Support (E)AC3 passthrough

media/audio/android/audio_track_output_stream.cc

+// Copyright 2017 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/audio/android/audio_track_output_stream.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/logging.h"
+#include "base/single_thread_task_runner.h"
+#include "base/time/default_tick_clock.h"
+#include "jni/AudioTrackOutputStream_jni.h"
+#include "media/audio/audio_manager_base.h"
+
+using base::android::AttachCurrentThread;
+
+namespace media {
+
+// Android audio format. For more information, please see:
+// https://developer.android.com/reference/android/media/AudioFormat.html
+enum {
+  kEncodingPcmFloat = 4,  // ENCODING_PCM_FLOAT
+  kEncodingAc3 = 5,       // ENCODING_AC3
+  kEncodingEac3 = 6,      // ENCODING_E_AC3
+};
+
+AudioTrackOutputStream::AudioTrackOutputStream(AudioManagerBase* manager,
+                                               const AudioParameters& params)
+    : params_(params),
+      audio_manager_(manager),
+      callback_(nullptr),

[DaleCurtis, 2017/06/15 21:46:31]

Inline initialize these parameters in the header file.

[AndyWu, 2017/08/02 01:43:38]

Done.

+      audio_bus_(AudioBus::Create(params_)),
+      muted_(false),
+      volume_(1.0),
+      total_read_frames_(0),
+      tick_clock_(new base::DefaultTickClock()) {

[DaleCurtis, 2017/06/15 21:46:31]

No need for this unless you're going to add a test for this class?

[AndyWu, 2017/08/02 01:43:38]

Done.

+  audio_bus_->Zero();
+}
+
+AudioTrackOutputStream::~AudioTrackOutputStream() {
+  DCHECK(!callback_);
+}
+
+bool AudioTrackOutputStream::Open() {
+  DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+  JNIEnv* env = AttachCurrentThread();
+  j_audio_output_stream_.Reset(Java_AudioTrackOutputStream_create(env));
+
+  int format = kEncodingPcmFloat;
+  if (params_.IsBitstreamFormat()) {
+    if (params_.format() == AudioParameters::AUDIO_BITSTREAM_AC3) {
+      format = kEncodingAc3;
+    } else if (params_.format() == AudioParameters::AUDIO_BITSTREAM_EAC3) {
+      format = kEncodingEac3;
+    } else {
+      NOTREACHED();
+    }
+  }
+
+  return Java_AudioTrackOutputStream_open(env, j_audio_output_stream_.obj(),
+                                          params_.channels(),
+                                          params_.sample_rate(), format);
+}
+
+void AudioTrackOutputStream::Start(AudioSourceCallback* callback) {
+  DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+  callback_ = callback;
+  total_read_frames_ = 0;
+  Java_AudioTrackOutputStream_start(AttachCurrentThread(),
+                                    j_audio_output_stream_.obj(),
+                                    reinterpret_cast<intptr_t>(this));
+}
+
+void AudioTrackOutputStream::Stop() {
+  DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+  Java_AudioTrackOutputStream_stop(AttachCurrentThread(),
+                                   j_audio_output_stream_.obj());
+  callback_ = nullptr;
+}
+
+void AudioTrackOutputStream::Close() {
+  DCHECK(!callback_);
+  DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+
+  Java_AudioTrackOutputStream_close(AttachCurrentThread(),
+                                    j_audio_output_stream_.obj());
+  audio_manager_->ReleaseOutputStream(this);
+}
+
+void AudioTrackOutputStream::SetMute(bool muted) {
+  if (muted_ == muted)
+    return;
+
+  muted_ = muted;
+  Java_AudioTrackOutputStream_setVolume(AttachCurrentThread(),
+                                        j_audio_output_stream_.obj(),
+                                        muted_ ? 0.0 : volume_);
+}
+
+void AudioTrackOutputStream::SetVolume(double volume) {
+  // Track |volume_| since AudioTrack uses a scaled value.
+  volume_ = volume;
+  if (muted_)
+    return;
+
+  Java_AudioTrackOutputStream_setVolume(AttachCurrentThread(),
+                                        j_audio_output_stream_.obj(), volume);
+};
+
+void AudioTrackOutputStream::GetVolume(double* volume) {
+  *volume = volume_;
+};
+
+// AudioOutputStream::SourceCallback implementation methods called from Java.
+int AudioTrackOutputStream::OnMoreData(JNIEnv* env,
+                                       jobject obj,
+                                       jobject audio_data,
+                                       int total_played_frames) {

[DaleCurtis, 2017/06/15 21:46:31]

As Chris notes, this should be an int64_t.

