Fraunhofer FDK AAC

Fraunhofer FDK AAC

Developer(s)	Fraunhofer IIS
Release information
Initial release	{{{released}}}
Stable release	Encoder 3.4.12 [1] / Decoder 2.5.5 [2]
Preview release
Compatibility
Operating system	Android, Linux
Additional information
Use	Encoder
License	Very liberal (NOTICE), but somehow considered non-free [3]
Website	Offical web page

Current AAC encoders (most to least recommended)
1	Apple AAC M/W
2	FhG AAC (Winamp) W
3	Fraunhofer FDK AAC S/L/M/W
4	Nero AAC L/W
5	FFmpeg 3.0+ AAC encoder S/L/M/W
6	FAAC S/L/M/W
7	Libav (pre-3.0 FFmpeg) AAC encoder S/L/M/W
S Source code available; L Linux; M macOS; W Windows
List of AAC encoders

The Fraunhofer FDK AAC is a high-quality open-source AAC encoder library developed by Fraunhofer IIS. It was officially released for Android, but has been ported to other platforms.

The licensed Fraunhofer AAC codec included in Winamp (often called FhG AAC) is not the same as the FDK AAC codec. While they use the same same approach, they are developed by different teams, and target different platforms. The FDK library is built around fixed-point math and originally targeted mobile devices.

FDK AAC is considered a favorable alternative to the Nero AAC codec, which is no longer developed.

Afterburner

Afterburner is "a type of analysis by synthesis algorithm which increases the audio quality but also the required processing power." Fraunhofer recommends to always activate this feature.

Audio Object Types

The library supports the following MPEG-2/4 AOTs:

Object Type ID	Audio Object Type	Description
2	AAC-LC	"AAC Profile" MPEG-2 Low-complexity (LC) combined with MPEG-4 Perceptual Noise Substitution (PNS)
5	HE-AAC	AAC LC + SBR (Spectral Band Replication)
29	HE-AAC v2	AAC LC + SBR + PS (Parametric Stereo)
23	AAC-LD	"Low Delay Profile" used for real-time communication
39	AAC-ELD	Enhanced Low Delay
129	MPEG-2 AAC LC
132	MPEG-2 HE-AAC (SBR)
156	MPEG-2 HE-AAC v2 (SBR+PS)

Bitrate Modes

AACENC_BITRATEMODE	Bitrate	Comment
0	CBR @ AACENC_BITRATE
1	VBR, about 32 kbps/channel
2	VBR, about 40 kbps/channel
3	VBR, about 48-56 kbps/channel	Max for HE and HEv2
4	VBR, about 64 kbps/channel
5	VBR, about 80-96 kbps/channel
6		Fixed frame mode.
7		Superframe mode.
8		LD/ELD full bitreservoir for packet based transmission

Bandwidth

The default bandwidth (or low-pass filter cutoff) for each bitrate mode will be the minimum of the appropriate value in the tables below or half the sample rate. This can be overridden, but the maximum value is 20000 Hz. [4]

The fdk-aac parameter is AACENC_BANDWIDTH. The only front-end that currently allows this value to be changed is FFmpeg.

More information can be found in the official documentation, section 3.1 Bandwidth.

VBR Modes

AACENC_BITRATEMODE	Mono	Two or More Channels
1	13050 Hz
2	13050 Hz
3	14260 Hz
4	15500 Hz
5	Full range, no filter

CBR Mode

AOT/Sample Rates	Bitrate per channel	Mono	Two or More Channels
LC / Any	Below 12kbps	3700 Hz	5000 Hz
	12-20 kbps	5000 Hz	6400 Hz
	20-28 kbps	6900 Hz	9640 Hz
	28-40 kbps	9600 Hz	13050 Hz
	40-56 kbps	12060 Hz	14260 Hz
	56-72 kbps	13950 Hz	15500 Hz
	72-96 kpbs	14200 Hz	16120 Hz
	96kbps and above	17000 Hz
...
LD / 44100 Hz	56kbps	11000 Hz	12900 Hz
	64kbps	14400 Hz	15500 Hz
...

Sample Format

The FDK library is based on fixed-point math and only supports 16-bit integer PCM input.

Sample Rates

FDK library officially supports sample rates for input of 8000, 11025, 12000, 16000, 22050, 24000, 32000, 44100, 48000, 64000, 88200, and 96000 Hz.

See Issues/GetInvInt table limit if experiencing crashes with high sample rates and VBR.

Channel Layouts

Channels	Layout	Mode	Description
1	C	MODE_1	Mono
2	L+R	MODE_2	Stereo
3	C, L+R	MODE_1_2
4	C, L+R, Rear	MODE_1_2_1	fdkaac calls it "C L R Cs"
5	C, L+R, LS+RS	MODE_1_2_2
5.1	C, L+R, LS+RS, LFE	MODE_1_2_2_1
7.1	C, LC+RC, L+R, LS+RS, LFE	MODE_1_2_2_2_1 MODE_7_1_FRONT_CENTER
7.1 (Rear)	C, L+R, LS+RS, Lrear+Rrear, LFE	MODE_7_1_REAR_SURROUND

Issues

GetInvInt table limit

As of FDK version 3.4.12, not all combinations of audio object types, bitrate modes, channel layouts, and sample rates can be used together, due to a limited table of pre-computed values used by the encoder. For example, using 96kHz stereo input with the AAC-LC audio object type and bitrate mode 5 (VBR 80-96kbps/channel) will result in catastrophic failure. [5]. A recent (August 2014) patch to libfdk-aac fixes most of the previously unsupported combinations [6], and is expected to be included in the next official version of the FDK AAC library.

