Audio 24-bit libfdk_aac with ffmpeg

I would like to ask why ffmpeg & # 39; s libfdk_aac the encoder is automatically reducing the bit depth of my audio when encoding and I want to know how to stop it.

My coding is as such (all the data is there, except the metadata and file paths):

ffmpeg -i "/Path/To/Input.flac" -c: a libfdk_aac -b: a 192k -ar 48000 -map_metadata -1 -metadata title = "Title" -metadata artist = "Artist" -metadata date = "Date "" /Path/To/Output.m4a "
ffmpeg version 4.1 Copyright (c) 2000-2018 the developers of FFmpeg
Built with Apple LLVM version 10.0.0 (clang-1000.10.44.4)
configuration --prefix = / usr / local / Cellar / ffmpeg / 4.1 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc = clang - host- cflags = --host-ldflags = --enable-ffplay --enable-gpl --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx - enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-opencl --enable-videotoolbox --enable -no free
libavutil 56. 22.100 / 56. 22,100
libavcodec 58. 35,100 / 58. 35,100
libavformat 58. 20.100 / 58. 20,100
Libavdevice 58. 5.100 / 58. 5.100
libavfilter 7. 40.101 / 7. 40.101
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 3.100 / 5. 3.100
libswresample 3. 3.100 / 3. 3.100
libpostproc 55. 3.100 / 55. 3.100
Entry # 0, flac, from & # 39; /Path/To/Input.flac&#39 ;:
Duration: 00: 31: 31.71, start: 0.000000, bit rate: 4721 kb / s
Transmission # 0: 0: Audio: flac, 192000 Hz, stereo, s32 (24 bits)
Mapping the current:
Transmission # 0: 0 -> # 0: 0 (flac (native) -> aac (libfdk_aac))
press [q] to stop, [?] for help
Output # 0, ipod, to & # 39; /Path/To/Output.m4a&#39 ;:
Metadata:
title: title
artist: artist
date: date
encoder: lavf58.20.100
Transmission # 0: 0: Audio: aac (libfdk_aac) (mp4a / 0x6134706D), 48000 Hz, stereo, s16, 192 kb / s
Metadata:
Encoder: Lavc58.35.100 libfdk_aac
[NULL @ 0x7fb747801000] sample / table number does not match in adjacent boxes
size = 44686kB time = 00: 31: 31.71 bitrate = 193.5kbits / s speed = 22.2x
video: 0kB audio: 44338kB subtitle: 0kB other transmissions: 0kB global headings: 0kB muxing overload: 0.784360%

There are no problems with encoding … (I simply encode AAC, set the bitrate to 192 kbps and decrease the sample to 48000 kHz) except that, for some reason, the bit depth is reduced to 16 bits when it is encoded from a 24-bit source. I know that the libfdk_aac the encoder is compatible with 24 bits, but for some reason, the encoder is automatically reduced to sample. I tried to force 24 bit, with -sample_fmt s32 but that came back with this error:

[libfdk_aac @ 0x7fc58100b200]    The specified sample format s32 is not valid or is not compatible
Failed to initialize the output stream 0: 0: error when opening the encoder for the output stream # 0: 0, perhaps incorrect parameters such as bit rate, speed, width or height
The conversion failed!

If anyone knows, I would greatly appreciate an answer.