Add a unified audio I/O backend for ChromeOS.

media/audio/cras/cras_unified.cc

Index: media/audio/cras/cras_unified.cc
diff --git a/media/audio/cras/cras_unified.cc b/media/audio/cras/cras_unified.cc
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+++ b/media/audio/cras/cras_unified.cc
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+// Copyright (c) 2012 The Chromium Authors. All rights reserved.

[no longer working on chromium, 2013/03/21 15:38:27]

ditto

[dgreid, 2013/03/21 17:18:44]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/audio/cras/cras_unified.h"
+
+#include <cras_client.h>
+
+#include "base/command_line.h"
+#include "base/logging.h"
+#include "media/audio/audio_util.h"
+#include "media/audio/cras/audio_manager_cras.h"
+#include "media/audio/linux/alsa_util.h"
+
+namespace media {
+
+// Overview of operation:
+// 1) An object of CrasUnifiedStream is created by the AudioManager
+// factory: audio_man->MakeAudioStream().
+// 2) Next some thread will call Open(), at that point a client is created and
+// configured for the correct format and sample rate.
+// 3) Then Start(source) is called and a stream is added to the CRAS client
+// which will create its own thread that periodically calls the source for more
+// data as buffers are being consumed.
+// 4) When finished Stop() is called, which is handled by stopping the stream.
+// 5) Finally Close() is called. It cleans up and notifies the audio manager,
+// which likely will destroy this object.
+//
+// For output-only streams, a unified stream is created with 0 input channels.
+//
+// Simplified data flow for unified streams:
+//
+//   +-------------+                  +------------------+
+//   | CRAS Server |                  | Chrome Client    |
+//   +------+------+    Add Stream    +---------+--------+
+//          |<----------------------------------|
+//          |                                   |
+//          |  buffer_frames captured to shm    |
+//          |---------------------------------->|
+//          |                                   |  UnifiedCallback()
+//          |                                   |  ReadWriteAudio()
+//          |                                   |
+//          |  buffer_frames written to shm     |
+//          |<----------------------------------|
+//          |                                   |
+//         ...  Repeats for each block.        ...
+//          |                                   |
+//          |                                   |
+//          |  Remove stream                    |
+//          |<----------------------------------|
+//          |                                   |
+//
+// Simplified data flow for output only streams:
+//
+//   +-------------+                  +------------------+
+//   | CRAS Server |                  | Chrome Client    |
+//   +------+------+    Add Stream    +---------+--------+
+//          |<----------------------------------|
+//          |                                   |
+//          | Near out of samples, request more |
+//          |---------------------------------->|
+//          |                                   |  UnifiedCallback()
+//          |                                   |  WriteAudio()
+//          |                                   |
+//          |  buffer_frames written to shm     |
+//          |<----------------------------------|
+//          |                                   |
+//         ...  Repeats for each block.        ...
+//          |                                   |
+//          |                                   |
+//          |  Remove stream                    |
+//          |<----------------------------------|
+//          |                                   |
+//
+// For Unified streams the Chrome client is notified whenever buffer_frames have
+// been captured.  For Output streams the client is notified a few milliseconds
+// before the hardware buffer underruns and fills the buffer with another block
+// of audio.
+
+CrasUnifiedStream::CrasUnifiedStream(const AudioParameters& params,
+                                     AudioManagerCras* manager)
+    : client_(NULL),
+      stream_id_(0),
+      samples_per_packet_(params.frames_per_buffer()),
+      bytes_per_frame_(0),
+      frame_rate_(params.sample_rate()),
+      output_channels_(params.channels()),
+      pcm_format_(alsa_util::BitsToFormat(params.bits_per_sample())),
+      is_playing_(false),
+      volume_(1.0),
+      manager_(manager),
+      source_callback_(NULL),
+      input_bus_(NULL),
+      output_bus_(NULL) {
+  unsigned int input_channels = params.input_channels();

[no longer working on chromium, 2013/03/21 15:38:27]

Curiously, why do we need output_channels to be a member but not input_channels?

[dgreid, 2013/03/21 17:18:44]

If there are input channels they will always be the same as output channels
since the input and output format must match.

[dgreid, 2013/03/21 17:18:44]

If there are input channels there will be the same count as the output channels
since the input and output format match.

+
+  // We must have a manager.

[no longer working on chromium, 2013/03/21 15:38:27]

nit, the comment tells nothing, please remove

[dgreid, 2013/03/21 17:18:44]

Done.

