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Let some effects calculate expected output length

For certain effects (see below) that change audio length
(SOX_EFF_LENGTH), calculate the expected output length for propagation
down the effects chain. This makes it possible, e.g., to use a
fade-out later without specifying an explicit end position.

This commit takes care of the following effects: delay, fade, pad,
repeat, speed, synth, trim. It would probably be possible to do the
same for more effects: chorus, echo, echos, noisered, phaser, stretch,
tempo. For these three effects, however, calculating the output length
beforehand is impossible as it depends on the input audio: silence,
splice, vad.

--- a/src/delay.c

+++ b/src/delay.c

@@ -84,8 +84,11 @@

     p->buffer_size = temp;

   }

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

-  if (effp->flow == 0)

+  if (effp->flow == 0) {

+    effp->out_signal.length = effp->in_signal.length ?

+       effp->in_signal.length + max_delay * effp->in_signal.channels : 0;

     lsx_debug("extending audio by %" PRIu64 " 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));

--- a/src/fade.c

+++ b/src/fade.c

@@ -187,6 +187,9 @@

         fade->out_start == fade->out_stop)

       return SOX_EFF_NULL;

+    effp->out_signal.length = truncate ?

+        fade->out_stop * effp->in_signal.channels : effp->in_signal.length;

+

     return SOX_SUCCESS;

 }

--- a/src/pad.c

+++ b/src/pad.c

@@ -76,7 +76,29 @@

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

   unsigned i;

-  parse(effp, 0, effp->in_signal.rate); /* Re-parse now rate is known */

+  /* Re-parse now rate is known */

+  if (parse(effp, 0, effp->in_signal.rate) != SOX_SUCCESS)

+    return SOX_EOF;

+

+  if ((effp->out_signal.length = effp->in_signal.length) != 0) {

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

+      effp->out_signal.length +=

+        p->pads[i].pad * effp->in_signal.channels;

+

+    /* Check that the last pad position (except for "at the end")

+       is within bounds. */

+    i = p->npads;

+    if (i > 0 && p->pads[i-1].start == UINT64_MAX)

+      i--;

+    if (i > 0 &&

+        p->pads[i-1].start * effp->in_signal.channels

+          > effp->in_signal.length)

+    {

+      lsx_fail("pad position after end of audio");

+      return SOX_EOF;

+    }

+  }

+

   p->in_pos = p->pad_pos = p->pads_pos = 0;

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

     if (p->pads[i].pad)

--- a/src/repeat.c

+++ b/src/repeat.c

@@ -45,6 +45,7 @@

   }

   p->num_samples = p->remaining_samples = 0;

   p->remaining_repeats = p->num_repeats;

+  effp->out_signal.length = effp->in_signal.length * (p->num_repeats + 1);

   return SOX_SUCCESS;

 }

--- a/src/speed.c

+++ b/src/speed.c

@@ -56,6 +56,10 @@

     return SOX_EFF_NULL;

   effp->out_signal.rate = effp->in_signal.rate * p->factor;

+

+  effp->out_signal.length = effp->in_signal.length;

+    /* audio length if measured in samples doesn't change */

+

   return SOX_SUCCESS;

 }

--- a/src/synth.c

+++ b/src/synth.c

@@ -415,9 +415,11 @@

   p->samples_done = 0;

-  if (p->length_str)

+  if (p->length_str) {

     if (lsx_parsesamples(effp->in_signal.rate, p->length_str, &p->samples_to_do, 't') == NULL)

       return lsx_usage(effp);

+  } else

+    p->samples_to_do = effp->in_signal.length / effp->in_signal.channels;

   p->number_of_channels = effp->in_signal.channels;

   p->channels = lsx_calloc(p->number_of_channels, sizeof(*p->channels));

@@ -523,6 +525,7 @@

   }

   p->gain = 1;

   effp->out_signal.mult = p->no_headroom? NULL : &p->gain;

+  effp->out_signal.length = p->samples_to_do * effp->out_signal.channels;

   return SOX_SUCCESS;

 }

--- a/src/trim.c

+++ b/src/trim.c

@@ -107,7 +107,20 @@

     trim->index = 0;

     trim->trimmed = 0;

+    if (effp->in_signal.length) {

+      if (trim->start >= effp->in_signal.length) {

+        lsx_fail("start position after end of file");

+        return SOX_EOF;

+      } else if (trim->start + trim->length >= effp->in_signal.length) {

+        lsx_fail("end position after end of file");

+        return SOX_EOF;

+      }

+    }

+

     effp->out_signal.length = trim->length;

+    if (!effp->out_signal.length && effp->in_signal.length > trim->start)

+        effp->out_signal.length = effp->in_signal.length - trim->start;

+

     return (SOX_SUCCESS);

 }