My team is tasked with building a full screen, kiosk-style application for playing back media files. Initially we need to support WMV / MP4 as well as some images in full 1080p, although down the line we will need to extend this to cover other formats (different videos formats as well as display of HTML, SWF, etc).

The application also contains a decent chunk of business logic relating to scheduling, logging, performance monitoring as well as network code to talk to a central server through web services (or maybe TCP) and potentially act as a server itself.

For our WMV / MP4 video playback, hardware acceleration will be a massive bonus. The targetted hardware has weak CPUs but strong graphics cards.

Here's the kicker: we're a .NET shop (our existing application is a WinForms smart client) and extremely experienced and productive in C# and the .NET stack. The app will initially be targetting Windows Embedded (.NET 3.0), *but* we will quickly need a Linux version as well. Between us we have some C/C++ experience and some Linux experience but we do not anticipate good productivity on that platform.

So I am soliciting recommendations specfically on the following points:

1. Video. On Windows we have seen good success using DirectShow.NET. On capable hardware, the WPF MediaElement also seems to perform well. What should we be using on Linux? libavcodec seems like a common choice. Is it hardware accelerated on NVidia graphics cards on Linux? What other options do we have on Linux? Is there something cross-platform that I could consider?
2. Stack.
a) Ideally we could write the whole thing in .NET and then run under Mono on Linux. The video playback and presumably some other components (like performance monitoring) would not be supported on Mono. I guess we could rewrite these elements in, say, C++; but I'm guessing that most stuff on the business logic side would work.
b) Maybe it's better to forfeit our up-front productivity on the Windows version for something that's cross platform out of the gate. What about Java? Do we have different options when it comes to video there? How about another framework? Something like QT? Can anyone else suggest something cross platform that would be relevant?

Broadly speaking, given the requirements, what would *you* use?

I appreciate any anwsers you might have.