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Support an absolute end position for trim effect instead of only
an offset from trim begin.

--- a/ChangeLog

+++ b/ChangeLog

@@ -54,6 +54,8 @@

   o Enable LADSPA effects on all platforms without any external

     dependencies.  Mainly useful for Linux, Windows and OS X which have

     binaries readily available. (cbagwell)

+  o Support specifying an absolute end location for trim effect instead

+    only an offset from trim begin location. (Ulrich Klauer)

 Other new features:

--- a/sox.1

+++ b/sox.1

@@ -3925,7 +3925,7 @@

 .I depth

 (default 40).

 .TP

-\fBtrim \fIstart\fR [\fIlength\fR]

+\fBtrim \fIstart\fR [\fIlength\fR\^|\^\fB=\fIend\fR]

 Trim can trim off unwanted audio from the beginning and end of the

 audio.  Audio is not sent to the output stream until

 the \fIstart\fR location is reached.

@@ -3932,16 +3932,17 @@

 .SP

 The optional \fIlength\fR parameter gives the length of audio to output

 after the \fIstart\fR sample and is thus used to trim off the end of the

-audio.  Using a value of 0 for the \fIstart\fR parameter will allow

-trimming off the end only.

+audio.  Alternatively, an absolute end location can be given by

+preceding it with an equals sign.  Using a value of 0 for the \fIstart\fR

+parameter will allow trimming off the end only.

 .SP

-Both options can be specified using either an amount of time or an

+Both parameters can be specified using either an amount of time or an

 exact count of samples.  The format for specifying lengths in time is

 hh:mm:ss.frac.  A start value of 1:30\*d5 will not start until 1 minute,

 thirty and \(12 seconds into the audio.  The format for specifying

 sample counts is the number of samples with the letter `s' appended to

-it.  A value of 8000s will wait until 8000 samples are read before

-starting to process audio.

+it.  A value of 8000s for the \fIstart\fR parameter will wait until

+8000 samples are read before starting to process audio.

 .TP

 \fBvad \fR[\fIoptions\fR]

 Voice Activity Detector.  Attempts to trim silence and quiet

--- a/src/trim.c

+++ b/src/trim.c

@@ -12,7 +12,8 @@

 typedef struct {

     /* options here */

     char *start_str;

-    char *length_str;

+    char *end_str;

+    sox_bool end_is_absolute;

     /* options converted to values */

     size_t start;

@@ -28,6 +29,7 @@

  */

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

 {

+    char *end;

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

   --argc, ++argv;

@@ -36,10 +38,15 @@

      */

     switch (argc) {

         case 2:

-            trim->length_str = lsx_malloc(strlen(argv[1])+1);

-            strcpy(trim->length_str,argv[1]);

+            end = argv[1];

+            if (*end == '=') {

+                trim->end_is_absolute = sox_true;

+                end++;

+            } else trim->end_is_absolute = sox_false;

+            trim->end_str = lsx_malloc(strlen(end)+1);

+            strcpy(trim->end_str, end);

             /* Do a dummy parse to see if it will fail */

-            if (lsx_parsesamples(0., trim->length_str, &trim->length, 't') == NULL)

+            if (lsx_parsesamples(0., trim->end_str, &trim->length, 't') == NULL)

               return lsx_usage(effp);

         case 1:

             trim->start_str = lsx_malloc(strlen(argv[0])+1);

@@ -65,19 +72,29 @@

     if (lsx_parsesamples(effp->in_signal.rate, trim->start_str,

                         &trim->start, 't') == NULL)

       return lsx_usage(effp);

-    /* Account for # of channels */

-    trim->start *= effp->in_signal.channels;

-    if (trim->length_str)

+    if (trim->end_str)

     {

-        if (lsx_parsesamples(effp->in_signal.rate, trim->length_str,

+        if (lsx_parsesamples(effp->in_signal.rate, trim->end_str,

                     &trim->length, 't') == NULL)

           return lsx_usage(effp);

+        if (trim->end_is_absolute) {

+            if (trim->length < trim->start) {

+                lsx_warn("end earlier than start");

+                trim->length = 0;

+                  /* with trim->end_str != NULL, this really means zero */

+            } else

+                trim->length -= trim->start;

+        }

     }

     else

         trim->length = 0;

+          /* with trim->end_str == NULL, this means indefinite length */

+    lsx_debug("start at %lus, length %lu", trim->start, trim->length);

+

     /* Account for # of channels */

+    trim->start *= effp->in_signal.channels;

     trim->length *= effp->in_signal.channels;

     trim->index = 0;

@@ -130,7 +147,7 @@

     } /* !trimmed */

     if (trim->trimmed || start_trim) {

-        if (trim->length_str && ((trim->trimmed+done) >= trim->length)) {

+        if (trim->end_str && ((trim->trimmed+done) >= trim->length)) {

             /* Since we know the end is in this block, we set done

              * to the desired length less the amount already read.

              */

@@ -153,7 +170,7 @@

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

     free(trim->start_str);

-    free(trim->length_str);

+    free(trim->end_str);

     return (SOX_SUCCESS);

 }

@@ -173,7 +190,7 @@

 const sox_effect_handler_t *lsx_trim_effect_fn(void)

 {

   static sox_effect_handler_t handler = {

-    "trim", "start [length]", SOX_EFF_MCHAN | SOX_EFF_LENGTH | SOX_EFF_MODIFY,

+    "trim", "start [length|=end]", SOX_EFF_MCHAN | SOX_EFF_LENGTH | SOX_EFF_MODIFY,

     sox_trim_getopts, sox_trim_start, sox_trim_flow,

     NULL, NULL, lsx_kill, sizeof(priv_t)

   };