| Reading and writing MIDI files |
|---|
MIDIFILE:OPEN creates and returns a new
MIDIFILE:STREAM.
midifile:open file &key (direction :input) (if-exists :error)
format (ppqn 480) buffer-size
Note: FORMAT is 0 by default but if DIRECTION
is :OUTPUT and we write more than one MIDI track, the
FORMAT is automatically changed to 1 during MIDIFILE:CLOSE.
SCRATCH> (defvar *midi-file-test* "/tmp/test.mid") SCRATCH> (defparameter *mf* (midifile:open *midi-file-test* :direction :output :if-exists :supersede)) SCRATCH> (midifile:open-p *mf*) T SCRATCH> (midifile:input-stream-p *mf*) NIL SCRATCH> (midifile:output-stream-p *mf*) T SCRATCH> (midifile:path *mf*) #P"/tmp/test.mid" SCRATCH> (midifile:current-track *mf*) 0
MIDIFILE:NEXT-TRACK returns the number (zero based) of
the next track or NIL if the MIDIFILE:STREAM
is of type MIDIFILE:INPUT-STREAM and there aren't other
tracks to read.
MIDIFILE:NEXT-TRACK writes the current track if the
MIDIFILE:STREAM is of type MIDIFILE:OUTPUT-STREAM
;; Write the MIDI track 0 and start the track 1 SCRATCH> (midifile:next-track *mf*) 1 ;; Write the MIDI track 1 and start the track 2 SCRATCH> (midifile:next-track *mf*) 2 SCRATCH> (midifile:current-track *mf*) 2 ;; Write the MIDI tracks from 2 to 14 SCRATCH> (dotimes (i 13) (midifile:next-track *mf*)) SCRATCH> (midifile:current-track *mf*) 15 ;; Write the MIDI track 15 (the current track) and close the ;; MIDIFILE:OUTPUT-STREAM SCRATCH> (midifile:close *mf*) SCRATCH> (midifile:open-p *mf*) NIL
Reading MIDI file:
SCRATCH> (setf *mf* (midifile:open *midi-file-test*)) #<MIDIFILE:INPUT-STREAM :NUMBER-OF-TRACKS 16 :PPQN 480> SCRATCH> (midifile:input-stream-p *mf*) T SCRATCH> (midifile:output-stream-p *mf*) NIL
MIDIFILE:READ-HEADER reads the header of a MIDI file and
returns four values: format, number of tracks,
ppqn-or-smpte-format and ticks-per-frame.
SCRATCH> (midifile:read-header *mf*)
1
16
480
0
The methods to read the header fields are:
SCRATCH> (midifile:format *mf*) 1 SCRATCH> (midifile:number-of-tracks *mf*) 16 SCRATCH> (midifile:ppqn *mf*) 480 SCRATCH> (midifile:smpte *mf*) 0 0
These methods also work with a file name (or PATHNAME):
SCRATCH> (loop for f in '(midifile:format midifile:number-of-tracks midifile:ppqn midifile:smpte) collect (funcall f *midi-file-test*)) (1 16 480 0)
If the MIDI file contains a single tempo event, MIDIFILE:TEMPO
returns the tempo in BPM.
If there are more tempo changes, MIDIFILE:TEMPO returns
two lists: the values in BPM and the delta-times of the changes in beats
(useful to create a INCUDINE:TEMPO-ENVELOPE structure).
SCRATCH> (midifile:tempo *mf*) 120.0 SCRATCH> (midifile:close *mf*)
The next example writes a MIDI file with 16 empty tracks:
SCRATCH> (with-open-midifile (mf *midi-file-test* :direction :output :if-exists :supersede) (dotimes (i 15) (midifile:next-track mf)) *midi-file-test*)
MIDIFILE:READ-EVENT reads the next event from a
MIDIFILE:INPUT-STREAM and returns the status byte
or NIL if EOF.
A simple function to read the number of the events of a MIDI file is:
(defun number-of-midi-events (path) (with-open-midifile (mf path) (loop while (midifile:read-event mf) sum 1)))
The next example is a minimal MIDI player for Jack MIDI.
;; All the events are scheduled if the value of the configuration variable ;; *RT-EDF-HEAP-SIZE* in ${HOME}/.incudinerc is at least SCRATCH> (next-power-of-two (number-of-midi-events "/path/to/file.mid")) (defun play-midifile (port path) (with-schedule (with-open-midifile (mf path) (loop for st = (midifile:read-event mf) while st when (< st #xf0) do (at (* (midifile:event-seconds mf) *sample-rate*) #'jackmidi:write-short port (jackmidi:message st (midifile:message-data1 mf) (midifile:message-data2 mf)) (midifile:message-length mf)))))) SCRATCH> (rt-start) SCRATCH> (defparameter *midiout* (jackmidi:open :direction :output)) SCRATCH> (play-midifile *midiout* "/path/to/file.mid") SCRATCH> (rt-stop)
MIDIFILE:EVENT-SECONDS and MIDIFILE:EVENT-BEATS
return the time of the last event in seconds and beats, respectively.
