for Microsoft Windows, Mac OS and BeOS, with unmaintained older releases for the Amiga and Linux. In addition, FFmpeg can decode 3ivx encoded video.

The company is notable for its support of the Haiku OS, providing a port of the 3ivx codec. The 3ivx port maintainer has also produced a Quicktime MOV extractor and an MPEG-4 extractor for Haiku. As of 2005, they are the only company to support Haiku in any way.

The 30 day trial version of 3IVX is associated via Microsoft Windows operating systems to such media players as Quicktime and ITunes. Uninstalling 3IVX does not reset the 3IVX.dll file if the media players have been updated. Uninstalling and restoring the media players does not solve the problem as Windows still associates them to 3IVX.dll which is expired or been uninstalled. Therefore .mp4 files can not be played in Quicktime or ITunes where Windows is seeking the absent 3IVX.dll. Installing 3ivx MPEG-4 5.0 or greater will correct the issue (you can then uninstall if you wish).