Freeware Advanced Audio Coder

FAAC is an LGPL-licensed, dependency-free AAC encoder and decoder suite with a resampler and MP4 muxer. It targets high-throughput media pipelines and constrained devices where footprint, speed, and quality all matter.

Key Features

• Codecs: MPEG-4 AAC-LC, HE-AAC v1 (SBR), and HE-AAC v2 (PS) encoding and decoding.
• Formats: 8 kHz to 96 kHz sample rates, mono up to 7.1 multichannel.
• Rate control: VBR, ABR, and CBR.
• Embedded-ready: No external dependencies; compile-time feature gating keeps binaries small.
• Libraries: libfaac (encoder), libfaad (decoder), libfaar (resampler), libfaam (MP4 muxer/demuxer).

Command-line Tools

• faac: Encodes WAV/PCM to AAC (ADTS or MP4/M4A) with automatic gapless metadata injection.
• faad: Decodes ADTS or MP4/M4A AAC to WAV/PCM, supporting downmixing and stdin/stdout piping.
• faar: Resamples WAV/PCM streams with adjustable quality tiers and optional PCM dithering.
• faam: Muxes, demuxes, and tags MP4/M4A/M4B containers in-place (including H.264/H.265 video tracks).

Important: The use of this software may require the payment of patent royalties. You need to consider this issue before you start building derivative works. We are not warranting or indemnifying you in any way for patent royalties! YOU ARE SOLELY RESPONSIBLE FOR YOUR OWN ACTIONS!

Usage

faac input.wav -o output.m4a          # encode PCM to AAC in MP4
faad output.m4a -o decoded.wav        # decode AAC to PCM
faad -i output.m4a                    # show stream information
faar -r 48000 in_96k.wav out_48k.wav  # resample to 48 kHz
faam -i output.aac -o output.m4a      # mux ADTS into MP4
faam tag output.m4a --title Song      # edit tags in place

Build

Install Meson and Ninja, then build and install the suite:

meson setup build
meson compile -C build
meson test -C build --print-errorlogs
meson install -C build

Build options

Option	Default	Description
decoder	true	Build libfaad and the faad frontend
decoder-dab	true	Digital Audio Broadcasting (960/120 frame length) support in libfaad
decoder-drc	true	Dynamic range control support in libfaad
decoder-ps	true	Parametric Stereo (HE-AAC v2) support in libfaad; needs decoder-sbr
decoder-sbr	true	Spectral Band Replication (HE-AAC v1) support in libfaad
encoder	true	Build libfaac and the faac frontend
encoder-drc	true	Dynamic range control metadata generation in libfaac (--drc)
encoder-ps	false	Enable HE-AAC v2 Parametric Stereo encoding; needs encoder-sbr
encoder-sbr	true	Spectral Band Replication (HE-AAC v1) support in libfaac; false builds an LC-only encoder
frontend	true	Build the command-line tools
frontend-static	false	Link the frontend executables to the static libraries
max-channels	8	Maximum number of channels (1-8)
muxer	true	Build the faam command-line tool (libfaam is always built)
muxer-chapters	true	libfaam: writing, updating and reading chapters
muxer-fragmented	true	libfaam: fragmented MP4 recording and demuxing
muxer-video	true	libfaam: H.264/H.265 video tracks
resampler	true	Build the faar command-line tool (libfaar is always built)
resampler-float	false	Use the float-only resampler engine for FPU-less targets; the default mixed build uses double at High quality
sbr-decimation	1	Encoder Spectral Band Replication analysis density (1 = full quality, up to 8 = faster)
stats	false	End-of-stream diagnostics on stderr (instrumentation only)

Library APIs

Applications can link the component libraries directly. Their public C APIs, build instructions, and usage details are documented here:

• FAAC encoder API
• FAAD decoder API
• FAAR resampler API
• FAAM MP4 muxer and demuxer API

Copyrights

FAAC, FAAD, FAAR and FAAM are free software, licensed under the GNU Lesser General Public License (LGPL), version 2.1 or later:

FAAC - Freeware Advanced Audio Coder
Copyright (C) 1999-2001, Menno Bakker
Copyright (C) 2002-2017, Krzysztof Nikiel
Copyright (C) 2004, Dan Villiom P. Christiansen
Copyright (C) 2005-2026, Fabian Greffrath
Copyright (C) 2026, Nils Schimmelmann

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.