Audio software mixer.

media/audio/audio_output_mixer.cc

+// 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/audio/audio_output_mixer.h"
+
+#include <algorithm>
+
+#include "base/bind.h"
+#include "base/compiler_specific.h"
+#include "base/message_loop.h"
+#include "base/time.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_output_proxy.h"
+#include "media/audio/audio_util.h"
+
+namespace media {
+
+AudioOutputMixer::AudioOutputMixer(AudioManager* audio_manager,
+                                   const AudioParameters& params,
+                                   const base::TimeDelta& close_delay)
+    : AudioOutputDispatcher(audio_manager, params),
+      ALLOW_THIS_IN_INITIALIZER_LIST(weak_this_(this)),
+      close_timer_(FROM_HERE,
+                   close_delay,
+                   weak_this_.GetWeakPtr(),
+                   &AudioOutputMixer::ClosePhysicalStream) {
+  // TODO(enal): align data.
+  mixer_data_.reset(new uint8[params_.GetBytesPerBuffer()]);
+}
+
+AudioOutputMixer::~AudioOutputMixer() {
+}
+
+bool AudioOutputMixer::OpenStream() {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+
+  if (physical_stream_.get())
+    return true;
+  AudioOutputStream* stream = audio_manager_->MakeAudioOutputStream(params_);
+  if (!stream)
+    return false;
+  if (!stream->Open()) {
+    stream->Close();
+    return false;
+  }
+  physical_stream_.reset(stream);
+  close_timer_.Reset();
+  return true;
+}
+
+bool AudioOutputMixer::StartStream(
+    AudioOutputStream::AudioSourceCallback* callback,
+    AudioOutputProxy* stream_proxy) {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+
+  // May need to re-open the physical stream if no active proxies and
+  // enough time had pass.
+  OpenStream();
+  if (!physical_stream_.get())
+    return false;
+
+  double volume = 0.0;
+  stream_proxy->GetVolume(&volume);
+  bool should_start = proxies_.empty();
+  {
+    base::AutoLock lock(lock_);
+    ProxyData* proxy_data = &proxies_[stream_proxy];
+    proxy_data->audio_source_callback = callback;
+    proxy_data->volume = volume;
+    proxy_data->pending_bytes = 0;
+  }
+  // We cannot start physical stream under the lock,
+  // OnMoreData() would try acquiring it...
+  if (should_start) {
+    physical_stream_->SetVolume(1.0);
+    physical_stream_->Start(this);
+  }
+  return true;
+}
+
+void AudioOutputMixer::StopStream(AudioOutputProxy* stream_proxy) {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+
+  // Because of possible deadlock we cannot stop physical stream under the lock
+  // (physical_stream_->Stop() can call OnError(), and it acquires the lock to
+  // iterate through proxies), so acquire the lock, update proxy list, release
+  // the lock, and only then stop physical stream if necessary.
+  bool stop_physical_stream = false;
+  {
+    base::AutoLock lock(lock_);
+    ProxyMap::iterator it = proxies_.find(stream_proxy);
+    if (it != proxies_.end()) {
+      proxies_.erase(it);
+      stop_physical_stream = proxies_.empty();
+    }
+  }
+  if (physical_stream_.get()) {
+    if (stop_physical_stream)
+      physical_stream_->Stop();
+    close_timer_.Reset();
+  }
+}
+
+void AudioOutputMixer::StreamVolumeSet(AudioOutputProxy* stream_proxy,
+                                       double volume) {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+
+  ProxyMap::iterator it = proxies_.find(stream_proxy);
+
+  // Do nothing if stream is not currently playing.
+  if (it != proxies_.end()) {
+    base::AutoLock lock(lock_);
+    it->second.volume = volume;
+  }
+}
+
+void AudioOutputMixer::CloseStream(AudioOutputProxy* stream_proxy) {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+
+  StopStream(stream_proxy);
+}
+
+void AudioOutputMixer::Shutdown() {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+
+  // Cancel any pending tasks to close physical stream.
+  weak_this_.InvalidateWeakPtrs();
+
+  while (!proxies_.empty()) {
+    CloseStream(proxies_.begin()->first);
+  }
+  ClosePhysicalStream();
+
+  // No AudioOutputProxy objects should hold a reference to us when we get
+  // to this stage.
+  DCHECK(HasOneRef()) << "Only the AudioManager should hold a reference";
+}
+
+void AudioOutputMixer::ClosePhysicalStream() {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+
+  if (proxies_.empty() && physical_stream_.get() != NULL)
+    physical_stream_.release()->Close();
+}
+
+// AudioSourceCallback implementation.
