midialsa.lua


NAME

midialsa.lua - the ALSA library, plus some interface functions


SYNOPSIS

 local ALSA = require 'midialsa'
 ALSA.client( 'Lua client', 1, 1, false )
 ALSA.connectfrom( 0, 14, 0 )    --  input port is lower (0)
 ALSA.connectto( 1, 'TiMidity' ) -- output port is higher (1)
 while true do
     local alsaevent = ALSA.input()
     if alsaevent[1] == ALSA.SND_SEQ_EVENT_PORT_UNSUBSCRIBED then break end
     if alsaevent[1] == ALSA.SND_SEQ_EVENT_NOTEON then
         local channel  = alsaevent[8][1]
         local pitch    = alsaevent[8][2]
         local velocity = alsaevent[8][3]
     elseif alsaevent[1] == ALSA.SND_SEQ_EVENT_CONTROLLER then
         local channel    = alsaevent[8][1]
         local controller = alsaevent[8][5]
         local value      = alsaevent[8][6]
     end
     ALSA.output( alsaevent )
 end


DESCRIPTION

This module offers a Lua interface to the ALSA library. It translates into Lua the Python modules alsaseq.py and alsamidi.py by Patricio Paez; it also offers some functions to translate events from and to the format used in Peter Billam's MIDI.lua Lua module and Sean Burke's MIDI-Perl CPAN module.

This module is in turn translated also into a call-compatible Perl CPAN module: MIDI::ALSA

As from version 1.15, note durations are in seconds rather than milliseconds, for consistency with the timestamps. This introduces a backward incompatibility which only affects you if are putting together your own alsaevents without using the noteevent() function. In the worst case you have to detect versions:

 if tonumber(ALSA.Version) < 1.145 then
    alsaevent[8][5] = 1000*alsaevent[8][5]
 end


FUNCTIONS

Functions based on those in alsaseq.py: client(), connectfrom(), connectto(), disconnectfrom(), disconnectto(), fd(), id(), input(), inputpending(), output(), start(), status(), stop() and syncoutput()

Functions based on those in alsamidi.py: noteevent(), noteonevent(), noteoffevent(), pgmchangeevent(), pitchbendevent(), controllerevent(), chanpress() and sysex()

Functions to interface with MIDI.lua: alsa2scoreevent() and scoreevent2alsa()

Functions to to get the current ALSA status: listclients(), listnumports(), listconnectedto(), listconnectedfrom() and parse_address()

client( name, ninputports, noutputports, createqueue )

Create an ALSA sequencer client with zero or more input or output ports, and optionally a timing queue. ninputports and noutputports are created if the quantity requested is between 1 and 64 for each. If createqueue = true, it creates a queue for stamping the arrival time of incoming events and scheduling future start times of outgoing events.
For full ALSA functionality, the name should contain only letters, digits, underscores, equal-signs or spaces, and should contain at least one letter.
Unlike in the alsaseq.py Python module, it returns success or failure.

connectfrom( inputport, src_client, src_port )

Connect from src_client:src_port to my inputport. Each input port can connect from more than one client. The input() function will receive events from any intput port and any of the clients connected to each of them. Events from each client can be distinguished by their source field.
Unlike in the alsaseq.py Python module, it returns success or failure.
Unlike in the alsaseq.py Python module, if src_client is a string and src_port is undefined, then parse_address(src_client) automatically gets invoked. This allows you to refer to the src_client by name, for example connectfrom(inputport,'Virtual:1') will connect from port 1 of the 'Virtual Raw MIDI' client.

connectto( outputport, dest_client, dest_port )

Connect my outputport to dest_client:dest_port. Each outputport can connect to more than one client. Events sent to an output port using the output() funtion will be sent to all clients that are connected to it using this function.
Unlike in the alsaseq.py Python module, it returns success or failure.
Unlike in the alsaseq.py Python module, if dest_client is a string and dest_port is undefined, then parse_address(dest_client) automatically gets invoked. This allows you to refer to the dest_client by name, for example connectto(outputport,'Roland XV-2020') will connect to port 0 of the 'Roland XV-2020' client.

disconnectfrom( inputport, src_client, src_port )

Disconnect the connection from the remote src_client:src_port to my inputport.
Returns success or failure.
Unlike in the alsaseq.py Python module, if src_client is a string and src_port is undefined, then parse_address(src_client) automatically gets invoked. This allows you to refer to the src_client by name, for example disconnectfrom(inputport,'Virtual:1') will disconnect from port 1 of the 'Virtual Raw MIDI' client.

