Annotation of src/usr.bin/sndiod/sndiod.8, Revision 1.5
1.5 ! jmc 1: .\" $OpenBSD: sndiod.8,v 1.4 2019/09/21 05:03:34 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
12: .\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13: .\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14: .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15: .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16: .\"
1.4 ratchov 17: .Dd $Mdocdate: September 21 2019 $
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.
1.1 ratchov 199: .It Fl f Ar device
200: Add this
201: .Xr sndio 7
202: audio device to devices used for playing and/or recording.
203: Preceding per-device options
204: .Pq Fl aberwz
205: apply to this device.
206: Sub-devices
207: .Pq Fl s
208: that are applied after will be attached to this device.
209: Device mode and parameters are determined from sub-devices
210: attached to it.
211: .It Fl j Ar flag
212: Control whether program channels are joined or expanded if
213: the number of channels requested by a program is not equal
214: to the device number of channels.
215: If the flag is
216: .Va off
217: then client channels are routed to the corresponding
218: device channel, possibly discarding channels not present in the device.
219: If the flag is
220: .Va on ,
221: then a single client channel may be sent on multiple device channels,
222: or multiple client channels may be sent to a single device channel.
223: For instance, this feature could be used for mono to stereo conversions.
224: The default is
225: .Ar on .
226: .It Fl L Ar addr
227: Specify a local network address
228: .Nm
229: should listen on;
230: .Nm
231: will listen on TCP port 11025+n, where n is the unit number
232: specified with
233: .Fl U .
234: Without this option,
235: .Nm
236: listens on the
237: .Ux Ns -domain
238: socket only, and is not reachable from any network.
239: If the option argument is
240: .Sq -
241: then
242: .Nm
243: will accept connections from any address.
244: As the communication is not secure, this
245: option is only suitable for local networks where all hosts
246: and users are trusted.
247: .It Fl m Ar mode
248: Set the sub-device mode.
249: Valid modes are
250: .Ar play ,
251: .Ar rec ,
252: and
253: .Ar mon ,
254: corresponding to playback, recording and monitoring.
255: A monitoring stream is a fake recording stream corresponding to
256: the mix of all playback streams.
257: Multiple modes can be specified, separated by commas,
258: but the same sub-device cannot be used for both recording and monitoring.
259: The default is
260: .Ar play , Ns Ar rec
261: (i.e. full-duplex).
1.3 ratchov 262: .It Fl Q Ar port
263: Specify an alternate MIDI port to use.
1.4 ratchov 264: If it doesn't work, the one given with the last
1.3 ratchov 265: .Fl Q
266: or
267: .Fl q
268: options will be used.
1.5 ! jmc 269: For instance, this allows a USB MIDI controller to be replaced without
1.3 ratchov 270: the need to restart programs using it.
1.1 ratchov 271: .It Fl q Ar port
272: Expose the given MIDI port.
273: This allows multiple programs to share the port.
274: .It Fl r Ar rate
275: Attempt to force the device to use this sample rate in Hertz.
276: The default is 48000.
277: .It Fl s Ar name
278: Add
279: .Ar name
280: to the list of sub-devices to expose.
281: This allows clients to use
282: .Nm
283: instead of the physical audio device for audio input and output
284: in order to share the physical device with other clients.
285: Defining multiple sub-devices allows splitting a physical audio device
286: into sub-devices having different properties (e.g. channel ranges).
287: The given
288: .Ar name
289: corresponds to the
290: .Dq option
291: part of the
292: .Xr sndio 7
293: device name string.
294: .It Fl t Ar mode
295: Select the way clients are controlled by MIDI Machine Control (MMC)
296: messages received by
297: .Nm .
298: If the mode is
299: .Va off
300: (the default), then programs are not affected by MMC messages.
301: If the mode is
302: .Va slave ,
303: then programs are started synchronously by MMC start messages;
304: additionally, the server clock is exposed as MIDI Time Code (MTC)
305: messages allowing MTC-capable software or hardware to be synchronized
306: to audio programs.
307: .It Fl U Ar unit
308: Unit number.
309: Each
310: .Nm
311: server instance has an unique unit number,
312: used in
313: .Xr sndio 7
314: device names.
315: The default is 0.
