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delay effect: Allow a delay to be more than the input length

The delay effect would fail ("drained asymmetrically!") when a specified
delay was more than the input length, e.g.
  play stereo.wav trim 0 1 delay 0 2
In this special case, drain() will now output additional silence such that
the specified delay is reached and all channels end simultaneously.

This resolves bug #3055399.

--- a/ChangeLog

+++ b/ChangeLog

@@ -41,6 +41,8 @@

   o Effect chain can now be unlimitted in length. (Ulrich Klauer)

   o Fix newfile/restart effects when merging or mixing files. (Ulrich Klauer)

   o Fix crashes in compand and mcompand effects. [3420893] (Ulrich Klauer)

+  o Let the delay effect gracefully handle the special case that a delay can

+    be more than the input length. [3055399] (Ulrich Klauer)

 Misc:

--- a/src/delay.c

+++ b/src/delay.c

@@ -21,8 +21,9 @@

 typedef struct {

   size_t argc;

   char * * argv, * max_arg;

-  size_t delay, pad, buffer_size, buffer_index;

+  size_t delay, pre_pad, pad, buffer_size, buffer_index;

   sox_sample_t * buffer;

+  sox_bool drain_started;

 } priv_t;

 static int lsx_kill(sox_effect_t * effp)

@@ -43,7 +44,8 @@

   unsigned i;

   --argc, ++argv;

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

+  p->argc = argc;

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

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

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

     if (!next || *next) {

@@ -75,9 +77,12 @@

   if (effp->flow < p->argc)

     lsx_parsesamples(effp->in_signal.rate, p->argv[effp->flow], &p->buffer_size, 't');

   lsx_parsesamples(effp->in_signal.rate, p->max_arg, &max_delay, 't');

-  p->buffer_index = p->delay = 0;

+  if (effp->flow == 0)

+    lsx_debug("extending audio by %" FMT_size_t " samples", max_delay);

+  p->buffer_index = p->delay = p->pre_pad = 0;

   p->pad = max_delay - p->buffer_size;

   p->buffer = lsx_malloc(p->buffer_size * sizeof(*p->buffer));

+  p->drain_started = sox_false;

   return SOX_SUCCESS;

 }

@@ -105,8 +110,18 @@

 static int drain(sox_effect_t * effp, sox_sample_t * obuf, size_t * osamp)

 {

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

-  size_t len = *osamp = min(p->delay + p->pad, *osamp);

+  size_t len;

+  if (! p->drain_started) {

+    p->drain_started = sox_true;

+    p->pre_pad = p->buffer_size - p->delay;

+      /* If the input was too short to fill the buffer completely,

+         flow() has not yet output enough silence to reach the

+         desired delay. */

+  }

+  len = *osamp = min(p->pre_pad + p->delay + p->pad, *osamp);

+  for (; p->pre_pad && len; --p->pre_pad, --len)

+    *obuf++ = 0;

   for (; p->delay && len; --p->delay, --len) {

     *obuf++ = p->buffer[p->buffer_index++];

     p->buffer_index %= p->buffer_size;