Otherwise GTA San Andreas runs into it and crashes. This stub let's it work again.
a workaround is to disable wmvcore in winecfg...
---
 dlls/wmvcore/wmvcore.spec   |    2 +-
 dlls/wmvcore/wmvcore_main.c |    8 ++++++++
 2 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/dlls/wmvcore/wmvcore.spec b/dlls/wmvcore/wmvcore.spec
index 1c6cb1f..e0fa2e9 100644
--- a/dlls/wmvcore/wmvcore.spec
+++ b/dlls/wmvcore/wmvcore.spec
@@ -11,7 +11,7 @@
 @ stub WMCreateProfileManager
 @ stub WMCreateReader
 @ stub WMCreateReaderPriv
-@ stub WMCreateSyncReader
+@ stdcall WMCreateSyncReader(ptr long ptr)
 @ stub WMCreateWriter
 @ stub WMCreateWriterFileSink
 @ stub WMCreateWriterNetworkSink
diff --git a/dlls/wmvcore/wmvcore_main.c b/dlls/wmvcore/wmvcore_main.c
index 096328b..5fce972 100644
--- a/dlls/wmvcore/wmvcore_main.c
+++ b/dlls/wmvcore/wmvcore_main.c
@@ -22,6 +22,7 @@
 
 #include "windef.h"
 #include "winbase.h"
+#include "objbase.h"
 #include "wine/debug.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(wmvcore);
@@ -43,3 +44,10 @@ BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
 
     return TRUE;
 }
+
+HRESULT WINAPI WMCreateSyncReader(IUnknown *pcert, DWORD rights,
+                                  IUnknown /* FIXME: IWMSyncReader */ **syncreader)
+{
+    FIXME("(%p, %x, %p): stub\n", pcert, rights, syncreader);
+    return E_NOTIMPL;
+}