Annotation of src/usr.bin/sndiod/sndiod.8, Revision 1.8
1.8 ! ratchov 1: .\" $OpenBSD: sndiod.8,v 1.7 2020/04/25 05:35:52 ratchov Exp $
1.1 ratchov 2: .\"
3: .\" Copyright (c) 2006-2012 Alexandre Ratchov <alex@caoua.org>
4: .\"
5: .\" Permission to use, copy, modify, and distribute this software for any
6: .\" purpose with or without fee is hereby granted, provided that the above
7: .\" copyright notice and this permission notice appear in all copies.
8: .\"
9: .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10: .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11: .\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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13: .\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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1.8 ! ratchov 17: .Dd $Mdocdate: April 25 2020 $
1.1 ratchov 18: .Dt SNDIOD 8
19: .Os
20: .Sh NAME
21: .Nm sndiod
22: .Nd audio/MIDI server
23: .Sh SYNOPSIS
24: .Nm sndiod
25: .Bk -words
26: .Op Fl d
27: .Op Fl a Ar flag
28: .Op Fl b Ar nframes
29: .Op Fl C Ar min : Ns Ar max
30: .Op Fl c Ar min : Ns Ar max
31: .Op Fl e Ar enc
1.3 ratchov 32: .Op Fl F Ar device
1.1 ratchov 33: .Op Fl f Ar device
34: .Op Fl j Ar flag
35: .Op Fl L Ar addr
36: .Op Fl m Ar mode
1.3 ratchov 37: .Op Fl Q Ar port
1.1 ratchov 38: .Op Fl q Ar port
39: .Op Fl r Ar rate
40: .Op Fl s Ar name
41: .Op Fl t Ar mode
42: .Op Fl U Ar unit
43: .Op Fl v Ar volume
44: .Op Fl w Ar flag
45: .Op Fl z Ar nframes
46: .Ek
47: .Sh DESCRIPTION
48: The
49: .Nm
50: daemon is an intermediate layer between
51: audio or MIDI programs and the hardware.
52: It performs the necessary audio processing to
53: allow any program to work on any supported hardware.
54: By default,
55: .Nm
56: accepts connections from programs
57: running on the same system only;
58: it initializes only when programs are using its services,
59: allowing
60: .Nm
61: to consume a negligible amount of system resources the rest of the time.
62: Systems with no audio hardware can use
63: .Nm
64: to keep hot-pluggable devices usable by default at
65: virtually no cost.
66: .Pp
67: .Nm
68: operates as follows: it exposes at least one
69: .Em sub-device
70: that any number of audio programs can connect to and use as if it was
71: audio hardware.
72: During playback,
73: .Nm
74: receives audio data concurrently from all programs, mixes it and sends
75: the result to the hardware device.
76: Similarly, during recording it duplicates audio data recorded
77: from the device and sends it to all programs.
78: Since audio data flows through the
79: .Nm
80: process, it has the opportunity to process audio data on the fly:
81: .Pp
82: .Bl -bullet -offset indent -compact
83: .It
84: Change the sound encoding to overcome incompatibilities between
85: software and hardware.
86: .It
87: Route the sound from one channel to another,
88: join stereo or split mono.
89: .It
90: Control the per-application playback volume as well as the
91: master volume.
92: .It
93: Monitor the sound being played, allowing one program to record
94: what other programs play.
95: .El
96: .Pp
97: Processing is configured on a per sub-device basis, meaning that
98: the sound of all programs connected to the same sub-device will be
99: processed according to the same configuration.
100: Multiple sub-devices can be defined, allowing multiple configurations
101: to coexist.
102: The user selects the configuration a given program will use
103: by selecting the sub-device the program uses.
104: .Pp
105: .Nm
106: exposes MIDI thru boxes (hubs),
107: allowing programs to send MIDI messages to each other
108: or to hardware MIDI ports in a uniform way.
109: .Pp
110: Finally,
111: .Nm
112: exposes a control MIDI port usable for:
113: .Pp
114: .Bl -bullet -offset indent -compact
115: .It
116: Volume control.
117: .It
118: Common clock source for audio and MIDI programs.
119: .It
120: Start, stop and relocate groups of audio programs.
121: .El
122: .Pp
123: The options are as follows:
124: .Bl -tag -width Ds
125: .It Fl a Ar flag
126: Control whether
127: .Nm
128: opens the audio device or the MIDI port only when needed or keeps
129: it open all the time.
130: If the flag is
131: .Va on
132: then the audio device or MIDI port is kept open all the time, ensuring
133: no other program can steal it.
134: If the flag is
135: .Va off ,
136: then it's automatically closed, allowing other programs to have direct
137: access to the audio device, or the device to be disconnected.
138: The default is
139: .Va off .
140: .It Fl b Ar nframes
141: The buffer size of the audio device in frames.
142: A frame consists of one sample for each channel in the stream.
143: This is the number of frames that will be buffered before being played
144: and thus controls the playback latency.
145: The default is 7680 or twice the block size
146: .Pq Fl z ,
147: if the block size is set.
148: .It Xo
149: .Fl C Ar min : Ns Ar max ,
150: .Fl c Ar min : Ns Ar max
151: .Xc
152: The range of channel numbers for recording and playback directions,
153: respectively any client is allowed to use.
154: This is a subset of the audio device channels.
155: The default is 0:1, i.e. stereo.
156: .It Fl d
1.2 ratchov 157: Enable debugging to standard error, and do not disassociate from the
158: controlling terminal.
159: Can be specified multiple times to further increase log verbosity.
1.1 ratchov 160: .It Fl e Ar enc
161: Attempt to configure the device to use this encoding.
162: The default is
163: .Va s16 .
164: Encoding names use the following scheme: signedness
165: .Po
166: .Va s
167: or
168: .Va u
169: .Pc
170: followed
171: by the precision in bits, the byte-order
172: .Po
173: .Va le
174: or
175: .Va be
176: .Pc ,
177: the number of
178: bytes per sample, and the alignment
179: .Po
180: .Va msb
181: or
182: .Va lsb
183: .Pc .
184: Only the signedness and the precision are mandatory.
185: Examples:
186: .Va u8 , s16le , s24le3 , s24le4lsb .
1.3 ratchov 187: .It Fl F Ar device
188: Specify an alternate device to use.
1.4 ratchov 189: If it doesn't work, the one given with the last
1.3 ratchov 190: .Fl f
191: or
192: .Fl F
193: options will be used.
194: For instance, specifying a USB device following a
195: PCI device allows
196: .Nm
197: to use the USB one preferably when it's connected
198: and to fall back to the PCI one when it's disconnected.
1.8 ! ratchov 199: Alternate devices may be switched with the
! 200: .Va server.device
! 201: control of the
! 202: .Xr sndioctl 1
! 203: utility.
1.1 ratchov 204: .It Fl f Ar device
205: Add this
206: .Xr sndio 7
207: audio device to devices used for playing and/or recording.
208: Preceding per-device options
209: .Pq Fl aberwz
210: apply to this device.
211: Sub-devices
212: .Pq Fl s
213: that are applied after will be attached to this device.
214: Device mode and parameters are determined from sub-devices
215: attached to it.
1.7 ratchov 216: If no
217: .Fl f
218: option is used,
219: .Nm
220: will use
221: .Pa rsnd/0 , rsnd/1 ,
222: .No ... ,
223: .Pa rsnd/3 .
1.1 ratchov 224: .It Fl j Ar flag
225: Control whether program channels are joined or expanded if
226: the number of channels requested by a program is not equal
227: to the device number of channels.
228: If the flag is
229: .Va off
230: then client channels are routed to the corresponding
231: device channel, possibly discarding channels not present in the device.
