Hi,
I'm also weirded out with the lack of performance under some circunstances, namely multi-screen output.
The system in use is an AMD X3 (2.1Ghz, triple core A6) processor, fast-ish RAM (4GB PC1600 DDR3 low latency) and AMD 65xx family GPU(s)/APU.
When used with just 1 screen output, framerates (360p on h264 flv's scaled to fit a screen area aprox. 720x400) are acceptable (say 20+fps). Plus animations etc on the rest of the screen (sometimes 1 of them can be simple SWF, but really not much going on).
Still, not superfluid, but OK when all the content is played in one output (even at 2560x1440).
The other output, when played by itself, also acceptable.
Checking CPU utilization and GPU (using benchmarking software, etc), it shows that the 3 CPU's peak at aprox. 63% of fairly constant usage and GPU 1 is at 0% usage and GPU 2 is at 37% MAX (about 10% average) usage.
So plenty of CPU still to spare and almost no GPU used.
When I output through both GPU's at the same time, the performance goes downhill tremendously, more than with the 3.x line of players, to the point of just one 360p video (+animations etc) goes to about 12fps.
What's worse is that CPU GPU utilization remain the same, very low, with near 50% of CPU unused, one GPU not used at all and near 80% of the other still available.
I thought of memory bandwith/PCIe bottlenecks, but the GPU's don't share PCIe, one has 1GB of local RAM, the other shares 256MB with the motherboard (but only ouputs a 720p screen and is recent gen APU), etc.
In other words, I think AIR (latest version, win7x64, been trying AMD beta-and-what-not driver releases for 6 months) is not using all the "CPU/GPU" it could. Not sure this is something particular to digital signage, and I guess you're already setting all AIR flags to maximun performance on the players, but well, this is what's happening to my systems.
If you wanna build experimental players with say GPU acceleration disabled on AIR or something to see if that improves anything, I'll be happy to try them.
I've been trying to profile what's going on but as far as I can tell the AIR platform is being very little agressive when it comes to using resources available even when it needs them.
Perhaps the stage is getting set to too few fps somehow?