+uint32 AudioOutputMixer::OnMoreData(AudioOutputStream* stream,
+                                    uint8* dest,
+                                    uint32 max_size,
+                                    AudioBuffersState buffers_state) {
+  max_size = std::min(max_size,
+                      static_cast<uint32>(params_.GetBytesPerBuffer()));
+  // TODO(enal): consider getting rid of lock as it is in time-critical code.
+  //             E.g. swap |proxies_| with local variable, and merge 2 lists
+  //             at the end. That would speed things up but complicate stopping
+  //             the stream.
+  base::AutoLock lock(lock_);
+  if (proxies_.empty())
+    return 0;
+  uint32 actual_total_size = 0;
+  uint32 bytes_per_sample = params_.bits_per_sample() >> 3;
+
+  // Go through all the streams, getting data for every one of them
+  // and mixing it into destination.
+  // Minor optimization: for the first stream we are writing data directly into
+  // destination. This way we don't have to mix the data when there is only one
+  // active stream, and net win in other cases, too.
+  bool first_stream = true;
+  uint8* actual_dest = dest;
+  for (ProxyMap::iterator it = proxies_.begin(); it != proxies_.end(); ++it) {
+    AudioOutputProxy* stream_proxy = it->first;
+    ProxyData* proxy_data = &it->second;
+    // TODO(enal): We don't know |pending _bytes| for individual stream, and we
+    // should give that value to individual stream's OnMoreData(). I believe it
+    // can be used there to evaluate exact position of data it should return.
+    // Current code "sorta works" if everything works perfectly, but would have
+    // problems if some of the buffers are only partially filled -- we don't
+    // know how how much data was in the buffer OS returned to us, so we cannot
+    // correctly calculate new value. If we know number of buffers we can solve
+    // the problem by storing not one value but vector of them.
+    int pending_bytes = std::min(proxy_data->pending_bytes,
+                                 buffers_state.pending_bytes);
+    // Note: there is no way we can deduce hardware_delay_bytes for the
+    // particular proxy stream. Use zero instead.
+    uint32 actual_size = proxy_data->audio_source_callback->OnMoreData(
+        stream_proxy,
+        actual_dest,
+        max_size,
+        AudioBuffersState(pending_bytes, 0));
+
+    // Should update pending_bytes for each proxy.
+    // If stream ended, pending_bytes goes down by max_size.
+    if (actual_size == 0) {
+      pending_bytes -= max_size;
+      proxy_data->pending_bytes = std::max(pending_bytes, 0);
+      continue;
+    }
+
+    // Otherwise, it goes up by amount of data. It cannot exceed max amount of
+    // data we can buffer, but we don't know that value. So we increment
+    // pending_bytes unconditionally but adjust it before actual use (which
+    // would be on a next OnMoreData() call).
+    proxy_data->pending_bytes = pending_bytes + actual_size;
+
+    // No need to mix muted stream.
+    double volume = proxy_data->volume;
+    if (volume == 0.0)
+      continue;
+
+    // Different handling for first and all subsequent streams.
+    if (first_stream) {
+      if (volume != 1.0) {
+        media::AdjustVolume(actual_dest,
+                            actual_size,
+                            params_.channels(),
+                            bytes_per_sample,
+                            volume);
+      }
+      if (actual_size < max_size)
+        memset(dest + actual_size, 0, max_size - actual_size);
+      first_stream = false;
+      actual_dest = mixer_data_.get();
+      actual_total_size = actual_size;
+    } else {
+      media::MixStreams(dest,
+                        actual_dest,
+                        actual_size,
+                        bytes_per_sample,
+                        volume);
+      actual_total_size = std::max(actual_size, actual_total_size);
+    }
+  }
+  return actual_total_size;
+}
+
+void AudioOutputMixer::OnError(AudioOutputStream* stream, int code) {
+  base::AutoLock lock(lock_);
+  for (ProxyMap::iterator it = proxies_.begin(); it != proxies_.end(); ++it) {
+    it->second.audio_source_callback->OnError(it->first, code);
+  }
+}
+
+void AudioOutputMixer::WaitTillDataReady() {
+  base::AutoLock lock(lock_);
+  for (ProxyMap::iterator it = proxies_.begin(); it != proxies_.end(); ++it) {
+    it->second.audio_source_callback->WaitTillDataReady();
+  }
+}
+
+}  // namespace media