+  DCHECK(manager_);

[no longer working on chromium, 2013/03/21 15:38:27]

move the DCHECK to the top of the function.

[dgreid, 2013/03/21 17:18:44]

Done.

+  // Must have at least one input or output.  If there are both they must be the
+  // same.
+  DCHECK(output_channels_  > 0 || input_channels > 0);
+  if (output_channels_ > 0 && input_channels > 0)
+    DCHECK(output_channels_ == input_channels);
+
+  if (input_channels)
+    input_bus_ = AudioBus::Create(input_channels,
+                                  params.frames_per_buffer());
+  if (output_channels_)
+    output_bus_ = AudioBus::Create(params);
+
+  if (output_channels_ && input_channels)
+    stream_direction_ = CRAS_STREAM_UNIFIED;
+  else if (output_channels_)
+    stream_direction_ = CRAS_STREAM_OUTPUT;
+  else
+    NOTREACHED() << "Input only streams not supported by CrasUnifiedStream.";

[no longer working on chromium, 2013/03/21 15:38:27]

move this section up to line 101, and combine with those DCHECKs.

[dgreid, 2013/03/21 17:18:44]

I got rid of it and simlified the checks above, there isn't a way to use unified
for just input yet.

+}
+
+CrasUnifiedStream::~CrasUnifiedStream() {
+  DCHECK(!is_playing_);
+}
+
+bool CrasUnifiedStream::Open() {
+  // Sanity check input values.
+  if (frame_rate_ <= 0) {
+    LOG(WARNING) << "Unsupported audio frequency.";
+    return false;
+  }
+
+  if (pcm_format_ == SND_PCM_FORMAT_UNKNOWN) {
+    LOG(WARNING) << "Unsupported pcm format";
+    return false;
+  }
+
+  // Create the client and connect to the CRAS server.
+  int err = cras_client_create(&client_);

[no longer working on chromium, 2013/03/21 15:38:27]

why do you need variable err?
You can simply do 
if (cras_client_create(&client_) < 0)
...

[dgreid, 2013/03/21 17:18:44]

Done.

+  if (err < 0) {
+    LOG(WARNING) << "Couldn't create CRAS client.\n";
+    client_ = NULL;
+    return false;
+  }
+
+  err = cras_client_connect(client_);
+  if (err) {
+    LOG(WARNING) << "Couldn't connect CRAS client.\n";
+    cras_client_destroy(client_);
+    client_ = NULL;
+    return false;
+  }
+
+  // Then start running the client.
+  err = cras_client_run_thread(client_);
+  if (err) {
+    LOG(WARNING) << "Couldn't run CRAS client.\n";
+    cras_client_destroy(client_);
+    client_ = NULL;
+    return false;
+  }
+
+  return true;
+}
+
+void CrasUnifiedStream::Close() {
+  if (client_) {
+    cras_client_stop(client_);
+    cras_client_destroy(client_);
+    client_ = NULL;
+  }
+
+  // Signal to the manager that we're closed and can be removed.
+  // Should be last call in the method as it deletes "this".
+  manager_->ReleaseOutputStream(this);
+}
+
+void CrasUnifiedStream::Start(AudioSourceCallback* callback) {
+  CHECK(callback);
+  source_callback_ = callback;
+
+  // Only start if we can enter the playing state.
+  if (is_playing_)
+    return;
+
+  // Prepare |audio_format| and |stream_params| for the stream we
+  // will create.
+  cras_audio_format* audio_format = cras_audio_format_create(
+      pcm_format_,
+      frame_rate_,
+      output_channels_);
+  if (audio_format == NULL) {
+    LOG(WARNING) << "Error setting up audio parameters.";
+    callback->OnError(this, -ENOMEM);
+    return;
+  }
+
+  cras_stream_params* stream_params = cras_client_unified_params_create(
+      stream_direction_,
+      samples_per_packet_,
+      CRAS_STREAM_TYPE_DEFAULT,
+      0,
+      this,
+      CrasUnifiedStream::UnifiedCallback,
+      CrasUnifiedStream::StreamError,
+      audio_format);
+  if (stream_params == NULL) {
+    LOG(WARNING) << "Error setting up stream parameters.";
+    callback->OnError(this, -ENOMEM);
+    cras_audio_format_destroy(audio_format);
+    return;
+  }
+
+  // Before starting the stream, save the number of bytes in a frame for use in
+  // the callback.
+  bytes_per_frame_ = cras_client_format_bytes_per_frame(audio_format);
+
+  // Adding the stream will start the audio callbacks requesting data.
+  int err = cras_client_add_stream(client_, &stream_id_, stream_params);
+  if (err < 0) {
+    LOG(WARNING) << "Failed to add the stream";
+    callback->OnError(this, err);
+    cras_audio_format_destroy(audio_format);
+    cras_client_stream_params_destroy(stream_params);
+    return;
+  }
+
+  // Set initial volume.
+  cras_client_set_stream_volume(client_, stream_id_, volume_);
+
+  // Done with config params.
+  cras_audio_format_destroy(audio_format);
+  cras_client_stream_params_destroy(stream_params);
+
+  is_playing_ = true;
+}
+
+void CrasUnifiedStream::Stop() {
+  if (!client_)
+    return;
+
+  // Removing the stream from the client stops audio.
+  cras_client_rm_stream(client_, stream_id_);
+
+  is_playing_ = false;
+}
+
+void CrasUnifiedStream::SetVolume(double volume) {
+  if (!client_)
+    return;
+  volume_ = static_cast<float>(volume);
+  cras_client_set_stream_volume(client_, stream_id_, volume_);
+}
+
+void CrasUnifiedStream::GetVolume(double* volume) {
+  *volume = volume_;
+}
+
+unsigned int CrasUnifiedStream::GetBytesLatency(
+    const struct timespec& latency_ts) {
+  uint32 latency_usec;
+
+  // Treat negative latency (if we are too slow to render) as 0.
+  if (latency_ts.tv_sec < 0 || latency_ts.tv_nsec < 0)

