Half-Life: Opposing Force is an expansion pack for the popular first-person shooter Half-Life, developed by Gearbox Software and released by Valve Software in October 1999.
The expansion’s single-player mode features the same setting as the original, with the twist that the player is cast not as Gordon Freeman, but as Corporal Adrian Shephard, a U.S. Marine. Shephard is sent into the huge underground Black Mesa Research Facility on an undisclosed mission, but things go wrong and he finds himself fighting for survival against sinister government agents and monstrous aliens.

Notes:
Music has been disabled for compatibility purposes.
If you want music – go to /Library/Preferences/Half-Life OpposingForce (BlueShift) Preferences/ – open the config file with TextEdit – scroll down to the last line and delete -wavonly.
This will enable mp3 music but disable correct output of wave sounds. To fix wave output go to /Applications/Utilities/Audio-MIDI Setup – select the output source and set it to 48000 Hz , 24 Bit 2 Channel. (Note that this must be repeated every time you restart your Mac.)
If you can live without music, just leave the game as it is.

Known Issues:
See the NOTES section above – note that if you block the app with LittleSnitch you will not be able to successfully load a multiplayer map.

Pics:

Please note that this game has not been tested on Macs with GMA 950 chips, but it is likely to work.

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