-h,–help
Show command help
-o<FILE>
Output filename.
-p,–profile<n>
Target profile (MPEG4 audio object type, AOT)
2 MPEG-4 AAC LC (default)
5 MPEG-4 HE-AAC (SBR)
29 MPEG-4 HE-AAC v2 (SBR+PS)
23 MPEG-4 AAC LD
39 MPEG-4 AAC ELD
-b,–bitrate<n>
Target bitrate (for CBR)
-m,–bitrate-mode<n>
Bitrate configuration mode. Available VBR quality value depends on other parameters such as pro‐
file, sample rate, or number of channels.
0 CBR (default)
1-5 VBR (higher value -> higher bitrate)
-w,–bandwidth<n>
Frequency bandwidth (lowpass cut-off frequency) in Hz. Available on AAC LC only.
-a,–afterburner<n>
Configure afterburner mode. When enabled, quality is increased at the expense of additional com‐
putational workload.
0 Off
1 On (default)
-L,–lowdelay-sbr<n>
Configure SBR activity on AAC ELD.
-1 Use ELD SBR auto configuration
0 Disable SBR on ELD (default)
1 Enable SBR on ELD
-s,–sbr-ratio<n>
Controls activation of downsampled SBR.
0 Use lib default (default)
1 Use downsampled SBR (default for ELD+SBR)
2 Use dual-rate SBR (default for HE-AAC)
Dual-rate SBR is what is normally used for HE-AAC, where AAC is encoded at half the sample rate of
SBR, hence “dual rate”. On the other hand, downsampled SBR uses same sample rate for both of AAC
and SBR (single rate), therefore downsampled SBR typically consumes more bitrate.
Downsampled SBR is newly introduced feature in FDK encoder library version 3.4.12. When
libfdk-aac in the system doesn’t support this, dual-rate SBR will be used. When available,
dual-rate SBR is the default for HE-AAC and downsampled SBR is the default for ELD+SBR.
Note that downsampled HE-AAC is not so common as dual-rate one. When downsampled HE-AAC is se‐
lected, fdkaac is forced to choose explicit hierarchical SBR signaling, which (at least) iTunes
doesn’t accept.
-f,–transport-format<n>
Transport format. Tagging and gapless playback is only available on M4A. Streaming to stdout is
only available on others.
0 M4A (default)
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 the transport layer.
-G,–gapless-mode<n>
Method to declare amount of encoder delay (and padding) in M4A container. These values are manda‐
tory for proper gapless playback on player side.
0 iTunSMPB (default)
1 ISO standard (edts and sgpd)
2 Both
–include-sbr-delay
When specified, count SBR decoder delay in encoder delay.
This is not iTunes compatible and will lead to gapless playback issue on LC only decoder, but this
is the default behavior of FDK library.
Whether counting SBR decoder delay in encoder delay or not result in incompatibility in gapless
playback. You should pick which one will work for your favorite player.
However, it’s better not to choose SBR at all if you want gapless playback. LC doesn’t have such
issues.
-I,–ignorelength
Ignore length field of data chunk in input WAV file.
-S,–silent
Don’t print progress messages.
–moov-before-mdat
Place moov box before mdat box in M4A container. This option might be important for some hardware
players, that are known to refuse moov box placed after mdat box.
-R,–raw
Regard input as raw PCM.
–raw-channels<n>
Specify number of channels of raw input (default: 2)
–raw-rate<n>
Specify sample rate of raw input (default: 44100)
–raw-format<spec>
Specify sample format of raw input (default: “S16L”). Spec is as the following (case insensi‐
tive):
1stchar–typeofsampleS (igned) | U (nsigned) | F (loat)
2ndpart(indigits)
bits per channel
Lastchar–endianness(canbeomitted)L (ittle, default) | B (ig)
–title<string>
Set title tag.
–artist<string>
Set artist tag.
–album<string>
Set album tag.
–genre<string>
Set genre tag.
–date<string>
Set date tag.
–composer<string>
Set composer tag.
–grouping<string>
Set grouping tag.
–comment<string>
Set comment tag.
–album-artist<string>
Set album artist tag.
–track<number[/total]>
Set track tag, with or without number of total tracks.
–disk<number[/total]>
Set disk tag, with or without number of total discs.
–tempo<n>
Set tempo (BPM) tag.
–tag<fcc>:<value>
Set iTunes predefined tag with explicit fourcc key and value. See
<https://code.google.com/p/mp4v2/wiki/iTunesMetadata> for known predefined keys. You can omit
first char of fcc when it is the copyright sign.
–tag-from-file<fcc>:<filename>
Same as –tag, but set content of file as tag value.
–long-tag<name>:<value>
Set arbitrary tag as iTunes custom metadata. Stored in com.apple.iTunes field.
–tag-from-json<filename[?dot_notation]>
Read tags from JSON. By default, tags are assumed to be direct children of the root object in
JSON. Optionally you can specify arbitrary dot notation to locate the object containing tags.
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