Steam Community link

With certain games that use MCI for CD audio (i.e. Quake I/II, Heretic II), the BGM tracks won't loop if you're using Win 7. The exe and Win7's MCI don't play nice with each other. But there's a workaround. Head here and get the _inmm.dll Ver 2.38 (287 KB). Install.

Rip the soundtrack from your game CD to MP3 files (or maybe even Ogg Vorbis, which I hadn't tried).

Drag and drop your Quake client exe (or Quake2.dll for Heretic II) onto the _inmmcnf.exe file to have it patched. A backup of your patched exe or dll will be made as an .org file. Next, run _inmmcnf.exe itself to configure it. On the Method tab, set Default to DirectShow. Use the _inmm.ini tab to add your ripped BGM tracks to the configuration. There is no need to use a dummy "Track01".

Save your _inmm.ini to the game's folder. Next time you play, the game should play its BGM from the MP3s and properly loop them.

I tried it with H2 and the BGM no longer cuts out during a level. Thanks to Dragonsbrethren for the fix.