libfdk_aac


libfdk-aac AAC (Advanced Audio Coding) encoder wrapper.

The libfdk-aac library is based on the Fraunhofer FDK AAC code from the Android project.

Requires the presence of the libfdk-aac headers and library during configuration. You need to explicitly configure the build with --enable-libfdk-aac. The library is also incompatible with GPL, so if you allow the use of GPL, you should configure with --enable-gpl --enable-nonfree --enable-libfdk-aac.

This encoder is considered to produce output on par or worse at 128kbps to the but can often produce better sounding audio at identical or lower bitrates and has support for the AAC-HE profiles.

VBR encoding, enabled through the 'vbr' or 'flags +qscale' options, is experimental and only works with some combinations of parameters.

Support for encoding 7.1 audio is only available with libfdk-aac 0.1.3 or higher.

For more information see the fdk-aac project at .

The following options are mapped on the shared FFmpeg codec options.

'b'

Set bit rate in bits/s. If the bitrate is not explicitly specified, it is automatically set to a suitable value depending on the selected profile.

In case VBR mode is enabled the option is ignored.

'ar'

Set audio sampling rate (in Hz).

'channels'

Set the number of audio channels.

'flags +qscale'

Enable fixed quality, VBR (Variable Bit Rate) mode. Note that VBR is implicitly enabled when the 'vbr' value is positive.

'cutoff'

Set cutoff frequency. If not specified (or explicitly set to 0) it will use a value automatically computed by the library. Default value is 0.

'profile'

Set audio profile.

The following profiles are recognized:

'aac_low'

Low Complexity AAC (LC)

'aac_he'

High Efficiency AAC (HE-AAC)

'aac_he_v2'

High Efficiency AAC version 2 (HE-AACv2)

'aac_ld'

Low Delay AAC (LD)

'aac_eld'

Enhanced Low Delay AAC (ELD)

If not specified it is set to 'aac_low'.

The following are private options of the libfdk_aac encoder.

'afterburner'

Enable afterburner feature if set to 1, disabled if set to 0. This improves the quality but also the required processing power.

Default value is 1.

'eld_sbr'

Enable SBR (Spectral Band Replication) for ELD if set to 1, disabled if set to 0.

Default value is 0.

'signaling'

Set SBR/PS signaling style.

It can assume one of the following values:

'default'

choose signaling implicitly (explicit hierarchical by default, implicit if global header is disabled)

'implicit'

implicit backwards compatible signaling

'explicit_sbr'

explicit SBR, implicit PS signaling

'explicit_hierarchical'

explicit hierarchical signaling

Default value is 'default'.

'latm'

Output LATM/LOAS encapsulated data if set to 1, disabled if set to 0.

Default value is 0.

'header_period'

Set StreamMuxConfig and PCE repetition period (in frames) for sending in-band configuration buffers within LATM/LOAS transport layer.

Must be a 16-bits non-negative integer.

Default value is 0.

'vbr'

Set VBR mode, from 1 to 5. 1 is lowest quality (though still pretty good) and 5 is highest quality. A value of 0 will disable VBR, and CBR (Constant Bit Rate) is enabled.

Currently only the 'aac_low' profile supports VBR encoding.

VBR modes 1-5 correspond to roughly the following average bit rates:

'1'

32 kbps/channel

'2'

40 kbps/channel

'3'

48-56 kbps/channel

'4'

64 kbps/channel

'5'

about 80-96 kbps/channel

Default value is 0.