Audacity 2.1.2 vs 2.0.5 (FFMpeg speed)

Audacity 2.0.5 + FFMpeg 0.6.2 (avformat-52.dll) is four times more fast, opening AC3 and Multiple Export (WAV) that Audacity 2.1.2 + FFMpeg 2.2.2 (avformat-55.dll).
Maybe due avformat-55.dll is much bigger that avformat-52.dll.

I do this process opening AC3 files 640kbps, then exporting WAV tracks and at last, encoding to AC3 384kbps with WAV to AC3 Encoder.

Is not a bug, but I will continue using old version 2.0.5, due to this performance issue.

Sorry if my english is bad.

You can use the standard WAV exporter to export multi-channel WAV.

Are you editing these files while they are in Audacity? Re-encoding a lossy format like AC3 always degrades the file, even if you increase the bit rate.