Recommended Sampling Rate and Bitrate Combinations

This table is from the documentation included in the FDK library source code. (PDF section 2.12 or source code: [7])

The following table provides an overview of recommended encoder configuration parameters which [Fraunhofer] determined by virtue of numerous listening tests.

Audio Object Type	Bit Rate Range [bit/s]	Supported Sampling Rates [kHz]	Recommended Sampling Rate [kHz]	Number of Channels
[29] HE-AAC v2 (AAC LC + SBR + PS)	8000 - 11999	22.05, 24.00	24.00	2
	12000 - 17999	32.00	32.00	2
	18000 - 39999	32.00, 44.10, 48.00	44.10	2
	40000 - 56000	32.00, 44.10, 48.00	48.00	2
[5] HE-AAC (AAC LC + SBR)	8000 - 11999	22.05, 24.00	24.00	1
	12000 - 17999	32.00	32.00	1
	18000 - 39999	32.00, 44.10, 48.00	44.10	1
	40000 - 56000	32.00, 44.10, 48.00	48.00	1
	16000 - 27999	32.00, 44.10, 48.00	32.00	2
	28000 - 63999	32.00, 44.10, 48.00	44.10	2
	64000 - 128000	32.00, 44.10, 48.00	48.00	2
[5] HE-AAC (AAC LC + SBR)	64000 - 69999	32.00, 44.10, 48.00	32.00	5, 5.1
	70000 - 159999	32.00, 44.10, 48.00	44.10	5, 5.1
	160000 - 245999	32.00, 44.10, 48.00	48.00	5
	160000 - 265999	32.00, 44.10, 48.00	48.00	5.1
[2] AAC LC	8000 - 15999	11.025, 12.00, 16.00	12.00	1
	16000 - 23999	16.00	16.00	1
	24000 - 31999	16.00, 22.05, 24.00	24.00	1
	32000 - 55999	32.00	32.00	1
	56000 - 160000	32.00, 44.10, 48.00	44.10	1
	160001 - 288000	48.00	48.00	1
[2] AAC LC	16000 - 23999	11.025, 12.00, 16.00	12.00	2
	24000 - 31999	16.00	16.00	2
	32000 - 39999	16.00, 22.05, 24.00	22.05	2
	40000 - 95999	32.00	32.00	2
	96000 - 111999	32.00, 44.10, 48.00	32.00	2
	112000 - 320001	32.00, 44.10, 48.00	44.10	2
	320002 - 576000	48.00	48.00	2
[2] AAC LC	160000 - 239999	32.00	32.00	5, 5.1
	240000 - 279999	32.00, 44.10, 48.00	32.00	5, 5.1
	280000 - 800000	32.00, 44.10, 48.00	44.10	5, 5.1

[lib]fdk-aac

The opencore-amr project maintains a source code distribution of the Fraunhofer library as fdk-aac, often packaged as libfdk-aac. It is distributed in a binary form in Debian (and Debian derivatives like Ubuntu) as libfdk-aac0.

The latest libfdk-aac release is 0.1.3 (2013-11-25), based on FDK version 3.4.12. [8].

aac-enc

fdk-aac includes a very, very basic command-line interface encoding utility, called aac-enc, that can encode to AAC from WAV.

Usage:

aac-enc [-r bitrate] [-t aot] [-a afterburner] [-s sbr] [-v vbr] in.wav out.aac

-r <bitrate>

Bitrate in bits per seconds (for CBR). Default is 64000.

-t <aot>

The Audio Object Type. Default is 2 (AAC-LC).

-a <0,1>

Enable Afterburner. 0=Disabled, 1=Enabled (recommended). Default is 1.

-s <-1,0,1>

Spectral Band Replication (ELD AOT only). -1=Use ELD SBR auto configurator (default,recommended), 0=Disabled, 1=Enabled. Default is -1.

-v <0-5>

Bitrate mode. Only 0-5 used. 0=CBR @ value given in -r. Default is 0.

fdkaac

fdkaac

Developer(s)	nu774
Release information
Initial release	{{{released}}}
Stable release	0.5.3
Preview release
Compatibility
Operating system	Linux, Windows, others
Additional information
Use	Encoder
License	Zlib
Website	github page for fdkaac

fdkaac is a command-line interface encoding and metadata utility. It uses libfdk-aac.

Example:

# Convert a FLAC file to m4a using fdkaac configured for AAC-LC at about 50kbps/channel (100kbps for stereo).
flac -s -d -c song.flac | fdkaac --ignorelength -profile 2 --bitrate-mode 3 -o song.m4a -

Usage:

fdkaac [options] input_file

-p, --profile <n>

The Audio Object Type.

