Make sure AudioBufferConverter uses aligned AudioBus channels.

SIMD requires aligned loads or it'll crash.

BUG=357840
TEST=new unittest. played video back in crashes.
R=rileya@chromium.org, scherkus@chromium.org
TBR=scherkus

Review URL: https://codereview.chromium.org/217923002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@260336 0039d316-1c4b-4281-b951-d872f2087c98

media/base/audio_buffer_converter.cc

@@ -199,10 +199,13 @@ void AudioBufferConverter::ConvertIfPossible() {
   // The AudioConverter wants requests of a fixed size, so we'll slide an
   // AudioBus of that size across the |output_buffer|.
   while (frames_remaining != 0) {
-    int frames_this_iteration =
-        std::min(output_params_.frames_per_buffer(), frames_remaining);
-
-    int offset_into_buffer = output_buffer->frame_count() - frames_remaining;
+    // It's important that this is a multiple of AudioBus::kChannelAlignment in
+    // all requests except for the last, otherwise downstream SIMD optimizations
+    // will crash on unaligned data.
+    const int frames_this_iteration = std::min(
+        static_cast<int>(SincResampler::kDefaultRequestSize), frames_remaining);
+    const int offset_into_buffer =
+        output_buffer->frame_count() - frames_remaining;
 
     // Wrap the portion of the AudioBuffer in an AudioBus so the AudioConverter
     // can fill it.

media/base/audio_buffer_converter_unittest.cc

@@ -12,6 +12,8 @@
 
 namespace media {
 
+// Important: Use an odd buffer size here so SIMD issues are caught.
+const int kOutFrameSize = 441;
 const int kOutSampleRate = 44100;
 const ChannelLayout kOutChannelLayout = CHANNEL_LAYOUT_STEREO;
 const int kOutChannelCount = 2;
@@ -39,7 +41,7 @@ class AudioBufferConverterTest : public ::testing::Test {
                                   kOutChannelLayout,
                                   kOutSampleRate,
                                   16,
-                                  512);
+                                  kOutFrameSize);
     ResetConverter(output_params);
   }