Add support for channel transforms.

media/base/channel_mixer_unittest.cc

Index: media/base/channel_mixer_unittest.cc
diff --git a/media/base/channel_mixer_unittest.cc b/media/base/channel_mixer_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ce7db0a4870781c39a4c590946ab1356c0497292
--- /dev/null
+++ b/media/base/channel_mixer_unittest.cc
@@ -0,0 +1,32 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/base/audio_bus.h"
+#include "media/base/channel_mixer.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace media {
+
+// Test flush resets the internal state properly.
+TEST(ChannelMixerTest, Construction) {
+  static const int kFrames = 16;
+
+  for (ChannelLayout input_layout = CHANNEL_LAYOUT_MONO;
+       input_layout < CHANNEL_LAYOUT_MAX; input_layout++) {
+    for (ChannelLayout output_layout = CHANNEL_LAYOUT_MONO;
+         output_layout < CHANNEL_LAYOUT_STEREO_DOWNMIX; output_layout++) {
+      ChannelMixer mixer(input_layout, output_layout);

[scherkus (not reviewing), 2012/10/18 01:30:39]

should consider using SCOPED_TRACE() to document the combination of input+output
in case of a failure

either that or parameterized tests, but that seems like a lot of work for little
benefit

[DaleCurtis, 2012/10/18 05:22:04]

Done.

+      scoped_ptr<AudioBus> input_bus = AudioBus::Create(
+          ChannelLayoutToChannelCount(input_layout), kFrames);
+      scoped_ptr<AudioBus> output_bus = AudioBus::Create(
+          ChannelLayoutToChannelCount(output_layout), kFrames);
+      for(int ch = 0; ch < input_bus->channels(); ++ch)
+        std::fill(input_bus->channel(ch), input_bus->channel(ch) + kFrames, 1);
+
+      mixer.Rematrix(input_bus.get(), output_bus.get());

[scherkus (not reviewing), 2012/10/18 01:30:39]

what exactly are we testing?

[DaleCurtis, 2012/10/18 01:56:44]

Just that construction of all layouts is possible (DCHECKS will explode
otherwise) at the moment. I haven't thought of a good automated test for this
yet, other than maybe that some input exists in the output? Ideas welcome.

[scherkus (not reviewing), 2012/10/18 02:24:03]

How about naming this "AllLayoutCombinations" instead of "Construction"?

The only idea I have is 3 canned sanity checking tests that cover the three
different mixing cases chris pointed out (mono -> stereo mix using scale=1,
stereo -> mono using scale=1/2, surround mix using scale=1/sqrt(2)). They don't
have to be fancy.

[DaleCurtis, 2012/10/18 05:22:04]

Done.

+    }
+  }
+}
+
+}  // namespace media