Fraunhofer FDK AAC
| Developer(s) | Fraunhofer IIS |
| Release information | |
|---|---|
| Stable release | |
| Compatibility | |
| Operating system | Android, Linux |
| Additional information | |
| Use | Encoder |
| License | Very liberal (NOTICE), but somehow considered non-free [1] |
| Website | Offical web page |
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.
MPEG-4 Audio Object Types
The library supports the following MPEG-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 |
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.
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 |
[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 release is 0.1.3 (2013-11-25) [2].
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
| Developer(s) | nu774 |
| Release information | |
|---|---|
| Stable release | 0.5.3 |
| Compatibility | |
| Operating system | Linux, Windows, others |
| Additional information | |
| Use | Encoder |
| License | Zlib |
| Website | github page for fdkaac |
fdkaac is a command-line interface encoding utility front-end to libfdk-aac.
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".
Tagging options:
- --title <string>
- --artist <string>
- --album <string>
- --genre <string>
- --date <string>
- --composer <string>
- --grouping <string>
- --comment <string>
- --album-artist <string>
- --track <number[/total]>
- --disk <number[/total]>
- --tempo <n>
- --tag <fcc>
- <value>: Set iTunes predefined tag with four char code.
- --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.
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>
- -vbr
- Values 1-5. See Bitrate mode.
avconv
libfdk-aac can be used with 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:
aconv -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.