https://bugs.winehq.org/show_bug.cgi?id=41101
--- Comment #27 from Daniel Perelman dap56@cornell.edu ---
Sorry, it sounds like you tried what I did. I did install pretty much every i386 gstreamer package I could get from Debian/Debian-multimedia, so I'm not sure which ones were actually required.
The only I can think of would be gst-libav but I already have that installed.
Here's the list of all of the i386 gstreamer packages I have installed (although this may not translate directly to Arch): gstreamer1.0-fluendo-mp3:i386 gstreamer1.0-libav:i386 gstreamer1.0-nice:i386 gstreamer1.0-plugins-base:i386 gstreamer1.0-plugins-good:i386 gstreamer1.0-pulseaudio:i386 gstreamer1.0-tools:i386 gstreamer1.0-x:i386 libgstreamer1.0-0:i386 libgstreamer-plugins-base1.0-0:i386