316: .It Fl v Ar volume
317: Software volume attenuation of playback.
318: The value must be between 1 and 127,
319: corresponding to \-42dB and \-0dB attenuation in 1/3dB steps.
320: Clients inherit this parameter.
321: Reducing the volume in advance allows a client's volume to stay independent
322: from the number of clients as long as their number is small enough.
323: 18 volume units (i.e. \-6dB attenuation) allows the number
324: of playback programs to be doubled.
325: The default is 118 i.e. \-3dB.
326: .It Fl w Ar flag
327: Control
328: .Nm
329: behaviour when the maximum volume of the hardware is reached
330: and a new program starts playing.
331: This happens only when volumes are not properly set using the
332: .Fl v
333: option.
334: If the flag is
335: .Va on ,
336: then the master volume is automatically adjusted to avoid clipping.
337: Using
338: .Va off
339: makes sense in the rare situation where all programs lower their volumes.
340: The default is
341: .Va on .
342: .It Fl z Ar nframes
343: The audio device block size in frames.
344: This is the number of frames between audio clock ticks,
345: i.e. the clock resolution.
346: If a sub-device is created with the
347: .Fl t
348: option, and MTC is used for synchronization, the clock
349: resolution must be 96, 100 or 120 ticks per second for maximum
350: accuracy.
351: For instance, 100 ticks per second at 48000Hz corresponds
352: to a 480 frame block size.
353: The default is 960 or half of the buffer size
354: .Pq Fl b ,
355: if the buffer size is set.
356: .El
357: .Pp
358: On the command line,
359: per-device parameters
360: .Pq Fl aberwz
361: must precede the device definition
362: .Pq Fl f ,
363: and per-sub-device parameters
364: .Pq Fl Ccjmtvx
365: must precede the sub-device definition
366: .Pq Fl s .
367: Sub-device definitions
368: .Pq Fl s
369: must follow the definition of the device
370: .Pq Fl f
371: to which they are attached.
372: .Pp
373: If no audio devices
374: .Pq Fl f
375: are specified,
376: settings are applied as if
377: the default device is specified.
378: If no sub-devices
379: .Pq Fl s
380: are specified for a device, a default sub-device is
381: created attached to it.
382: If a device
383: .Pq Fl f
384: is defined twice, both definitions are merged:
385: parameters of the first one are used but sub-devices
386: .Pq Fl s
387: of both definitions are created.
388: The default
389: .Xr sndio 7
390: device used by
391: .Nm
392: is
393: .Pa rsnd/0 ,
394: and the default sub-device exposed by
395: .Nm
396: is
397: .Pa snd/0 .
398: .Pp
399: If
400: .Nm
401: is sent
402: .Dv SIGINT
403: or
404: .Dv SIGTERM ,
405: it terminates.
1.3 ratchov 406: If
407: .Nm
408: is sent
409: .Dv SIGHUP ,
410: it reopens all audio devices and MIDI ports.
1.1 ratchov 411: .Pp
412: By default, when the program cannot accept
413: recorded data fast enough or cannot provide data to play fast enough,
414: the program is paused, i.e. samples that cannot be written are discarded
415: and samples that cannot be read are replaced by silence.
416: If a sub-device is created with the
417: .Fl t
418: option, then recorded samples are discarded,
419: but the same amount of silence will be written
420: once the program is unblocked, in order to reach the right position in time.
421: Similarly silence is played, but the same amount of samples will be discarded
422: once the program is unblocked.
423: This ensures proper synchronization between programs.
424: .Sh MIDI CONTROL
425: .Nm
426: creates a MIDI port with the same name as the exposed audio
427: sub-device to which MIDI programs can connect.
428: .Nm
429: exposes the audio device clock
430: and allows audio device properties to be controlled
431: through MIDI.
432: .Pp
433: A MIDI channel is assigned to each stream, and the volume
434: is changed using the standard volume controller (number 7).
435: Similarly, when the audio client changes its volume,
436: the same MIDI controller message is sent out; it can be used
437: for instance for monitoring or as feedback for motorized
438: faders.
439: .Pp
440: The master volume can be changed using the standard master volume
441: system exclusive message.
