WebCodecs: Copy decoded output to AudioBuffer

AudioFrame will now contain real audio output!

Bug: 1094084
Change-Id: I4f0c2388f843afbfedc8713352492cb469061ea5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2339671
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798450}

third_party/blink/renderer/modules/webcodecs/audio_frame.cc

@@ -3,7 +3,10 @@
 // found in the LICENSE file.
 
 #include "third_party/blink/renderer/modules/webcodecs/audio_frame.h"
+#include "media/base/audio_buffer.h"
+#include "media/base/audio_bus.h"
 #include "third_party/blink/renderer/bindings/modules/v8/v8_audio_frame_init.h"
+#include "third_party/blink/renderer/modules/webaudio/audio_buffer.h"
 
 namespace blink {
 
@@ -19,7 +22,26 @@ AudioFrame::AudioFrame(AudioFrameInit* init)
 
 AudioFrame::AudioFrame(scoped_refptr<media::AudioBuffer> buffer)
     : timestamp_(buffer->timestamp().InMicroseconds()) {
-  // FIXME - use the |buffer| to initialize AudioBuffer.
+  buffer_ = AudioBuffer::CreateUninitialized(
+      buffer->channel_count(), buffer->frame_count(), buffer->sample_rate());
+
+  // Wrap blink buffer a media::AudioBus so we can interface with
+  // media::AudioBuffer to copy the data out.
+  auto media_bus_wrapper =
+      media::AudioBus::CreateWrapper(buffer->channel_count());
+  for (int i = 0; i < media_bus_wrapper->channels(); ++i) {
+    DCHECK_EQ(buffer_->getChannelData(i)->byteLengthAsSizeT(),
+              buffer->frame_count() * sizeof(float));
+    float* channel_data = buffer_->getChannelData(i)->Data();
+    media_bus_wrapper->SetChannelData(i, channel_data);
+  }
+  media_bus_wrapper->set_frames(buffer->frame_count());
+
+  // Copy the frames.
+  // TODO(chcunningham): Avoid this copy by refactoring blink::AudioBuffer to
+  // ref a media::AudioBuffer and only copy for calls to copyToChannel().
+  buffer->ReadFrames(media_bus_wrapper->frames(), 0 /* source_frame_offset */,
+                     0 /* dest_frame_offset */, media_bus_wrapper.get());
 }
 
 void AudioFrame::close() {