Skip to content

Instantly share code, notes, and snippets.

Last active Aug 16, 2020
What would you like to do?
mpg123 - port audio chez example
#!/usr/bin/env scheme-script
;; -*- mode: scheme; coding: utf-8 -*- !#
;; Copyright (c) 2020 Julian Herrera
;; SPDX-License-Identifier: MIT
(import (chezscheme)(prefix (mpg123) mpg123:)(lento))
(define lib-portaudio (load-shared-object ""))
(define-syntax define-function
(syntax-rules ()
((_ ret name fpname args)
(define name
(foreign-procedure (symbol->string 'fpname) args ret)))))
;; PortAudio typedefs
(define-ftype PaError int)
(define-ftype PaDeviceIndex int)
(define-ftype PaSampleFormat unsigned-long)
(define-ftype PaTime double)
(define-ftype PaHostApiIndex int)
(define-ftype PaStreamFlags unsigned-long)
(define-ftype PPaStream void*) ; void isn't valid as a chez FFI type,
; instead store pointer to void stream
(define done-ptr (make-ftype-pointer size_t (foreign-alloc (ftype-sizeof size_t))))
;; Constants
(define pa:int16 #x00000008)
(define pa:clip-off #x00000001)
;; PortAudio structs
(define-ftype PaStreamParameters
[device PaDeviceIndex]
[channelCount int]
[sampleFormat PaSampleFormat]
[suggestedLatency PaTime]
[hostApiSpecificStreamInfo void*]))
(define-ftype PaDeviceInfo
[structVersion int]
[name (* char)]
[hostApi PaHostApiIndex]
[maxInputChannels int]
[maxOutputChannels int]
[defaultLowInputLatency PaTime]
[defaultLowOutputLatency PaTime]
[defaultHighInputLatency PaTime]
[defaultHighOutputLatency PaTime]))
;; ;; PortAudio Functions
(define-function PaError %pa:initialize Pa_Initialize ())
(define-function PaError pa:terminate Pa_Terminate ())
(define-function string pa:get-error-text Pa_GetErrorText (PaError))
(define-function PaDeviceIndex pa:get-default-output-device Pa_GetDefaultOutputDevice ())
(define-function (* PaDeviceInfo) pa:get-device-info Pa_GetDeviceInfo (PaDeviceIndex))
(define-function PaError pa:open-stream Pa_OpenStream
((* PPaStream)
(* PaStreamParameters)
(define-function PaError pa:start-stream Pa_StartStream (void*))
(define-function PaError pa:write-stream Pa_WriteStream (void* void* unsigned-long))
(define-function PaError pa:stop-stream Pa_StopStream (void*))
(define-function PaError pa:close-stream Pa_CloseStream (void*))
(define (pa:initialize)
(let ([err (%pa:initialize)])
(if (not (zero? err))
(pa:handle-error err)
(display "portaudio initialized")
(define (pa:handle-error err)
(let ([error-text (pa:get-error-text err)])
(display error-text)
;; ;; Initialize the Application
(define rate)
(define channels)
(define encoding)
(define handle (mpg123:new-handle))
;; the filename is the first (and only) item in the list `command-line-arguments`
(define audio-file (car (command-line-arguments)))
;; open the audio file, passing in the handle to which you attach everything.
(mpg123:open-stream handle audio-file)
;; once more, handle goes, as well as ADDRESSES to
(mpg123:get-format handle (lambda (r c e)
(set! rate r)
(set! channels c)
(set! encoding e)))
;; ;; foreign-refs to these now show updated values
;; ;; allocate space for the stream parameter struct that needs initializing
(define output-parameters-ptr
(make-ftype-pointer PaStreamParameters
(foreign-alloc (ftype-sizeof PaStreamParameters))))
(define stream (make-ftype-pointer PPaStream (foreign-alloc (ftype-sizeof PPaStream))))
(define output-device (pa:get-default-output-device))
(define device-info-ptr (pa:get-device-info output-device))
;; set values on our PaStreamParameters pointer: output-parameters-ptr
(ftype-set! PaStreamParameters
output-parameters-ptr output-device)
(ftype-set! PaStreamParameters
(ftype-set! PaStreamParameters
output-parameters-ptr pa:int16)
(ftype-set! PaStreamParameters
(ftype-ref PaDeviceInfo
(defaultHighOutputLatency) device-info-ptr))
(ftype-set! PaStreamParameters
output-parameters-ptr 0)
(pa:open-stream stream ; call to open the stream, first passing the stream-ptr
0 ; inputStream params ptr, nul(0) byte for output stream
output-parameters-ptr ; outputStream params ptr
(* rate 1.0) ; extract rate value from rate ptr
0 ; 0 so the system determines the optimal frames per buffer
(define stream-ptr (foreign-ref 'void* (ftype-pointer-address stream) 0)) ;;whats at the pointer to the pointer
(define buffer-size (mpg123:outblock handle))
(define output-buffer (foreign-alloc buffer-size))
(pa:start-stream stream-ptr)
(let play ([sample 0]
[done #f])
(guard (x [(warning? x) (set! done #t)])
(mpg123:read-stream handle output-buffer buffer-size done-ptr))
(pa:write-stream stream-ptr output-buffer (/ buffer-size 4))
(if (not done)
(play (+ 1 sample) done)))
(pa:stop-stream stream-ptr)
(pa:close-stream stream-ptr)
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment