The package contains decoder, player and encoder bindings. Playback uses the existing audio player modules. Encoding is provided by audio-encoder.rkt with Opus and FLAC backends.

Native dependencies

For playback and decoding, install the native libraries used by the selected backends:

libao
libFLAC
mpg123
FFmpeg libraries, including libavutil, libavcodec and libavformat

For encoding, also install:

libopusenc
libopus
libogg
TagLib with the C binding, usually provided as taglib / taglib_c
libsoxr, used by resampler.rkt and encoder-side PCM sample-rate conversion

The Opus encoder backend uses libopusenc directly. The FLAC encoder backend uses libFLAC directly. FLAC sample-rate conversion uses resampler.rkt, backed by libsoxr. Metadata and cover-art copying use the TagLib wrapper; the public taglib.rkt API also supports read-write tag editing.

Debian / Ubuntu

On Debian-like systems, install the runtime and development packages for the selected backends. A typical full setup is:

sudo apt install \
  libao-dev \
  libflac-dev \
  libmpg123-dev \
  ffmpeg \
  libavutil-dev libavcodec-dev libavformat-dev libswresample-dev \
  libogg-dev libopus-dev libopusenc-dev libopusfile-dev \
  libsoxr-dev libtag1-dev

For Opus encoding, libopusenc-dev is required. For Opus decoding through opusfile-decoder.rkt, install libopusfile-dev as well.

macOS

Using Homebrew, install the native libraries before using the package:

brew install libao
brew install flac
brew install mpg123
brew install ffmpeg
brew install opus
brew install libopusenc
brew install libsoxr
brew install taglib

Some Homebrew installations provide FFmpeg as ffmpeg; older local setups may use ffmpeg-full.

Windows

On Windows, the package downloader fetches the native DLL bundle from the Codeberg racket-sound-lib release area. The current bundle URL pattern is:

https://codeberg.org/hnmdijkema/racket-sound-lib/releases/download/1-1-2/windows-x86_64.zip

The archive is installed below Racket's addon directory by download-soundlibs.

Encoder examples

Encode to Opus:

(require "audio-encoder.rkt")

(audio-encode "input.flac"
              "output.opus"
              (hash 'bitrate 224000
                    'vbr? #t
                    'complexity 10)
              #:encoder 'opus)

Encode 96 kHz FLAC to 48 kHz FLAC:

(audio-encode "input-96k.flac"
              "output-48k.flac"
              (hash 'sample-rate 48000
                    'bits-per-sample 24
                    'compression-level 8)
              #:encoder 'flac)

A small test wrapper is available in encoder-test.rkt:

racket encoder-test.rkt --encoder opus --input input.flac --output output.opus --bitrate-kbps 224
racket encoder-test.rkt --encoder flac --input input-96k.flac --output output-48k.flac --sample-rate 48000

Placed player stdio mode

The placed player can also run as a standard-port worker. In that mode the three existing logical channels are mapped to standard streams:

stdin   command channel
stdout  reply channel
stderr  event channel

Because stdout and stderr are protocol streams in this mode, ordinary display and log output is redirected. By default, placed-player/stdio appends such output to a log file below Racket's standard cache directory, for example ~/.cache/racket/racket-audio/placed-audio-player-stdio.log on many Unix-like systems. Pass #:log-file #f to discard ordinary output, or pass a path to choose a different log file.

Remote placed player over SSH

The placed player can also be started as a remote subprocess over SSH. In this mode the existing three logical player channels are kept separate:

stdin   command channel
stdout  reply channel
stderr  event channel

The remote worker is normally started as:

racket -l racket-audio/audio-placed-player -- --stdio

The worker redirects ordinary logging to a cache log file so that stdout and stderr remain serialized protocol streams. SSH, the remote Racket command and the remote module are configured in racket-audio.ini. The public make-audio-player API only needs the remote host and, when necessary, base path replacements.

Example:

(define player
  (make-audio-player cb-state cb-eof
                     #:remote-host "nas"
                     #:replace-base-paths
                     (list (cons "/muziek" "/volume1/music"))))

(audio-play! player "/muziek/klassiek/track.flac")

The remote host must be able to read the translated path. In the example above, the remote worker receives /volume1/music/klassiek/track.flac.