[PATCH 3/3] splitfx: support tshift directive

[Eric Wong]

This directive is useful for cutting sections of audio out in
addition to making it easier to share track offsets between
different recordings of the same source.
---
 Documentation/dtas-splitfx.pod | 14 ++++++++++++++
 lib/dtas/splitfx.rb            | 20 +++++++++++++++++---
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/Documentation/dtas-splitfx.pod b/Documentation/dtas-splitfx.pod
index 6f8d9ed..88179d7 100644
--- a/Documentation/dtas-splitfx.pod
+++ b/Documentation/dtas-splitfx.pod
@@ -173,6 +173,20 @@ any tracks written to the filesystem, including those 
using the L</--filter>
 switch.   These environment variables are intended to affect the specified
 L</command> or default L<sox(1)> invocation.
 
+=item tshift TIME
+
+Increment subsequent time stamps for L</t>, L</skip>, and L</stop>
+directives by the specified TIME offset.  TIME can be prefixed by
+C<+=> or C<-=> to adjust the existing C<tshift> value.  Negative
+values can be specified by prefixing with C<-> for a backwards
+time shift.
+
+This directive is useful for working with multiple recordings of the
+same source and cutting a section from the middle of a recording after
+initial tracking is done.
+
+Default: 0
+
 =item skip TIME - skip a segment starting at TIME
 
 "skip" segments are
diff --git a/lib/dtas/splitfx.rb b/lib/dtas/splitfx.rb
index 1150ee0..b94f54b 100644
--- a/lib/dtas/splitfx.rb
+++ b/lib/dtas/splitfx.rb
@@ -66,6 +66,7 @@ def commit(advance_track_samples)
   # $CHANNELS (input)
   # $BITS_PER_SAMPLE (input)
   def initialize
+    @tshift = 0
     @env = {}
     @comments = {}
     @track_start = 1
@@ -290,7 +291,7 @@ def parse_track(argv)
       start_time = argv.shift
       title = argv.shift
       t = T.new
-      t.tbeg = @t2s.call(start_time)
+      t.tbeg = @t2s.call(start_time) + @tshift
       t.comments = @comments.dup
       title.valid_encoding? or warn "#{title.inspect} encoding invalid"
       t.comments["TITLE"] = title
@@ -311,11 +312,24 @@ def parse_track(argv)
 
       prev = @tracks.last and prev.commit(t.tbeg)
       @tracks << t
+    when 'tshift'
+      tshift = argv.shift
+      argv.empty? or raise ArgumentError, 'tshift does not take extra args'
+      if tshift.sub!(/\A-=/, '')
+        @tshift = @tshift - @t2s.call(tshift)
+      elsif tshift.sub!(/\A\+=/, '')
+        @tshift = @tshift + @t2s.call(tshift)
+      elsif tshift.sub!(/\A-/, '')
+        @tshift = -@t2s.call(tshift)
+      else
+        tshift.sub!(/\A\+/, '')
+        @tshift = @t2s.call(tshift)
+      end
     when "skip"
       stop_time = argv.shift
       argv.empty? or raise ArgumentError, "skip does not take extra args"
       s = Skip.new
-      s.tbeg = @t2s.call(stop_time)
+      s.tbeg = @t2s.call(stop_time) + @tshift
       # s.comments = {}
       # s.env = {}
       prev = @tracks.last or raise ArgumentError, "no tracks to skip"
@@ -324,7 +338,7 @@ def parse_track(argv)
     when "stop"
       stop_time = argv.shift
       argv.empty? or raise ArgumentError, "stop does not take extra args"
-      samples = @t2s.call(stop_time)
+      samples = @t2s.call(stop_time) + @tshift
       prev = @tracks.last and prev.commit(samples)
     else
       raise ArgumentError, "unknown command: #{xs(cmd)}"