Fraunhofer FDK AAC

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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.

Not all combinations of audio object types, bitrate modes, channel layouts, and sample rates can be used together. For example, using 96kHz stereo input with the AAC-LC audio object type and bitrate mode 5 (VBR 80-96kHz/channel) will result in catastrophic failure. [5]. See Recommended Sampling Rate and Bitrate Combinations for recommended combinations.

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

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: [6])

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. [7].

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


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

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