Mick Hardy
The new GPU enabled rendering engine "Magix AVC/AAC MP4" with an NVENC enabled template fails when using more than two instances.

Vegas throws an error, “A component failed to initialise".

This happens without TandemVids so it's a Vegas issue and isn't something we can fix.

I think we're stuck with two instances if we want to make use of the new speed improvements.

Six instances works slowly but without failing if you set the first two to use the NVENC encoder and the rest to use the normal encoder. This was really slow like 23 minutes per instance and the two set to use the GPU were only using it sporadically so they initially took way longer than the others and didn’t kick into gear until all other renders had completed. The first 50% for the GPU renderers was 22 minutes and the last 50% was 1 minute after the others completed.

I tried setting the last four to use a completely different rendering engine, “Sony AVC/MVC” and it was a bit faster, 15 minutes instead of 25 minutes.

With three instances, two using NVENC and one using Sony AVC, two completed in five minutes and the non GPU one in seven.

With two instances using NVENC, both completed in three minutes thirty.

All tests included photos and were reading from the same SD card, which was probably cached by Windows.

Vegas 16 is due out shortly but I can’t see it changing things.

Mick Hardy
After a lot of research, I'm led to believe this is due to artificial limitations imposed by nVidia on their Geforce line of graphics cards. It is not a Vegas limitation as originally assumed. Even the latest gaming cards, Geforce 1070 and 1080 only support two concurrent NVENC sessions.

There are no such limits on the Intel GPUs built into many of the Intel CPUs. You can use the Intel QSV encoder across unlimited instances. In my testing using the Intel QSV encoder, four concurrent instances completed in six minutes thirty. Five instances completed in eight minutes.

To use the NVENC encoder across more than two concurrent instances, you'll need a GPU with unrestricted concurrent sessions as per this nVidia support matrix.

I haven't tested it but I think the NVIDIA Quadro P2000 available in Australia for $600AUD will resolve the issue.