442: .Pp
443: Streams created with the
444: .Fl t
445: option are controlled by the following MMC messages:
446: .Bl -tag -width relocateXXX -offset indent
447: .It relocate
448: This message is ignored by audio
449: .Nm
450: clients, but the given time position is sent to MIDI ports as an MTC
451: .Dq "full frame"
452: message forcing all MTC-slaves to relocate to the given
453: position (see below).
454: .It start
455: Put all streams in starting mode.
456: In this mode,
457: .Nm
458: waits for all streams to become ready
459: to start, and then starts them synchronously.
460: Once started, new streams can be created
461: .Pq Nm sndiod
462: but they will be blocked
463: until the next stop-to-start transition.
464: .It stop
465: Put all streams in stopped mode (the default).
466: In this mode, any stream attempting to start playback or recording
467: is paused.
468: Client streams that are already
469: started are not affected until they stop and try to start again.
470: .El
471: .Pp
472: Streams created with the
473: .Fl t
474: option export the
475: .Nm
476: device clock using MTC, allowing non-audio
477: software or hardware to be synchronized to the audio stream.
478: Maximum accuracy is achieved when the number of blocks per
479: second is equal to one of the standard MTC clock rates (96, 100 and 120Hz).
480: The following sample rates
481: .Pq Fl r
482: and block sizes
483: .Pq Fl z
484: are recommended:
485: .Pp
486: .Bl -bullet -offset indent -compact
487: .It
488: 44100Hz, 441 frames (MTC rate is 100Hz)
489: .It
490: 48000Hz, 400 frames (MTC rate is 120Hz)
491: .It
492: 48000Hz, 480 frames (MTC rate is 100Hz)
493: .It
494: 48000Hz, 500 frames (MTC rate is 96Hz)
495: .El
496: .Pp
497: For instance, the following command will create two devices:
498: the default
499: .Va snd/0
500: and a MIDI-controlled
501: .Va snd/0.mmc :
502: .Bd -literal -offset indent
503: $ sndiod -r 48000 -z 400 -s default -t slave -s mmc
504: .Ed
505: .Pp
506: Streams connected to
507: .Va snd/0
508: behave normally, while streams connected to
509: .Va snd/0.mmc
510: wait for the MMC start signal and start synchronously.
511: Regardless of which device a stream is connected to,
512: its playback volume knob is exposed.
513: .Sh EXAMPLES
514: Start server using default parameters, creating an
515: additional sub-device for output to channels 2:3 only (rear speakers
516: on most cards), exposing the
517: .Pa snd/0
518: and
519: .Pa snd/0.rear
520: devices:
521: .Bd -literal -offset indent
522: $ sndiod -s default -c 2:3 -s rear
523: .Ed
524: .Pp
525: Start server creating the default sub-device with low volume and
526: an additional sub-device for high volume output, exposing the
527: .Pa snd/0
528: and
529: .Pa snd/0.max
530: devices:
531: .Bd -literal -offset indent
532: $ sndiod -v 65 -s default -v 127 -s max
533: .Ed
534: .Pp
535: Start server configuring the audio device to use
536: a 48kHz sample frequency, 240-frame block size,
537: and 2-block buffers.
538: The corresponding latency is 10ms, which is
539: the time it takes the sound to propagate 3.5 meters.
540: .Bd -literal -offset indent
541: $ sndiod -r 48000 -b 480 -z 240
542: .Ed
543: .Sh SEE ALSO
544: .Xr sndio 7
545: .Sh BUGS
546: Resampling is low quality; down-sampling especially should be avoided
547: when recording.
548: .Pp
549: Processing is done using 16-bit arithmetic,
550: thus samples with more than 16 bits are rounded.
551: 16 bits (i.e. 97dB dynamic) are largely enough for most applications though.
552: Processing precision can be increased to 24-bit at compilation time though.
553: .Pp
554: If
555: .Fl a Ar off
556: is used,
557: .Nm
558: creates sub-devices to expose first
559: and then opens the audio hardware on demand.
560: Technically, this allows
561: .Nm
562: to attempt to use one of the sub-devices it exposes as an audio device,
563: creating a deadlock.
564: There's nothing to prevent the user
565: from shooting himself in the foot by creating such a deadlock.
![[BACK]](/icons/back.gif){kind=icon}
Return to sndiod.8 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / sndiod