alsaloop: added option prateshift for PLAYSHIFT ctl elem used in PLAYSHIFT

If snd-aloop device is on playback side, the required sync mode is
PLAYSHIFT. That means Loopback ctl elem "PCM Rate Shift 100000" of the
corresponding capture side of the Loopback pipe must be controlled (by
a reciprocal).

ASCII name of the playback rate shift ctl elem is specified with newly
added option -x/--prateshift, e.g.:
  -P hw:Loopback,0 -S playshift \
  -x iface=PCM,name='PCM Rate Shift 100000',device=1

Signed-off-by: Pavel Hofman <pavel.hofman@ivitera.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

alsaloop/alsaloop.1

@@ -57,6 +57,11 @@ Use given CTL device for playback.
 
 Use given CTL device for capture.
 
+.TP
+\fI\-x <ctl_ascii_name>\fP | \fI\-\-prateshift=<ctl_ascii_name>\fP
+
+Specify ctl ascii name for playshift sync mode (see the Examples section).
+
 .TP
 \fI\-l <latency>\fP | \fI\-\-latency=<frames>\fP
 
@@ -195,10 +200,12 @@ Verbose xrun profiling.
 Set process wake timeout.
 
 .SH EXAMPLES
-
+.nf
-.TP
 \fBalsaloop \-C hw:0,0 \-P hw:1,0 \-t 50000\fR
 
+\fBalsaloop \-C hw:soundcard,0 \-P hw:Loopback,0 \-t 50000 \-S playshift \\
+\-x iface=PCM,name='PCM Rate Shift 100000',device=1\fR
+.ne
 .SH BUGS
 None known.
 .SH AUTHOR

alsaloop/alsaloop.c

@@ -175,6 +175,7 @@ void help(void)
 "-C,--cdevice   capture device\n"
 "-X,--pctl      playback ctl device\n"
 "-Y,--cctl      capture ctl device\n"
+"-x,--prateshift playback 'PCM Rate Shift 100000' ascii ctl name\n"
 "-l,--latency   requested latency in frames\n"
 "-t,--tlatency  requested latency in usec (1/1000000sec)\n"
 "-f,--format    sample format\n"
@@ -362,6 +363,7 @@ static int parse_config(int argc, char *argv[], snd_output_t *output,
 		{"cdevice", 1, NULL, 'C'},
 		{"pctl", 1, NULL, 'X'},
 		{"cctl", 1, NULL, 'Y'},
+		{"prateshift", 1, NULL, 'x'},
 		{"latency", 1, NULL, 'l'},
 		{"tlatency", 1, NULL, 't'},
 		{"format", 1, NULL, 'f'},
@@ -391,6 +393,7 @@ static int parse_config(int argc, char *argv[], snd_output_t *output,
 	char *arg_cdevice = NULL;
 	char *arg_pctl = NULL;
 	char *arg_cctl = NULL;
+	char *arg_prateshift = NULL;
 	unsigned int arg_latency_req = 0;
 	unsigned int arg_latency_reqtime = 10000;
 	snd_pcm_format_t arg_format = SND_PCM_FORMAT_S16_LE;
@@ -420,7 +423,7 @@ static int parse_config(int argc, char *argv[], snd_output_t *output,
 	while (1) {
 		int c;
 		if ((c = getopt_long(argc, argv,
-				"hdg:P:C:X:Y:l:t:F:f:c:r:s:benvA:S:a:m:T:O:w:UW:z",
+				"hdg:P:C:X:Y:x:l:t:F:f:c:r:s:benvA:S:a:m:T:O:w:UW:z",
 				long_option, NULL)) < 0)
 			break;
 		switch (c) {
@@ -446,6 +449,9 @@ static int parse_config(int argc, char *argv[], snd_output_t *output,
 		case 'Y':
 			arg_cctl = strdup(optarg);
 			break;
+		case 'x':
+			arg_prateshift = strdup(optarg);
+			break;
 		case 'l':
 			err = atoi(optarg);
 			arg_latency_req = err >= 4 ? err : 4;
@@ -627,6 +633,9 @@ static int parse_config(int argc, char *argv[], snd_output_t *output,
 			logit(LOG_CRIT, "Unable to add ossmixer controls.\n");
 			exit(EXIT_FAILURE);
 		}
+		if (arg_prateshift)
+			play->prateshift_name = arg_prateshift;
+
 #ifdef USE_SAMPLERATE
 		loop->src_enable = arg_samplerate > 0;
 		if (loop->src_enable)

alsaloop/alsaloop.h

@@ -127,6 +127,7 @@ struct loopback_handle {
 	snd_ctl_elem_value_t *ctl_format;
 	snd_ctl_elem_value_t *ctl_rate;
 	snd_ctl_elem_value_t *ctl_channels;
+	char *prateshift_name; /* ascii name for the playback rate shift ctl elem */
 };
 
 struct loopback {

alsaloop/pcmjob.c

@@ -1101,7 +1101,8 @@ void update_pitch(struct loopback *loop)
 #endif
 	}
 	else if (loop->sync == SYNC_TYPE_PLAYRATESHIFT) {
-		set_rate_shift(loop->play, pitch);
+		// pitch is capture-based, playback side requires reciprocal
+		set_rate_shift(loop->play, 1 / pitch);
 #ifdef USE_SAMPLERATE
 		if (loop->use_samplerate) {
 			loop->src_data.src_ratio = 
@@ -1172,32 +1173,57 @@ static int get_channels(struct loopback_handle *lhandle)
 	return snd_ctl_elem_value_get_integer(lhandle->ctl_channels, 0);
 }
 