disconnectto( outputport, dest_client, dest_port )

Disconnect the connection from my outputport to the remote dest_client:dest_port.
Returns success or failure.
Unlike in the alsaseq.py Python module, if dest_client is a string and dest_port is undefined, then parse_address(dest_client) automatically gets invoked. This allows you to refer to the dest_client by name, for example disconnectto(outputport,'Virtual:2') will disconnect to port 2 of the 'Virtual Raw MIDI' client.

fd()

Return fileno of sequencer.

id()

Return the client number, or 0 if the client is not yet created.

input()

Wait for an ALSA event in any of the input ports and return it. ALSA events are returned as an array with 8 elements:

 {type, flags, tag, queue, time, source, destination, data}

Unlike in the alsaseq.py Python module, the time element is in floating-point seconds. The last three elements are also arrays:

 source = { src_client,  src_port }
 destination = { dest_client,  dest_port }
 data = { varies depending on type }

The source and destination arrays may be useful within an application for handling events differently according to their source or destination. The event-type constants, beginning with SND_SEQ_, are available as module variables.

Note that if the event is of type SND_SEQ_EVENT_PORT_SUBSCRIBED or SND_SEQ_EVENT_PORT_UNSUBSCRIBED, then that message has come from the System, and its dest_port tells you which of your ports is involved. But its src_client and src_port do not tell you which other client connected or disconnected; you'll need to use listconnectedfrom() or listconnectedto() to see what's happened.

The data array is mostly as documented in http://alsa-project.org/alsa-doc/alsa-lib/seq.html
For NOTE events, the elements are { channel, pitch, velocity, unused, duration }
where the duration is in floating-point seconds (unlike in the alsaseq.py Python module where it is in milliseconds).
For SYSEX, the data array has just one element: the byte-string, including any F0 and F7 bytes.
For most other events, the elements are { channel, unused,unused,unused, param, value }

The channel element is always 0..15
In the SND_SEQ_EVENT_PITCHBEND event the value element is from -8192..+8191; logical, but not the more usual 0..16383

inputpending()

Return the number of bytes available in input buffer. Use before input() to wait till an event is ready to be read. If a connection terminates, then inputpending() returns, and the next event will be of type SND_SEQ_EVENT_PORT_UNSUBSCRIBED

output( { type, flags, tag, queue, time, source, destination, data } )

Send an ALSA-event to an output port. The format of the event is as discussed in input() above. The event will be output immediately either if no queue was created in the client or if the queue parameter is set to ALSA.SND_SEQ_QUEUE_DIRECT, and otherwise it will be queued and scheduled.

The source is an array with two elements:   {src_client, src_port},   specifying the local output-port from which the event will be sent. If only one output-port exists, all events are sent from it. If two or more exist, the src_port determines which to use. The smallest available port-number (as created by client()) will be used if src_port is less than it, and the largest available will be used if src_port is greater than it.

The destination is an array with two elements:   {dest_client, dest_port},   specifying the remote client/port to which the event will be sent. If dest_client is zero, (as generated by scoreevent2alsa() or noteevent()), or is the same as the local client (as generated by input()), then the event will be sent to all clients that the local port is connected to (see connectto() and listconnectedto()). But if you set dest_client to a remote client, then the event will be sent to that dest_client:dest_port and nowhere else.

It is possible to send an event to a destination to which there is no connection, but it's not usually the right thing to do. Normally, you should set up a connection, to allow the underlying RawMIDI ports to remain open while playing; otherwise, ALSA will reset the port after every event.

If the queue buffer is full, output() will wait until space is available to output the event. Use status() to know how many events are scheduled in the queue.

If no queue has been started, a SND_SEQ_EVENT_NOTE event can only emerge as a SND_SEQ_EVENT_NOTEON, since a queue is necessary in order to schedule the corresponding NOTEOFF.

start()

Start the queue. It is ignored if the client does not have a queue.

status()

Return { status, time, events } of the queue.

 Status: 0 if stopped, 1 if running.
 Time: current time in seconds.
 Events: number of output events scheduled in the queue.

