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[PATCH] player: support bypass for rate, bits, channel


From: Eric Wong
Subject: [PATCH] player: support bypass for rate, bits, channel
Date: Sat, 28 Sep 2013 07:11:26 +0000

This may be used to avoid automatic:

* resampling (rate)
* down/upmixing (channel)
* dither/truncation (bits)

Using any bypass mode means we can no longer guarantee gapless
playback for audio collections where rate, channel, or bits vary.
This can however be useful when CPU usage is too high.  This may
also be useful in audio engineering situations.
---
 Documentation/dtas-player_protocol.txt | 24 +++++++++++++------
 lib/dtas/format.rb                     |  8 +++++++
 lib/dtas/player.rb                     | 43 +++++++++++++++++++++++++++-------
 lib/dtas/player/client_handler.rb      | 15 +++++++++---
 test/test_format.rb                    |  5 ++++
 5 files changed, 77 insertions(+), 18 deletions(-)

diff --git a/Documentation/dtas-player_protocol.txt 
b/Documentation/dtas-player_protocol.txt
index 7fecec1..be1063a 100644
--- a/Documentation/dtas-player_protocol.txt
+++ b/Documentation/dtas-player_protocol.txt
@@ -111,20 +111,30 @@ Commands here should be alphabetized according to 
`LC_ALL=C sort'
   Changing this will affect the $SOXFMT and $ECAFMT environments passed
   to source and sink commands.  Changing this implies a "restart"
   Changing rate to 48000 is probably useful if you plan on playing to some
-  laptop sound cards.
+  laptop sound cards.  In all cases where "bypass" is supported, it
+  removes the guarantee of gapless playback as the audio device(s)
+  will likely need to be restarted.
 
-    + channels=UNSIGNED - (default: 2 (stereo)) - number of channels
-      to use internally.  sox will internally invoke the remix effect
-      when decoding.
+
+    + channels=(UNSIGNED|bypass) - (default: 2 (stereo)) - number of
+      channels to use internally.  sox will internally invoke the remix
+      effect when decoding.  This supports the value "bypass" (without
+      quotes) to avoid the automatic remix effect.  Using "bypass" mode
+      removes the guarantee of gapless playback, as the audio device will
+      likely need to be restarted, introducing an audible gap.
     + endian=(big|little|swap) - (default: native) - there is probably no
       point in changing this unless you output over a network sink to
       a machine of different endianess.
-    + bits=UNSIGNED - (default: implied from type) - sample precision (decoded)
+    + bits=(UNSIGNED|bypass) - (default: implied from type) - sample precision
+      (decoded)
       This may be pointless and removed in the future, since the sample
-      precision is implied from type.
-    + rate=UNSIGNED - (default: 44100) - sample rate of audio
+      precision is implied from type.  This supports the value of "bypass"
+      to avoid dither/truncation in later stages.
+    + rate=(UNSIGNED|bypass) - (default: 44100) - sample rate of audio
       Typical values of rate are 44100, 48000, 88200, 96000.  Not all
       DSP effects are compatible with all sampling rates/channels.
+      This supports the value of "bypass" as well to avoid introducing
+      software resamplers into the playback chain.
     + type=(s16|s24|s32|u16|u24|u32|f32|f64) - (default: s32)
       change the raw PCM format.  s32 currently offers the best performance
       when only sox/play are used.  f32 may offer better performance if
diff --git a/lib/dtas/format.rb b/lib/dtas/format.rb
index e9da16f..223d9c0 100644
--- a/lib/dtas/format.rb
+++ b/lib/dtas/format.rb
@@ -81,6 +81,14 @@ class DTAS::Format # :nodoc:
     ivars_to_hash(SIVS)
   end
 
+  def ==(other)
+    a = to_hash
+    b = other.to_hash
+    a["bits"] ||= bits_per_sample
+    b["bits"] ||= other.bits_per_sample
+    a == b
+  end
+
   # for the _decoded_ output
   def bits_per_sample
     return @bits if @bits
diff --git a/lib/dtas/player.rb b/lib/dtas/player.rb
index 273e56b..7567dfc 100644
--- a/lib/dtas/player.rb
+++ b/lib/dtas/player.rb
@@ -33,6 +33,7 @@ class DTAS::Player # :nodoc:
     @queue = [] # files for sources, or commands
     @paused = false
     @format = DTAS::Format.new
+    @bypass = [] # %w(rate bits channels) (not worth Hash overhead)
 
     @sinks = {} # { user-defined name => sink }
     @targets = [] # order matters
@@ -55,7 +56,10 @@ class DTAS::Player # :nodoc:
   end
 
   def wall(msg)
-    msg = xs(Array(msg))
+    __wall(xs(Array(msg)))
+  end
+
+  def __wall(msg)
     @watchers.delete_if do |io, _|
       if io.closed?
         true
@@ -84,6 +88,7 @@ class DTAS::Player # :nodoc:
 
