#Slow seek, but in sync
ffmpeg -i infile.mkv -vcodec mpeg4 -acodec aac -strict experimental -ar 48000 -ab 192k -qscale 1 -ss 0:53:46 -t 0:00:18 outfile.mp4

#Fast seek, but horribly out of sync
ffmpeg -ss 0:53:46 -i infile.mkv -vcodec mpeg4 -acodec aac -strict experimental -ar 48000 -ab 192k -qscale 1 -t 0:00:18 outfile.mp4