If the client does not have a queue the value {0,0,0} is returned. Unlike in the alsaseq.py Python module, the time element is in floating-point seconds.

stop()

Stop the queue. It is ignored if the client does not have a queue.

syncoutput()

Wait until output events are processed.

noteevent( ch, key, vel, start, duration )

Returns an ALSA-event-array, ready to be scheduled by output(). Unlike in the alsaseq.py Python module, the start and duration elements are in floating-point seconds.

noteonevent( ch, key, vel, start )

Returns an ALSA-event-array, ready to be scheduled by output(). If start is not used, the event will be sent directly. Unlike in the alsaseq.py Python module, if start is provided, the event will be scheduled in a queue. The start element, when provided, is in floating-point seconds.

noteoffevent( ch, key, vel, start )

Returns an ALSA-event-array, ready to be scheduled by output(). If start is not used, the event will be sent directly. Unlike in the alsaseq.py Python module, if start is provided, the event will be scheduled in a queue. The start element, when provided, is in floating-point seconds.

pgmchangeevent( ch, value, start )

Returns an ALSA-event-array for a patch_change to be sent by output(). If start is not used, the event will be sent directly; if start is provided, the event will be scheduled in a queue. Unlike in the alsaseq.py Python module, the start element, when provided, is in floating-point seconds.

pitchbendevent( ch, value, start )

Returns an ALSA-event-array to be sent by output(). The value is from -8192 to 8191. If start is not used, the event will be sent directly; if start is provided, the event will be scheduled in a queue. Unlike in the alsaseq.py Python module, the start element, when provided, is in floating-point seconds.

(Note that fluidsynth uses a different convention, in which the value is from 0 to 16383 and 8192 represents the central position.)

controllerevent( ch, controllernum, value, start )

Returns an ALSA-event-array to be sent by output(). If start is not used, the event will be sent directly; if start is provided, the event will be scheduled in a queue. Unlike in the alsaseq.py Python module, the start element, when provided, is in floating-point seconds.

chanpress( ch, value, start )

Returns an ALSA-event-array to be sent by output(). If start is not used, the event will be sent directly; if start is provided, the event will be scheduled in a queue. Unlike in the alsaseq.py Python module, the start element, when provided, is in floating-point seconds.

sysex( ch, string, start )

Returns an ALSA-event-array to be sent by output(). If start is not used, the event will be sent directly; if start is provided, the event will be scheduled in a queue. The string should start with your Manufacturer ID, but should not contain any of the F0 or F7 bytes, they will be added automatically; indeed the string must not contain any bytes with the top-bit set.

alsa2scoreevent( alsaevent )

Returns an event in the millisecond-tick score-format used by the MIDI.lua and MIDI.py modules, based on the score-format in Sean Burke's MIDI-Perl CPAN module. See: MIDI.html#events

Since it combines a note_on and a note_off event into one note event, it will return nil when called with the note_on event; the calling loop must therefore detect nil and not, for example, try to index it.

scoreevent2alsa( scoreevent )

Returns an ALSA-event-array to be scheduled in a queue by output(). The input is an event in the millisecond-tick score-format used by the MIDI.lua and MIDI.py modules, based on the score-format in Sean Burke's MIDI-Perl CPAN module.   See: MIDI.html#events.   For example:
ALSA.output(ALSA.scoreevent2alsa{'note',4000,1000,0,62,110})
Some events in a .mid file have no equivalent real-time-midi event, which is the sort that ALSA deals in; these events will cause scoreevent2alsa() to return nil. Therefore if you are going through the events in a midi score converting them with scoreevent2alsa(), you should check that the result is not nil before doing anything further.

listclients()

Returns a table with the client-numbers as key and the descriptive strings of the ALSA client as value :
local clientnumber2clientname = ALSA.listclients()

listnumports()

Returns a table with the client-numbers as key and how many ports they are running as value, so if a client is running 4 ports they will be numbered 0..3
local clientnumber2howmanyports = ALSA.listnumports()

listconnectedto()

Returns an array of three-element arrays { {outputport, dest_client, dest_port}, } with the same data as might have been passed to connectto(), or which could be passed to disconnectto().

listconnectedfrom()

Returns an array of three-element arrays { {inputport, src_client, src_port}, } with the same data as might have been passed to connectfrom(), or which could be passed to disconnectfrom().

parse_address( client_name )

Given a string, this function returns two integers, client_number and port_number, as might be needed by connectto() or connectfrom(). For example, even if client() has not been called, "24" will return 24,0 and "25:1" will return 25,1

If the local client is running, then parse_address() also looks up names. For example, if aconnect -oil reveals a timidity client:
    client 128: 'TiMidity' [type=user]
then parse_address("TiM") will return 128,0 and parse_address("TiMi:1") will return 128,1 because it finds the first client with a start-of-string case-sensitive match to the given name.
parse_address() is called automatically by connectto(), connectfrom(), disconnectto() and disconnectfrom() if they are called with the second argument a string and the third argument undefined.
parse_address() was introduced in version 1.11 and is not present in the alsaseq.py Python module.