232: If the flag is
233: .Va on ,
234: then a single client channel may be sent on multiple device channels,
235: or multiple client channels may be sent to a single device channel.
236: For instance, this feature could be used for mono to stereo conversions.
237: The default is
238: .Ar on .
239: .It Fl L Ar addr
240: Specify a local network address
241: .Nm
242: should listen on;
243: .Nm
244: will listen on TCP port 11025+n, where n is the unit number
245: specified with
246: .Fl U .
247: Without this option,
248: .Nm
249: listens on the
250: .Ux Ns -domain
251: socket only, and is not reachable from any network.
252: If the option argument is
253: .Sq -
254: then
255: .Nm
256: will accept connections from any address.
257: As the communication is not secure, this
258: option is only suitable for local networks where all hosts
259: and users are trusted.
260: .It Fl m Ar mode
261: Set the sub-device mode.
262: Valid modes are
263: .Ar play ,
264: .Ar rec ,
265: and
266: .Ar mon ,
267: corresponding to playback, recording and monitoring.
268: A monitoring stream is a fake recording stream corresponding to
269: the mix of all playback streams.
270: Multiple modes can be specified, separated by commas,
271: but the same sub-device cannot be used for both recording and monitoring.
272: The default is
273: .Ar play , Ns Ar rec
274: (i.e. full-duplex).
1.3 ratchov 275: .It Fl Q Ar port
276: Specify an alternate MIDI port to use.
1.4 ratchov 277: If it doesn't work, the one given with the last
1.3 ratchov 278: .Fl Q
279: or
280: .Fl q
281: options will be used.
1.5 jmc 282: For instance, this allows a USB MIDI controller to be replaced without
1.3 ratchov 283: the need to restart programs using it.
1.1 ratchov 284: .It Fl q Ar port
285: Expose the given MIDI port.
286: This allows multiple programs to share the port.
1.6 ratchov 287: If no
288: .Fl q
289: option is used,
290: .Nm
291: will use
292: .Pa rmidi/0 , rmidi/1 ,
293: .No ... ,
294: .Pa rmidi/7 .
1.1 ratchov 295: .It Fl r Ar rate
296: Attempt to force the device to use this sample rate in Hertz.
297: The default is 48000.
298: .It Fl s Ar name
299: Add
300: .Ar name
301: to the list of sub-devices to expose.
302: This allows clients to use
303: .Nm
304: instead of the physical audio device for audio input and output
305: in order to share the physical device with other clients.
306: Defining multiple sub-devices allows splitting a physical audio device
307: into sub-devices having different properties (e.g. channel ranges).
308: The given
309: .Ar name
310: corresponds to the
311: .Dq option
312: part of the
313: .Xr sndio 7
314: device name string.
315: .It Fl t Ar mode
316: Select the way clients are controlled by MIDI Machine Control (MMC)
317: messages received by
318: .Nm .
319: If the mode is
320: .Va off
321: (the default), then programs are not affected by MMC messages.
322: If the mode is
323: .Va slave ,
324: then programs are started synchronously by MMC start messages;
325: additionally, the server clock is exposed as MIDI Time Code (MTC)
326: messages allowing MTC-capable software or hardware to be synchronized
327: to audio programs.
328: .It Fl U Ar unit
329: Unit number.
330: Each
331: .Nm
332: server instance has an unique unit number,
333: used in
334: .Xr sndio 7
335: device names.
336: The default is 0.
337: .It Fl v Ar volume
338: Software volume attenuation of playback.
339: The value must be between 1 and 127,
340: corresponding to \-42dB and \-0dB attenuation in 1/3dB steps.
341: Clients inherit this parameter.
342: Reducing the volume in advance allows a client's volume to stay independent
343: from the number of clients as long as their number is small enough.
344: 18 volume units (i.e. \-6dB attenuation) allows the number
345: of playback programs to be doubled.
346: The default is 118 i.e. \-3dB.
