gemigreerd-racket-audio/README.md

racket-audio

Integration of common audio libraries in Racket.

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, libavformat and libswresample

For encoding, also install:

• libopusenc
• libopus
• libogg
• TagLib with the C binding, usually provided as taglib / taglib_c

The Opus encoder backend uses libopusenc directly. The FLAC encoder backend uses libFLAC directly. FLAC sample-rate conversion uses the existing FFmpeg swresample layer. Metadata and cover-art copying use the TagLib wrapper; the public taglib.rkt API also supports read-write tag editing.

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 taglib

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

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