I am using Pipelight in a virtual machine (under virtualbox) running Linux Mint 17 Cinnamon to view movies in a German Streaming portal (maxdome.de).

It works fine except that the audio lags behind the video by about one second.

This occurs 100% of the time, and I tried the following things without any positive (or negative) effects:

1) Restarted pulse audio with
2) tried pipelight in both windowless and windowed mode by copying /usr/share/pipelight/configs/pipelight-silverlight5.1 to ~/.config and editing the relevant lines.
3) Increased RAM of the vm to up to 4GB and made sure firefox was the only running application. (And the streaming site the only open tab) to rule out memory issues
4) ran to play with settings here but only had "pulseaudio" to choose from
5) reduced default-fragment-size-msec to 5 in /etc/pulse/daemon.conf

I can rule out slow internet connection because this works fine in a virtual windows xp install (which I'd obviously like to stop using)

What else could I try to get this working?

I am reluctant to install pipelight into my main system (I like to keep it clean from non-repository software), but would consider putting a distro only for that onto another partition if anyone thinks that the virtualization is a problem...

it will be slow on a VM
try a real install to the drive

Hmm, ok... I guess I'll take a shot at that maybe this coming weekend. Need to get around to actually installing the test system on another partition for that purpose. Although what bugs me about this approach is that on Windows XP in runs just fine, even in a VM... It would be a lot more convenient not to boot into another system whenever I want to use Pipelight...

Ok, tried a real install of mint 17 cinnamon. Works perfectly, no lagging at all.
Just to rule out that it was related to the DE I also tried installing cinnamon into a vm, but it was even worse than with MATE.
So I guess I'll have to live with the rebooting...

video will use the 3d card to uncompress it
however in a VM the 3d card is VIRTUAL and uses openGL to "simulate" the card
hence it is a bit slower

I see. But this begs the question whether the hardware representation you get when choosing "windows guest system" in the virtual box configuration while creating the machine does a better job at simulating the card than the one you get when installing a linux guest system or if it's the actual OS (Windows) that can handle the "slower card" better...