CONSTANTS

SND_SEQ_EVENT_BOUNCE     SND_SEQ_EVENT_CHANPRESS     SND_SEQ_EVENT_CLIENT_CHANGE     SND_SEQ_EVENT_CLIENT_EXIT     SND_SEQ_EVENT_CLIENT_START     SND_SEQ_EVENT_CLOCK     SND_SEQ_EVENT_CONTINUE     SND_SEQ_EVENT_CONTROL14     SND_SEQ_EVENT_CONTROLLER     SND_SEQ_EVENT_ECHO     SND_SEQ_EVENT_KEYPRESS     SND_SEQ_EVENT_KEYSIGN     SND_SEQ_EVENT_NONE     SND_SEQ_EVENT_NONREGPARAM     SND_SEQ_EVENT_NOTE     SND_SEQ_EVENT_NOTEOFF     SND_SEQ_EVENT_NOTEON     SND_SEQ_EVENT_OSS     SND_SEQ_EVENT_PGMCHANGE     SND_SEQ_EVENT_PITCHBEND     SND_SEQ_EVENT_PORT_CHANGE     SND_SEQ_EVENT_PORT_EXIT     SND_SEQ_EVENT_PORT_START     SND_SEQ_EVENT_PORT_SUBSCRIBED     SND_SEQ_EVENT_PORT_UNSUBSCRIBED     SND_SEQ_EVENT_QFRAME     SND_SEQ_EVENT_QUEUE_SKEW     SND_SEQ_EVENT_REGPARAM     SND_SEQ_EVENT_RESET     SND_SEQ_EVENT_RESULT     SND_SEQ_EVENT_SENSING     SND_SEQ_EVENT_SETPOS_TICK     SND_SEQ_EVENT_SETPOS_TIME     SND_SEQ_EVENT_SONGPOS     SND_SEQ_EVENT_SONGSEL     SND_SEQ_EVENT_START     SND_SEQ_EVENT_STOP     SND_SEQ_EVENT_SYNC_POS     SND_SEQ_EVENT_SYSEX     SND_SEQ_EVENT_SYSTEM     SND_SEQ_EVENT_TEMPO     SND_SEQ_EVENT_TICK     SND_SEQ_EVENT_TIMESIGN     SND_SEQ_EVENT_TUNE_REQUEST     SND_SEQ_EVENT_USR0     SND_SEQ_EVENT_USR1     SND_SEQ_EVENT_USR2     SND_SEQ_EVENT_USR3     SND_SEQ_EVENT_USR4     SND_SEQ_EVENT_USR5     SND_SEQ_EVENT_USR6     SND_SEQ_EVENT_USR7     SND_SEQ_EVENT_USR8     SND_SEQ_EVENT_USR9     SND_SEQ_EVENT_USR_VAR0     SND_SEQ_EVENT_USR_VAR1     SND_SEQ_EVENT_USR_VAR2     SND_SEQ_EVENT_USR_VAR3     SND_SEQ_EVENT_USR_VAR4     SND_SEQ_QUEUE_DIRECT     SND_SEQ_TIME_STAMP_REAL     Version     VersionDate

The MIDI standard specifies that a NOTEON event with velocity=0 means the same as a NOTEOFF event; so you may find a little function like this convenient:

 local function is_noteoff(alsaevent)
    if alsaevent[1] == ALSA.SND_SEQ_EVENT_NOTEOFF then return true end
    if alsaevent[1] == ALSA.SND_SEQ_EVENT_NOTEON and alsaevent[8][3] == 0 then
       return true
    end
    return false
 end
Since Version 1.20, the output-ports are marked as WRITE, so they can receive SND_SEQ_EVENT_PORT_SUBSCRIBED or SND_SEQ_EVENT_PORT_UNSUBSCRIBED events from System Announce.
Up until Version 1.19, and in the original Python module, output-ports created by client() were not so marked; in those days, if knowing about connections and disconnections to the output-port was important, you had to listen to all notifications from System Announce: ALSA.connectfrom(0,'System:1') This alerted you unnecessarily to events which didn't involve your client, and the connection showed up confusingly in the output of aconnect -oil