347: .It Fl w Ar flag
348: Control
349: .Nm
350: behaviour when the maximum volume of the hardware is reached
351: and a new program starts playing.
352: This happens only when volumes are not properly set using the
353: .Fl v
354: option.
355: If the flag is
356: .Va on ,
357: then the master volume is automatically adjusted to avoid clipping.
358: Using
359: .Va off
360: makes sense in the rare situation where all programs lower their volumes.
361: The default is
362: .Va on .
363: .It Fl z Ar nframes
364: The audio device block size in frames.
365: This is the number of frames between audio clock ticks,
366: i.e. the clock resolution.
367: If a sub-device is created with the
368: .Fl t
369: option, and MTC is used for synchronization, the clock
370: resolution must be 96, 100 or 120 ticks per second for maximum
371: accuracy.
372: For instance, 100 ticks per second at 48000Hz corresponds
373: to a 480 frame block size.
374: The default is 960 or half of the buffer size
375: .Pq Fl b ,
376: if the buffer size is set.
377: .El
378: .Pp
379: On the command line,
380: per-device parameters
381: .Pq Fl aberwz
382: must precede the device definition
383: .Pq Fl f ,
384: and per-sub-device parameters
385: .Pq Fl Ccjmtvx
386: must precede the sub-device definition
387: .Pq Fl s .
388: Sub-device definitions
389: .Pq Fl s
390: must follow the definition of the device
391: .Pq Fl f
392: to which they are attached.
393: .Pp
394: If no audio devices
395: .Pq Fl f
396: are specified,
397: settings are applied as if
398: the default device is specified.
399: If no sub-devices
400: .Pq Fl s
401: are specified for a device, a default sub-device is
402: created attached to it.
403: If a device
404: .Pq Fl f
405: is defined twice, both definitions are merged:
406: parameters of the first one are used but sub-devices
407: .Pq Fl s
408: of both definitions are created.
409: The default
410: .Xr sndio 7
411: device used by
412: .Nm
413: is
414: .Pa rsnd/0 ,
415: and the default sub-device exposed by
416: .Nm
417: is
418: .Pa snd/0 .
419: .Pp
420: If
421: .Nm
422: is sent
423: .Dv SIGINT
424: or
425: .Dv SIGTERM ,
426: it terminates.
1.3 ratchov 427: If
428: .Nm
429: is sent
430: .Dv SIGHUP ,
431: it reopens all audio devices and MIDI ports.
1.1 ratchov 432: .Pp
433: By default, when the program cannot accept
434: recorded data fast enough or cannot provide data to play fast enough,
435: the program is paused, i.e. samples that cannot be written are discarded
436: and samples that cannot be read are replaced by silence.
437: If a sub-device is created with the
438: .Fl t
439: option, then recorded samples are discarded,
440: but the same amount of silence will be written
441: once the program is unblocked, in order to reach the right position in time.
442: Similarly silence is played, but the same amount of samples will be discarded
443: once the program is unblocked.
444: This ensures proper synchronization between programs.
445: .Sh MIDI CONTROL
446: .Nm
447: creates a MIDI port with the same name as the exposed audio
448: sub-device to which MIDI programs can connect.
449: .Nm
450: exposes the audio device clock
451: and allows audio device properties to be controlled
452: through MIDI.
453: .Pp
454: A MIDI channel is assigned to each stream, and the volume
455: is changed using the standard volume controller (number 7).
456: Similarly, when the audio client changes its volume,
457: the same MIDI controller message is sent out; it can be used
458: for instance for monitoring or as feedback for motorized
459: faders.
460: .Pp
461: The master volume can be changed using the standard master volume
462: system exclusive message.
463: .Pp
464: Streams created with the
465: .Fl t
466: option are controlled by the following MMC messages:
467: .Bl -tag -width relocateXXX -offset indent
468: .It relocate
469: This message is ignored by audio
470: .Nm
471: clients, but the given time position is sent to MIDI ports as an MTC
472: .Dq "full frame"
473: message forcing all MTC-slaves to relocate to the given
474: position (see below).