-b, --bitrate <n>

Bitrate in bits per seconds (for CBR)

-m, --bitrate-mode <n>

Bitrate mode. Only 0-5 used. 0=CBR.

-w, --bandwidth <n>

Frequency bandwidth in Hz (AAC LC only)

-a, --afterburner <n>

Enable Afterburner. 0=Disabled, 1=Enabled (recommended). Default is 1.

-L, --lowdelay-sbr <-1,0,1>

Configure SBR activity on AAC ELD

-1	Use ELD SBR auto configurator
0	Disable SBR on ELD (default)
1	Enable SBR on ELD

-s, --sbr-ratio <0,1,2>

Controls activation of downsampled SBR

0	Use lib default (default)
1	Downsampled SBR (default for ELD+SBR)
2	Dual-rate SBR (default for HE-AAC)

-f, --transport-format <n>

Transport format

0	RAW (default, muxed into M4A)
1	ADIF
2	ADTS
6	LATM MCP=1
7	LATM MCP=0
10	LOAS/LATM (LATM within LOAS)

-C, --adts-crc-check

Add CRC protection on ADTS header

-h, --header-period <n>

StreamMuxConfig/PCE repetition period in transport layer

-o <filename>

Output filename

-G, --gapless-mode <n>

Encoder delay signaling for gapless playback

0	iTunSMPB (default)
1	ISO standard (edts + sgpd)
2	Both

--include-sbr-delay

Count SBR decoder delay in encoder delay. This is not iTunes compatible, but is default behavior of FDK library.

-I, --ignorelength

Ignore length of WAV header

-S, --silent

Don't print progress messages

--moov-before-mdat

Place moov box before mdat box on m4a output

Options for raw (headerless) input:

-R, --raw

Treat input as raw (by default WAV is assumed)

--raw-channels <n>

Number of channels (default: 2)

--raw-rate <n>

Sample rate (default: 44100)

--raw-format <spec>

Sample format, default is "S16L". Spec is as follows:

1st char	S(igned), U(nsigned), or F(loat)
2nd part	bits per channel
Last char	L(ittle) or B(ig)

Last char can be omitted, in which case L is assumed. Spec is case insensitive, therefore "u16b" is same as "U16B".

Up to 32-bit integer or 64-bit floating point format is supported as input. The FDK library, however, is implemented based on fixed point math and onlysupports 16-bit integer PCM. Therefore, be wary of clipping. You might want to dither/noise shape beforehand when your input has higher resolution.

Tagging options:

--tag <fcc>

<value>: Set iTunes predefined tag with four char code. See iTunes Metadata.

--tag-from-file <fcc>:<filename>

Same as above, but value is read from file.

--long-tag <name>:<value>

Set arbitrary tag as iTunes custom metadata.

--tag-from-json <filename[?dot_notation]>

Read tags from JSON. By default, tags are assumed to be direct children of the root object(dictionary). Optionally, position of the dictionary that contains tags can be specified with dotted notation.

Option/Usage	MP4 Block Modified	Comment
--title <string>	©nam
--artist <string>	©ART
--album <string>	©alb
--genre <string>	©gen	Appears to always store the string the "user-defined" ©gen even if there is an ID3 genre id that could be used with the gnre block.
--date <string>	©day	YYYY[-MM[-DD]] format
--composer <string>	©wrt
--grouping <string>	©grp
--comment <string>	©cmt
--album-artist <string>	aART
--track <number[/total]>	trkn	Block stores both track and totaltracks in one binary value
--disk <number[/total]>	disk	Block stores both disc and totaldiscs in one binary value
--tempo <n>	tmpo	Beats per minute, stored as a 16-bit integer

• Source code
• Ubuntu PPA

FFmpeg

libfdk-aac can be used with FFmpeg, but requires a custom build of FFmpeg. FFmpeg provides significant documentation for using libfdk_aac in the FFmpeg wiki.

CBR mode:

ffmpeg -i <input> -c:a libfdk_aac -b:a 128k <output>

VBR mode:

ffmpeg -i <input> -c:a libfdk_aac -vbr 3 <output>

-afterburner

Enable Afterburner. 0=Disabled, 1=Enabled (recommended). Default is 1.

-profile:a

The Audio Object Type. Value is one of LC, HE-AAC, HE-AACv2, LD, or ELD. Default is LC.

-b:a

CBR bitrate

-vbr

Values 1-5. See Bitrate mode.

--cutoff

The low-pass filter cut-off in Hz. See Bandwidth for default values. FFmpeg maximum value is 20000.

Libav/avconv

libfdk-aac can be used with Libav's avconv, but requires a custom build of avconv with "--enable-libfdk-aac" passed to configure.

CBR mode:

avconv -i <input> -c:a libfdk_aac -b:a <bitrate> -afterburner 1 <output>

VBR mode:

avconv -i <input> -c:a libfdk_aac -flags +qscale -global_quality [1-5] -afterburner 1 <output>

-afterburner

See afterburner.

-global_quality

Values 1-5. See Bitrate mode.

Links

• Release information HydrogenAudio forums
• FDK in Android source code
• fdk-aac source code