DOWNLOAD

This module is available as a LuaRock in rocks.moonscript.org/modules/peterbillam so you should be able to install it with the command:
  $ su
  Password:
  # luarocks install --server=http://rocks.moonscript.org midialsa

or:
  # luarocks install http://www.pjb.com.au/comp/lua/midialsa-1.21-0.rockspec

If this results in an error message such as:
  Error: Could not find expected file libasound.a, or libasound.so,
  or libasound.so.* for ALSA -- you may have to install ALSA in your
  system and/or pass ALSA_DIR or ALSA_LIBDIR to the luarocks command.
  Example: luarocks install midialsa ALSA_DIR=/usr/local

then you need to find the appropriate directory with:
  find /usr/lib -name 'libasound.*' -print
and then invoke:
  luarocks install \
  http://www.pjb.com.au/comp/lua/midialsa-1.21-0.rockspec \
  ALSA_LIBDIR=/usr/lib/i386-linux-gnu/ # or wherever

accordingly.


CHANGES


20140609 1.21 switch pod and doc over to using moonrocks
20140416 1.20 outputports marked WRITE to get UNSUBSCRIBED messages from System
20140404 1.19 (dis)connect(to,from) use the new parse_address; some doc fixes
20130514 1.18 parse_address matches startofstring to hide an alsa-lib 1.0.24 bug
20130211 1.18 noteonevent and noteoffevent accept a start parameter
20121208 1.17 test script handles alsa_1.0.16 quirk
20121206 1.16 queue_id; test prints better diagnostics; 5.2-compatible
20120930 1.15 output() timestamp and duration in floating-point seconds
20111112 1.14 but output() does broadcast if destination is self
20111108 1.12 output() does not broadcast if destination is set
20111101 1.11 add parse_address() and call automatically from connectto() etc
20110624 1.09 maximum_nports increased from 4 to 64
20110428 1.06 fix bug in status() in the time return-value
20110323 1.05 controllerevent()
20110303 1.04 output, input, *2alsa and alsa2* now handle sysex events
20110228 1.03 add listclients, listconnectedto and listconnectedfrom
20110213 1.02 add disconnectto and disconnectfrom
20110210 1.01 output() no longer floors the time to the nearest second
20110209 1.01 pitchbendevent() and chanpress() return correct data
20110129 1.00 first working version


TO DO

Perhaps there should be a general connect_between() mechanism, allowing the interconnection of two other clients, a bit like aconnect 32 20

ALSA does not transmit Meta-Events like text_event, and there's not much can be done about that.


AUTHOR

Peter J Billam, http://www.pjb.com.au/comp/contact.html


SEE ALSO

 aconnect -oil
 http://pp.com.mx/python/alsaseq
 http://search.cpan.org/perldoc?MIDI::ALSA
 http://www.pjb.com.au/comp/lua/midialsa.html
 http://rocks.moonscript.org/modules/peterbillam/midialsa
 http://www.pjb.com.au/comp/lua/fluidsynth.html
 http://www.pjb.com.au/comp/lua/MIDI.html
 http://www.pjb.com.au/comp/lua/MIDI.html#events
 http://alsa-project.org/alsa-doc/alsa-lib/seq.html
 http://alsa-project.org/alsa-doc/alsa-lib/group___seq_events.html
 http://alsa-project.org/alsa-doc/alsa-lib/structsnd__seq__ev__note.html
 http://alsa-project.org/alsa-doc/alsa-lib/structsnd__seq__ev__ctrl.html
 http://alsa-project.org/alsa-doc/alsa-lib/structsnd__seq__ev__queue__control.html
 http://alsa-project.org/alsa-doc/alsa-lib/group___seq_client.html
 http://alsa-utils.sourcearchive.com/documentation/1.0.20/aconnect_8c-source.html
 http://alsa-utils.sourcearchive.com/documentation/1.0.8/aplaymidi_8c-source.html
 snd_seq_client_info_event_filter_clear
 snd_seq_get_any_client_info
 snd_seq_get_client_info
 snd_seq_client_info_t