475: .It start
476: Put all streams in starting mode.
477: In this mode,
478: .Nm
479: waits for all streams to become ready
480: to start, and then starts them synchronously.
481: Once started, new streams can be created
482: .Pq Nm sndiod
483: but they will be blocked
484: until the next stop-to-start transition.
485: .It stop
486: Put all streams in stopped mode (the default).
487: In this mode, any stream attempting to start playback or recording
488: is paused.
489: Client streams that are already
490: started are not affected until they stop and try to start again.
491: .El
492: .Pp
493: Streams created with the
494: .Fl t
495: option export the
496: .Nm
497: device clock using MTC, allowing non-audio
498: software or hardware to be synchronized to the audio stream.
499: Maximum accuracy is achieved when the number of blocks per
500: second is equal to one of the standard MTC clock rates (96, 100 and 120Hz).
501: The following sample rates
502: .Pq Fl r
503: and block sizes
504: .Pq Fl z
505: are recommended:
506: .Pp
507: .Bl -bullet -offset indent -compact
508: .It
509: 44100Hz, 441 frames (MTC rate is 100Hz)
510: .It
511: 48000Hz, 400 frames (MTC rate is 120Hz)
512: .It
513: 48000Hz, 480 frames (MTC rate is 100Hz)
514: .It
515: 48000Hz, 500 frames (MTC rate is 96Hz)
516: .El
517: .Pp
518: For instance, the following command will create two devices:
519: the default
520: .Va snd/0
521: and a MIDI-controlled
522: .Va snd/0.mmc :
523: .Bd -literal -offset indent
524: $ sndiod -r 48000 -z 400 -s default -t slave -s mmc
525: .Ed
526: .Pp
527: Streams connected to
528: .Va snd/0
529: behave normally, while streams connected to
530: .Va snd/0.mmc
531: wait for the MMC start signal and start synchronously.
532: Regardless of which device a stream is connected to,
533: its playback volume knob is exposed.
534: .Sh EXAMPLES
535: Start server using default parameters, creating an
536: additional sub-device for output to channels 2:3 only (rear speakers
537: on most cards), exposing the
538: .Pa snd/0
539: and
540: .Pa snd/0.rear
541: devices:
542: .Bd -literal -offset indent
543: $ sndiod -s default -c 2:3 -s rear
544: .Ed
545: .Pp
546: Start server creating the default sub-device with low volume and
547: an additional sub-device for high volume output, exposing the
548: .Pa snd/0
549: and
550: .Pa snd/0.max
551: devices:
552: .Bd -literal -offset indent
553: $ sndiod -v 65 -s default -v 127 -s max
554: .Ed
555: .Pp
556: Start server configuring the audio device to use
557: a 48kHz sample frequency, 240-frame block size,
558: and 2-block buffers.
559: The corresponding latency is 10ms, which is
560: the time it takes the sound to propagate 3.5 meters.
561: .Bd -literal -offset indent
562: $ sndiod -r 48000 -b 480 -z 240
563: .Ed
564: .Sh SEE ALSO
565: .Xr sndio 7
566: .Sh BUGS
567: Resampling is low quality; down-sampling especially should be avoided
568: when recording.
569: .Pp
570: Processing is done using 16-bit arithmetic,
571: thus samples with more than 16 bits are rounded.
572: 16 bits (i.e. 97dB dynamic) are largely enough for most applications though.
573: Processing precision can be increased to 24-bit at compilation time though.
574: .Pp
575: If
576: .Fl a Ar off
577: is used,
578: .Nm
579: creates sub-devices to expose first
580: and then opens the audio hardware on demand.
581: Technically, this allows
582: .Nm
583: to attempt to use one of the sub-devices it exposes as an audio device,
584: creating a deadlock.
585: There's nothing to prevent the user
586: from shooting himself in the foot by creating such a deadlock.
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