Audacity freezes during Export to Nero AAC

Processor: Sandy Bridge i5-2520M
OS: Windows 7 Home Premium 64-bit
Audacity 2.0.0 (Unicode)
Nero AAC Encoder version (the zip says it’s though)
Source file: AC3 2-ch 384 kbps

So, the issue described in this thread still exists in the current version of Audacity. I’m using a similar command line

neroAacEnc.exe -ignorelength -if - -of "%f"

and Audacity freezes at exactly the 138-th second. Killing neroaacenc.exe restores the response of Audacity. Logs and command window output is exactly the same as in the thread I quoted.

Here’s some snapshots of CPU load (with 2 and 4 logical processors) during the freeze. CPU load seems to cycle, and they seem to add up to ~100 (equivalent to system’s 25%) altogether.

Limiting Audacity.exe to 1 logical processor works. But encoding takes ~4 or 5 times longer. Any ideas? Please let me know if you need more information.

As I understand it, Audacity is not (yet) multi-processor aware and most processing tasks are done in a single thread. Implementing full multiprocessor support would require a major rewrite of the Audacity code, but the developers priority has been on fixing bugs and releasing Audacity 2 rather than engaging in a major rewrite.
There is some discussion about this here:

I don’t know if the developers have any imminent plans in this area, but I can ask.

Pardon my ignorance, I don’t see how being not multiprocessor aware causes exporting to Nero AAC fail on default settings.

It appears that the Nero encoder (designed to be used with Nero) is expecting multiple threads when running on a multi-processor machine and stalls after 138 seconds if there is only a single thread. If Nero intended to support non-multi-threading applications, then it would probably be a bug in the encoder, but as Nero probably have no interest in supporting such then we’re probably stuck with the limitation until such time as Audacity supports multiple processors.