[FFmpeg-user] FFmpeg CPU usage

[Pete]

I have a huge number of videos to transcode. The quality of the videos vary 
from low to medium. DVD quality is probably the highest quality. I have ffmpeg 
and libx264 compiled with pthreads and I use -threads 0 in my call to ffmpeg 
but I'm still not seeing 100% usage on all the cores. I need to maximize cpu 
usage since I'm not trying to transcode videos for a month straight. 

Here is the ffmpeg call I'm using:
ffmpeg -y -i "$i" -c:v libx264 -preset fast -b:v "$VID_BIT" -threads 0 -c:a 
libfdk_aac -b:a "$AUD_BIT" -f mp4 /"$OUT_DIR"/"$MD5"

Could the libfdk_aac codec be the issue? I couldn't find anything online that 
explicitly stated whether or not this codec supports threading. I really hope 
it does since I need the audio to be able to stream in a browser and aac works 
very well for that purpose. 

Thanks,
Pete