Encoding formats¶
Encoders are used to define formats into which raw sources should be encoded by
an output. Syntax for encoder is: %encoder(parameters...)
or, if you use
default parameters, %encoder
.
Please note that not all encoding formats are available at all time. Most of them require optional dependencies. If a format is not available, you should see an error like this:
Error 12: Unsupported encoder: %sine().
You must be missing an optional dependency.
In particular, due to limitations with static linking on windows, only the
%ffmpeg
encoder is available with our windows build. However, this encoder provides
a lot of codecs and formats, and it is quite likely that it can provide what you need.
Formats determine the stream content¶
In most liquidsoap scripts, the encoding format determines what kind of data is streamed.
The type of an encoding format depends on its parameter.
For example, %mp3
has type format(audio=2,video=0,midi=0)
but %mp3(mono)
has type format(audio=1,video=0,midi=0)
.
The type of an output like output.icecast
or output.file
is something like
(...,format('a),...,source('a))->source('a)
.
This means that your source will have to have the same type as your format.
For example if you write
output.file(%mp3,"/tmp/foo.mp3",playlist("~/audio"))
then the playlist source will have to stream stereo audio. Thus it will reject mono and video files.
Liquidsoap provides operators that can be used to convert sources
into a format acceptable for a given encoder. For instance, the mean
operator transforms any audio source into a mono source and the audio_to_stereo
operator transforms any audio source into a stereo source.
List of formats and their syntax¶
All parameters are optional, and the parenthesis are not needed
when no parameter is passed. In the following default values
are shown.
As a special case, the keywords mono
and stereo
can be used to indicate
the number of channels (whether is is passed as an integer or a boolean).
MP3¶
Mp3 encoder comes in 3 flavors:
%mp3
or%mp3.cbr
: Constant bitrate encoding%mp3.vbr
: Variable bitrate, quality-based encoding.%mp3.abr
: Average bitrate based encoding.
Parameters common to each flavor are:
stereo=true/false
,mono=true/false
: Encode stereo or mono data (default:stereo
).stereo_mode
: One of:"stereo"
,"joint_stereo"
or"default"
(default:"default"
). Default means that the underlying library (libmp3lame
) will pick the stereo mode based on compression ration and input channels.samplerate=44100
: Encoded data samplerate (default:44100
)internal_quality=2
: Lame algorithms internal quality. A value between0
and9
,0
being highest quality and9
the worst (default:2
).id3v2=true
: Add anid3v2
tag to encoded data (default:false
). This option is only valid if liquidsoap has been compiled with taglib support.
Parameters for %mp3
are:
bitrate
: Encoded data fixed bitrate
Parameters for %mp3.vbr
are:
quality
: Quality of encoded data; ranges from0
(highest quality) to9
(worst quality).
Parameters for %mp3.abr
are:
bitrate
: Average bitratemin_bitrate
: Minimum bitratemax_bitrate
: Maximum bitratehard_min
: Enforce minimal bitrate
Examples:
- Constant
128
kbps bitrate encoding:%mp3(bitrate=128)
- Variable bitrate with quality
6
and samplerate of22050
Hz:%mp3.vbr(quality=7,samplerate=22050)
- Average bitrate with mean of
128
kbps, maximum bitrate192
kbps andid3v2
tags:%mp3.abr(bitrate=128,max_bitrate=192,id3v2=true)
Optionally, liquidsoap can insert a message within mp3 data. You can set its value using the msg
parameter.
Setting it to ""
disables this feature. This is its default value.
Shine¶
Shine is the fixed-point mp3 encoder. It is useful on architectures without a FPU, such as ARM.
It is named %shine
or %mp3.fxp
and its parameters are:
%shine(channels=2,samplerate=44100,bitrate=128)
WAV¶
%wav(stereo=true, channels=2, samplesize=16, header=true, duration=10.)
If header
is false
, the encoder outputs raw PCM. duration
is optional
and is used to set the WAV length header.
Because Liquidsoap encodes a possibly infinite stream, there is no way to know in advance the duration of encoded data. Since WAV header has to be written first, by default its length is set to the maximum possible value. If you know the expected duration of the encoded data and you actually care about the WAV length header then you should use this parameter.
FFmpeg¶
See detailed ffmpeg encoders article.
Ogg¶
The following formats can be put together in an Ogg container.
The syntax for doing so is %ogg(x,y,z)
but it is also
possible to just write %vorbis(...)
, for example, instead
of %ogg(%vorbis(...))
.