-static void openctl_elem(struct loopback_handle *lhandle,
+static int openctl_elem_id(struct loopback_handle *lhandle, snd_ctl_elem_id_t *id,
-			 int device, int subdevice,
+		snd_ctl_elem_value_t **elem)
-			 const char *name,
-			 snd_ctl_elem_value_t **elem)
 {
 	int err;
 
 	if (snd_ctl_elem_value_malloc(elem) < 0) {
 		*elem = NULL;
-	} else {
+		return -ENOMEM;
-		snd_ctl_elem_value_set_interface(*elem,
-						 SND_CTL_ELEM_IFACE_PCM);
-		snd_ctl_elem_value_set_device(*elem, device);
-		snd_ctl_elem_value_set_subdevice(*elem, subdevice);
-		snd_ctl_elem_value_set_name(*elem, name);
-		err = snd_ctl_elem_read(lhandle->ctl, *elem);
-		if (err < 0) {
-			snd_ctl_elem_value_free(*elem);
-			*elem = NULL;
-		} else {
-			if (verbose)
-				snd_output_printf(lhandle->loopback->output,
-						"Opened PCM element %s of %s, device %d, subdevice %d\n",
-						name, snd_ctl_name(lhandle->ctl), device, subdevice);
-		}
 	}
+	snd_ctl_elem_value_set_id(*elem, id);
+	snd_ctl_elem_value_set_interface(*elem, SND_CTL_ELEM_IFACE_PCM);
+	err = snd_ctl_elem_read(lhandle->ctl, *elem);
+	if (err < 0) {
+		snd_ctl_elem_value_free(*elem);
+		*elem = NULL;
+		return err;
+	} else {
+		snd_output_printf(lhandle->loopback->output,
+				"Opened PCM element %s of %s, device %d, subdevice %d\n",
+				snd_ctl_elem_id_get_name(id), snd_ctl_name(lhandle->ctl),
+				snd_ctl_elem_id_get_device(id),
+				snd_ctl_elem_id_get_subdevice(id));
+		return 0;
+	}
+}
+
+static int openctl_elem(struct loopback_handle *lhandle,
+			 int device, int subdevice,
+			 const char *name,
+			 snd_ctl_elem_value_t **elem)
+{
+	snd_ctl_elem_id_t *id;
+
+	snd_ctl_elem_id_alloca(&id);
+	snd_ctl_elem_id_set_device(id, device);
+	snd_ctl_elem_id_set_subdevice(id, subdevice);
+	snd_ctl_elem_id_set_name(id, name);
+	return openctl_elem_id(lhandle, id, elem);
+}
+
+static int openctl_elem_ascii(struct loopback_handle *lhandle, char *ascii_name,
+		snd_ctl_elem_value_t **elem)
+{
+	snd_ctl_elem_id_t *id;
+
+	snd_ctl_elem_id_alloca(&id);
+	if (snd_ctl_ascii_elem_id_parse(id, ascii_name)) {
+		fprintf(stderr, "Wrong control identifier: %s\n", ascii_name);
+		return -EINVAL;
+	}
+	return openctl_elem_id(lhandle, id, elem);
 }
 
 static int openctl(struct loopback_handle *lhandle, int device, int subdevice)
@@ -1206,10 +1232,21 @@ static int openctl(struct loopback_handle *lhandle, int device, int subdevice)
 
 	lhandle->ctl_rate_shift = NULL;
 	if (lhandle->loopback->play == lhandle) {
+		// play only
+		if (lhandle->prateshift_name) {
+			err = openctl_elem_ascii(lhandle, lhandle->prateshift_name,
+					&lhandle->ctl_rate_shift);
+			if (err < 0) {
+				logit(LOG_CRIT, "Unable to open playback PCM Rate Shift elem '%s'.\n",
+						lhandle->prateshift_name);
+				exit(EXIT_FAILURE);
+			}
+		}
 		if (lhandle->loopback->controls)
 			goto __events;
 		return 0;
 	}
+	// capture only
 	openctl_elem(lhandle, device, subdevice, "PCM Notify",
 			&lhandle->ctl_notify);
 	openctl_elem(lhandle, device, subdevice, "PCM Rate Shift 100000",