This file contains information about the implementation of the multimedia layer of Wine.
The implementation can be found in the dlls/winmm/ directory (and in many of its subdirectories), but also in dlls/msacm/ (for the audio compression/decompression manager) and dlls/msvideo/ (for the video compression/decompression manager).
The multimedia stuff is split into 3 layers. The low level (device drivers), mid level (MCI commands) and high level abstraction layers. The low level layer has also some helper DLLs (like the MSACM/MSACM32 and MSVIDEO/MSVFW32 pairs).
All of those components are defined as DLLs (one by one).
The low level layer may depend on current hardware and OS services (like OSS on Unix). It provides the core of playback/record using fine grain objects (audio/midi streams...).
Mid level (MCI) and high level layers must be written independently from the hardware and OS services.
MCI level provides some coarser grain operations (like playing a Midi file, or playing a video stream).