MIDIFILE:EVENT-DELTA-TIME and MIDIFILE:EVENT-TIME
return delta-time and time of the current track, respectively.
MIDIFILE:MESSAGE-LENGTH returns the length of the last message
in bytes.
MIDIFILE:MESSAGE-BUFFER returns the internal buffer used to
store the MIDI messages and the length of the last message in bytes.
For example, the octets of the last message are
SCRATCH> (subseq (midifile:message-buffer mf) 0 (midifile:message-length mf))
We can use MIDIFILE:MESSAGE-STATUS, MIDIFILE:MESSAGE-DATA1
and MIDIFILE:MESSAGE-DATA2 to get status byte and data bytes of the
last MIDI message.
The method MIDIFILE:WRITE-HEADER writes the header-chunk of
a MIDI file. It works with CL:STREAM or MIDIFILE:OUTPUT-STREAM
SCRATCH> (with-open-file (f *midi-file-test* :direction :output :if-exists :supersede :element-type '(unsigned-byte 8)) (midifile:write-header f :format 1 :number-of-tracks 5 :ppqn-or-smpte-format 960)) SCRATCH> (midifile:read-header *midi-file-test*) 1 5 960 NIL 14 ; used internally
There are four utilities to write MIDI messages:
midifile:message status data1 data2
midifile:tempo-message bpm
midifile:string-message meta-event-type string
midifile:data &rest values
MIDIFILE:MESSAGE encodes a short MIDI message into a
(UNSIGNED-BYTE 32) for MIDIFILE:WRITE-SHORT-EVENT.
MIDIFILE:TEMPO-MESSAGE, MIDIFILE:STRING-MESSAGE
and MIDIFILE:DATA return the octets for MIDIFILE:WRITE-EVENT.
SCRATCH> (midifile:message #x90 60 100) 6569104 ; (on little-endian machines) SCRATCH> (midifile:tempo-message 135) #(255 81 3 6 200 28) SCRATCH> (midifile:string-message 3 "trackname") #(255 3 9 116 114 97 99 107 110 97 109 101) SCRATCH> (midifile:data #x90 60 100) #(144 60 100)
The syntax of MIDIFILE:WRITE-SHORT-EVENT and
MIDIFILE:WRITE-EVENT is
write-short-event mf beats msg size
write-event mf beats data &key (start 0) end
Note: we have to add MIDI events in chronological order; if the new event precedes the last event, it is added with delta-time zero.
MIDIFILE:WRITE-TEMPO-TRACK writes a track of a
MIDIFILE:OUTPUT-STREAM with the tempo changes obtained from
a INCUDINE:TEMPO-ENVELOPE. It fails if the current track
contains events at non-zero time.
SCRATCH> (defvar *tenv* (make-tempo-envelope '(96 135 120) '(8 12) :curve :step)) SCRATCH> (setf *mf* (midifile:open *midi-file-test* :direction :output :if-exists :supersede)) #<MIDIFILE:OUTPUT-STREAM :NUMBER-OF-TRACKS 1 :PPQN 480> SCRATCH> (midifile:write-event *mf* 0 (midifile:string-message 3 "tempo track")) 15 SCRATCH> (midifile:write-tempo-track *mf* *tenv*) 1 ; the next MIDI track SCRATCH> (midifile:write-event *mf* 0 (midifile:string-message 3 "one note")) 12 SCRATCH> (midifile:write-short-event *mf* 0 (midifile:message #x90 60 100) 3) 16 SCRATCH> (midifile:write-short-event *mf* 12 (midifile:message #x80 60 0) 3) 21 SCRATCH> (midifile:close *mf*) #<MIDIFILE:OUTPUT-STREAM :NUMBER-OF-TRACKS 2 :PPQN 480> SCRATCH> (midifile:tempo *midi-file-test*) (96.0 135.0 120.0) (8.0 12.0) SCRATCH> (with-open-midifile (mf *midi-file-test*) (loop for ev = (midifile:read-event mf) while ev collect (list (midifile:event-time mf) (midifile:event-delta-time mf) (midifile:event-beats mf) (midifile:event-seconds mf) (multiple-value-bind (buf len) (midifile:message-buffer mf) (subseq buf 0 len))))) (( 0 0 0.0d0 0.0d0 #(255 3 11 116 101 109 112 111 32 116 114 97 99 107)) ( 0 0 0.0d0 0.0d0 #(255 81 3 9 137 104)) (3840 3840 8.0d0 5.0d0 #(255 81 3 6 200 28)) (9600 5760 20.0d0 10.333328d0 #(255 81 3 7 161 32)) ( 0 0 0.0d0 0.0d0 #(255 47 0)) ; EOT (time ignored) ( 0 0 0.0d0 0.0d0 #(255 3 8 111 110 101 32 110 111 116 101)) ( 0 0 0.0d0 0.0d0 #(144 60 100)) (5760 5760 12.0d0 6.777776d0 #(128 60 0)) (5760 0 12.0d0 6.777776d0 #(255 47 0))) ; EOT
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