Entering "libfaac" as the MP4 encoder on the Video Solution Pack admin page gets me the error.
"The selected MP4 codec was not found in ffmpeg. Try using aac or enable the desired codec."
This seems to be because of the grep here:
It relies on 6 periods before the encoder name. But those periods should/could be characters based on
V..... = Video
A..... = Audio
S..... = Subtitle
.F.... = Frame-level multithreading
..S... = Slice-level multithreading
...X.. = Codec is experimental
....B. = Supports draw_horiz_band
.....D = Supports direct rendering method 1
So my relevant line for libfaac is
A..... libfaac libfaac AAC (Advanced Audio Coding) (codec aac)