All ogg encoders have a bytes_per_page
parameter, which can be used to
try to limit ogg logical pages size. For instance:
# Try to limit vorbis pages size to 1024 bytes
%vorbis(bytes_per_page=1024)
Vorbis¶
# Variable bitrate
%vorbis(samplerate=44100, channels=2, quality=0.3)
% Average bitrate
%vorbis.abr(samplerate=44100, channels=2, bitrate=128, max_bitrate=192, min_bitrate=64)
# Constant bitrate
%vorbis.cbr(samplerate=44100, channels=2, bitrate=128)
Quality ranges from -0.2 to 1, but quality -0.2 is only available with the aotuv implementation of libvorbis.
Opus¶
Opus is a lossy audio compression made especially suitable for interactive real-time applications over the Internet. Liquidsoap supports Opus data encapsulated into Ogg streams.
The encoder is named %opus
and its parameters are as follows. Please refer
to the Opus documentation for information about
their meanings and values.
vbr
: one of"none"
,"constrained"
or"unconstrained"
application
: One of"audio"
,"voip"
or"restricted_lowdelay"
complexity
: Integer value between0
and10
.max_bandwidth
: One of"narrow_band"
,"medium_band"
,"wide_band"
,"super_wide_band"
or"full_band"
samplerate
: input samplerate. Must be one of:8000
,12000
,16000
,24000
or48000
frame_size
: encoding frame size, in milliseconds. Must be one of:2.5
,5.
,10.
,20.
,40.
or60.
.bitrate
: encoding bitrate, inkbps
. Must be a value between5
and512
. You can also set it to"auto"
.channels
: currently, only1
or2
channels are allowed.mono
,stereo
: equivalent tochannels=1
andchannels=2
.signal
: one of"voice"
or"music"
Theora¶
%theora(quality=40,width=640,height=480,
picture_width=255,picture_height=255,
picture_x=0, picture_y=0,
aspect_numerator=1, aspect_denominator=1,
keyframe_frequency=64, vp3_compatible=false,
soft_target=false, buffer_delay=5,
speed=0)
You can also pass bitrate=x
explicitly instead of a quality.
The default dimensions are liquidsoap’s default,
from the settings frame.video.height/width
.
Speex¶
%speex(stereo=false, samplerate=44100, quality=7,
mode=wideband, # One of: wideband|narrowband|ultra-wideband
frames_per_packet=1,
complexity=5)
You can also control quality using abr=x
or vbr=y
.
Flac¶
The flac encoding format comes in two flavors:
%flac
is the native flac format, useful for file output but not for streaming purpose%ogg(%flac,...)
is the ogg/flac format, which can be used to broadcast data with icecast
The parameters are:
%flac(samplerate=44100,
channels=2,
compression=5,
bits_per_sample=16)
compression
ranges from 0 to 8 and bits_per_sample
should be one of: 8
, 16
, 24
or 32
.
Please note that 32
bits per sample is currently not supported by the underlying libflac
.
FDK-AAC¶
This encoder can do both AAC and AAC+.
Its syntax is:
%fdkaac(channels=2, samplerate=44100, bandwidth="auto", bitrate=64, afterburner=false, aot="mpeg2_he_aac_v2", transmux="adts", sbr_mode=false)
Where aot
is one of: "mpeg4_aac_lc"
, "mpeg4_he_aac"
, "mpeg4_he_aac_v2"
,
"mpeg4_aac_ld"
, "mpeg4_aac_eld"
, "mpeg2_aac_lc"
, "mpeg2_he_aac"
or
"mpeg2_he_aac_v2"
bandwidth
is one of: "auto"
, any supported integer value.
transmux
is one of: "raw"
, "adif"
, "adts"
, "latm"
, "latm_out_of_band"
or "loas"
.
Bitrate can be either constant by passing: bitrate=64
or variable: vbr=<1-5>
You can consult the Hydrogenaudio knowledge base for more details on configuration values and meanings.
Gstreamer¶
The %gstreamer
encoder can be used to encode streams using the gstreamer
multimedia framework.
This encoder extends liquidsoap with all available GStreamer formats which includes most, if not all,
formats available to your operating system.
The encoder’s parameters are as follows:
%gstreamer(channels=2,
audio="lamemp3enc",
has_video=true,
video="x264enc",
muxer="mpegtsmux",
metadata="metadata",
log=5,
pipeline="")
Please refer to the Gstreamer encoder page for a detailed explanation of this encoder.
External encoders¶
For a detailed presentation of external encoders, see this page.
%external(channels=2,samplerate=44100,header=true,
restart_on_crash=false,
restart_on_metadata,
restart_after_delay=30,
process="progname")
Only one of restart_on_metadata
and restart_after_delay
should
be passed. The delay is specified in seconds.
The encoding process is mandatory, and can also be passed directly
as a string, without process=
.