On Linux, the audio recording and video recording can be accomplished with a single command:

  ffmpeg -f x11grab -video_size [w]x[h] -r [framerate] -i $DISPLAY -f alsa -i default ...

Like the author, I've found that the x264 codec with the ultrafast preset does the best job of avoiding framedrops (which from what I've observed can be caused by either the CPU spending too long encoding or the disk spending too long writing data).