     # Arrays
     rv["queue"] = @queue
+    rv["bypass"] = @bypass.sort!
 
     %w(rg sink_buf format).each do |k|
       rv[k] = instance_variable_get("@#{k}").to_hsh
@@ -123,7 +128,7 @@ class DTAS::Player # :nodoc:
         v = v["buffer_size"]
         @sink_buf.buffer_size = v
       end
-      %w(socket queue paused).each do |k|
+      %w(socket queue paused bypass).each do |k|
         v = hash[k] or next
         instance_variable_set("@#{k}", v)
       end
@@ -366,31 +371,46 @@ class DTAS::Player # :nodoc:
   def next_source(source_spec)
     @current = nil
     if source_spec
-      # restart sinks iff we were idle
-      spawn_sinks(source_spec) or return
-
       case source_spec
       when String
         pending = try_file(source_spec) or return
-        wall(%W(file #{pending.infile}))
+        msg = %W(file #{pending.infile})
       when Array
         pending = try_file(*source_spec) or return
-        wall(%W(file #{pending.infile} #{pending.offset_samples}s))
+        msg = %W(file #{pending.infile} #{pending.offset_samples}s)
       else
         pending = DTAS::Source::Cmd.new(source_spec["command"])
-        wall(%W(command #{pending.command_string}))
+        msg = %W(command #{pending.command_string})
+      end
+
+      unless @bypass.empty?
+        new_fmt = bypass_match!(@format.dup, pending.format)
+        if new_fmt != @format
+          stop_sinks # we may fail to start below
+          format_update!(new_fmt)
+        end
       end
 
+      # restart sinks iff we were idle
+      spawn_sinks(source_spec) or return
+
       dst = @sink_buf
       pending.dst_assoc(dst)
       pending.spawn(@format, @rg, out: dst.wr, in: "/dev/null")
       @current = pending
       @srv.wait_ctl(dst, :wait_readable)
+      wall(msg)
     else
       player_idle
     end
   end
 
+  def format_update!(fmt)
+    ary = fmt.to_hash.inject(%w(format)) { |m,(k,v)| v ? m << "#{k}=#{v}" : m }
+    @format = fmt
+    __wall(ary.join(' ')) # do not escape '='
+  end
+
   def player_idle
     stop_sinks if @sink_buf.inflight == 0
     @tl.reset unless @paused
@@ -457,4 +477,11 @@ class DTAS::Player # :nodoc:
     @sink_buf.close!
     @state_file.dump(self, true) if @state_file
   end
+
+  def bypass_match!(dst_fmt, src_fmt)
+    @bypass.each do |k|
+      dst_fmt.__send__("#{k}=", src_fmt.__send__(k))
+    end
+    dst_fmt
+  end
 end
diff --git a/lib/dtas/player/client_handler.rb 
b/lib/dtas/player/client_handler.rb
index 9c28486..a44c1b7 100644
--- a/lib/dtas/player/client_handler.rb
+++ b/lib/dtas/player/client_handler.rb
@@ -295,6 +295,7 @@ module DTAS::Player::ClientHandler # :nodoc:
     end
     tmp["current_inflight"] = @sink_buf.inflight
     tmp["format"] = @format.to_hash.delete_if { |_,v| v.nil? }
+    tmp["bypass"] = @bypass.sort!
     tmp["paused"] = @paused
     rg = @rg.to_hsh
     tmp["rg"] = rg unless rg.empty?
@@ -402,20 +403,28 @@ module DTAS::Player::ClientHandler # :nodoc:
         new_fmt.valid_type?(v) or return io.emit("ERR invalid file type")
         new_fmt.type = v
       when "channels", "bits", "rate"
-        rv = set_uint(io, kv, v, false) { |u| new_fmt.__send__("#{k}=", u) }
-        rv == true or return rv
+        case v
+        when "bypass"
+          @bypass << k unless @bypass.include?(k)
+        else
+          rv = set_uint(io, kv, v, false) { |u| new_fmt.__send__("#{k}=", u) }
+          rv == true or return rv
+          @bypass.delete(k)
+        end
       when "endian"
         new_fmt.valid_endian?(v) or return io.emit("ERR invalid endian")
         new_fmt.endian = v
       end
     end
 
+    bypass_match!(new_fmt, @current.format) if @current
+
     if new_fmt != @format
       restart_pipeline # calls __current_requeue
 
       # we must assign this after __current_requeue since __current_requeue
       # relies on the old @format for calculation
-      @format = new_fmt
+      format_update!(new_fmt)
     end
     io.emit("OK")
   end
diff --git a/test/test_format.rb b/test/test_format.rb
index f251e6b..0441d9a 100644
--- a/test/test_format.rb
+++ b/test/test_format.rb
@@ -12,6 +12,11 @@ class TestFormat < Testcase
     assert_equal({}, hash)
   end
 
+  def test_equal
+    fmt = DTAS::Format.new
+    assert_equal fmt, fmt.dup
+  end
+
   def test_nonstandard
     fmt = DTAS::Format.new
     fmt.type = "s16"
-- 
1.8.4




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