A low-level, low-latency WASAPI audio driver has been written for RetroArch, and will likely appear in the next stable RetroArch version (1.5.1).
Windows users have requested this for a long time. Up until now, RetroArch on Windows could make use of either DirectSound (the older audio API ) or XAudio2 (available since Windows XP SP2+ and up). WASAPI has been available since Windows Vista and should allow for lower latency audio.
There are currently still some limitations in the current implementation but we are optimistic this will be ironed out :
* Some issues right now when setting the audio latency below 64ms.
* Some issues when fast-forwarding the gameplay
Other than that, things should work generally fairly well, both in shared and exclusive mode.
Because WASAPI is only available since Windows Vista, and because Mingw no longer supports Windows XP, the Windows releases will likely be split up into two separate versions. There will be a version (compiled with MSVC) that will work on Windows 98/2000/XP and up, and a separate version that will work from Windows Vista and up. This latter version will support WASAPI and other more advanced features only available since Vista.
Be on the lookout for further announcements related to bounties for the month of April soon!