[AndyWu, 2017/08/02 01:43:38]

AudioTrack.getPlaybackHeadPosition()[1] returns a 32 bits integer. The value
really matters is the difference between total_read_frames_ and
total_played_frames, which is coming from AudioTrack.getPlaybackHeadPosition().
Thus, it's fine to use 32 bits for both total_read_frames_ and
total_played_frames and have them overflow, as long as the difference is smaller
than 0x7FFFFFFF, which should be a very safe assumption.

Anyway, using int64_t is probably a more clear way to eliminate concerns of
overflow.

[1]
https://developer.android.com/reference/android/media/AudioTrack.html#getPlay...

[DaleCurtis, 2017/08/03 01:38:10]

Overflow isn't defined for signed types, so if you expect these to overflow I'd
upcast to uint64_t so that's unlikely.

[AndyWu, 2017/08/03 17:11:17]

Well, I consider 0x7FFFFFFF + 1 = 0x80000000 is overflowing for a signed 32-bit
integer, since the value changes from 2147483647 to -2147483648. What I was
trying to explain is that it's fine to have |total_read_frames_| and
|total_played_frames| overflow here. Some examples:
1) When |total_read_frames_| is 0x7FFFFFFA and |total_played_frames| is
0x7FFFFFEA, |delay_in_frame| = 0x7FFFFFFA - 0x7FFFFFEA = 16.
2) When |total_read_frames_| is 0x8000000A and |total_played_frames| is
0x7FFFFFFA, |delay_in_frame| = 0x8000000A - 0x7FFFFFFA = 16.
3) When |total_read_frames_| is 0xFFFFFFFA and |total_played_frames| is
0xFFFFFFEA, |delay_in_frame| = 0xFFFFFFFA - 0xFFFFFFEA = 16.
4) When |total_read_frames_| is 0x0000000A and |total_played_frames| is
0xFFFFFFFA, |delay_in_frame| = 0x0000000A - 0xFFFFFFFA = 16.

Anyway, I already changed them to 64-bit integer in
https://chromium-review.googlesource.com/c/596720, so they are unlikely to
overflow.

[DaleCurtis, 2017/08/03 17:22:55]

Thanks for changing it. For future reference, what I mean by undefined behavior
(and what it typically refers to) is that the compiler may behave in undefined
ways. To wit, most compilers take advantage of signed overflow being undefined
to make some optimizations:

https://kristerw.blogspot.com/2016/02/how-undefined-signed-overflow-enables.html

Depending on what you're doing the compiler may do something that totally breaks
the assumptions you've stated above.

[AndyWu, 2017/08/03 21:58:45]

Thanks for the great information. :) It does make overflow a danger behavior.

+  if (!callback_)
+    return 0;
+
+  int delay_in_frame = total_read_frames_ - total_played_frames;

[DaleCurtis, 2017/06/15 21:46:31]

Ditto; int64_t.

[AndyWu, 2017/08/02 01:43:38]

Done.

+  if (delay_in_frame < 0)

[DaleCurtis, 2017/06/15 21:46:31]

Should be impossible?, DCHECK instead?

[AndyWu, 2017/08/02 01:43:38]

Normally, it should not happen. However, it could happen when data underflow.

+    delay_in_frame = 0;
+  base::TimeDelta delay = base::TimeDelta::FromSecondsD(

[DaleCurtis, 2017/06/15 21:46:31]

Use AudioTimestampHelper::FramesToTime().

[AndyWu, 2017/08/02 01:43:38]

Done.

+      static_cast<double>(delay_in_frame) / params_.sample_rate());
+
+  callback_->OnMoreData(delay, tick_clock_->NowTicks(), 0, audio_bus_.get());
+
+  if (audio_bus_->data_size() <= 0)
+    return 0;
+
+  total_read_frames_ += audio_bus_->frames();
+
+  void* native_bus = env->GetDirectBufferAddress(audio_data);

[DaleCurtis, 2017/06/15 21:46:31]

Get this pointer ahead of time and use AudioBus::WrapMemory() for the bus passed
into OnMoreData() to avoid the extra copy? Requires that the data block be sized
appropriately...

[AndyWu, 2017/08/02 01:43:38]

TBD

+  memcpy(native_bus, audio_bus_->channel(0), audio_bus_->data_size());
+  return audio_bus_->data_size();
+}
+
+void AudioTrackOutputStream::OnError(JNIEnv* env, jobject obj) {
+  DCHECK(callback_);
+  callback_->OnError();
+}
+
+// static
+bool AudioTrackOutputStream::RegisterAudioTrackOutputStream(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+}  // namespace media