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delay: use lsx_parseposition

Use the new lsx_parseposition function for the delay effect and update
the documentation accordingly.

--- a/sox.1

+++ b/sox.1

@@ -1937,14 +1937,15 @@

 .SP

 See also the \fBbass\fR and \fBtreble\fR shelving equalisation effects.

 .TP

-\fBdelay\fR {\fItime\fR}

-Delay one or more audio channels by the given \fItime\fR (a time

-specification).

+\fBdelay\fR {\fIposition(=)\fR}

+Delay one or more audio channels such that they start at the given

+\fIposition\fR.

 For example,

-.B delay 1\*d5 0 3000s

-delays the first channel by 1\*d5 seconds, the third channel by 3000

-samples, and leaves the second channel (and any other channels that may be

-present) un-delayed.

+.B delay 1\*d5 +1 3000s

+delays the first channel by 1\*d5 seconds, the second channel by 2\*d5

+seconds (one second more than the previous channel), the third channel

+by 3000 samples, and leaves any other channels that may be

+present un-delayed.

 The following (one long) command plays a chime sound:

 .EX

 .ne 3

--- a/src/delay.c

+++ b/src/delay.c

@@ -43,7 +43,6 @@

 static int create(sox_effect_t * effp, int argc, char * * argv)

 {

   priv_t * p = (priv_t *)effp->priv;

-  uint64_t dummy;

   unsigned i;

   --argc, ++argv;

@@ -51,7 +50,7 @@

   p->args = lsx_calloc(p->argc, sizeof(*p->args));

   p->max_delay = lsx_malloc(sizeof(*p->max_delay));

   for (i = 0; i < p->argc; ++i) {

-    char const * next = lsx_parsesamples(1e5, p->args[i].str = lsx_strdup(argv[i]), &dummy, 't');

+    char const * next = lsx_parseposition(0., p->args[i].str = lsx_strdup(argv[i]), NULL, (uint64_t)0, (uint64_t)0, '=');

     if (!next || *next) {

       lsx_kill(effp);

       return lsx_usage(effp);

@@ -70,7 +69,9 @@

 static int start(sox_effect_t * effp)

 {

   priv_t * p = (priv_t *)effp->priv;

-  uint64_t max_delay = 0, delay;

+  uint64_t max_delay = 0, last_seen = 0, delay;

+  uint64_t in_length = effp->in_signal.length != SOX_UNKNOWN_LEN ?

+    effp->in_signal.length / effp->in_signal.channels : SOX_UNKNOWN_LEN;

   if (effp->flow == 0) {

     unsigned i;

@@ -79,8 +80,11 @@

       return SOX_EOF;

     }

     for (i = 0; i < p->argc; ++i) {

-      lsx_parsesamples(effp->in_signal.rate, p->args[i].str, &delay, 't');

-      p->args[i].delay = delay;

+      if (!lsx_parseposition(effp->in_signal.rate, p->args[i].str, &delay, last_seen, in_length, '=') || delay == SOX_UNKNOWN_LEN) {

+        lsx_fail("Position relative to end of audio specified, but audio length is unknown");

+        return SOX_EOF;

+      }

+      p->args[i].delay = last_seen = delay;

       if (delay > max_delay) {

         max_delay = delay;

       }

@@ -152,7 +156,7 @@

 sox_effect_handler_t const * lsx_delay_effect_fn(void)

 {

   static sox_effect_handler_t handler = {

-    "delay", "{length}", SOX_EFF_LENGTH | SOX_EFF_MODIFY,

+    "delay", "{position}", SOX_EFF_LENGTH | SOX_EFF_MODIFY,

     create, start, flow, drain, stop, lsx_kill, sizeof(priv_t)

   };

   return &handler;