[no longer working on chromium, 2013/03/21 15:38:27]

nit, add {} since else case has more than 1 line.

[dgreid, 2013/03/21 17:18:44]

Done.

+    latency_usec = 0;
+  else
+    latency_usec = (latency_ts.tv_sec * base::Time::kMicrosecondsPerSecond) +
+        latency_ts.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
+
+  double frames_latency =
+      latency_usec * frame_rate_ / base::Time::kMicrosecondsPerSecond;
+
+  return static_cast<unsigned int>(frames_latency * bytes_per_frame_);
+}
+
+// Static callback asking for samples.
+int CrasUnifiedStream::UnifiedCallback(cras_client* client,
+                                       cras_stream_id_t stream_id,
+                                       uint8* input_samples,
+                                       uint8* output_samples,
+                                       unsigned int frames,
+                                       const timespec* input_ts,
+                                       const timespec* output_ts,
+                                       void* arg) {
+  CrasUnifiedStream* me = static_cast<CrasUnifiedStream*>(arg);
+  return me->DispatchCalback(frames,
+                             input_samples,
+                             output_samples,
+                             input_ts,
+                             output_ts);
+}
+
+// Static callback for stream errors.
+int CrasUnifiedStream::StreamError(cras_client* client,
+                                   cras_stream_id_t stream_id,
+                                   int err,
+                                   void* arg) {
+  CrasUnifiedStream* me = static_cast<CrasUnifiedStream*>(arg);
+  me->NotifyStreamError(err);
+  return 0;
+}
+
+// Calls the appropriate rendering function for this type of stream.
+uint32 CrasUnifiedStream::DispatchCalback(size_t frames,
+                                          uint8* input_samples,
+                                          uint8* output_samples,
+                                          const timespec* input_ts,
+                                          const timespec* output_ts) {
+  switch (stream_direction_) {
+    case CRAS_STREAM_OUTPUT:
+      return WriteAudio(frames, output_samples, output_ts);
+    case CRAS_STREAM_INPUT:
+      NOTREACHED() << "CrasUnifiedStream doesn't support input streams.";
+      return 0;
+    case CRAS_STREAM_UNIFIED:
+      return ReadWriteAudio(frames, input_samples, output_samples,
+                            input_ts, output_ts);
+  }
+
+  return 0;
+}
+
+// Note these are run from a real time thread, so don't waste cycles here.
+uint32 CrasUnifiedStream::ReadWriteAudio(size_t frames,
+                                         uint8* input_samples,
+                                         uint8* output_samples,
+                                         const timespec* input_ts,
+                                         const timespec* output_ts) {
+  unsigned int bytes_per_sample = bytes_per_frame_ / output_channels_;
+
+  DCHECK_EQ(frames, static_cast<size_t>(output_bus_->frames()));
+  DCHECK(source_callback_);
+
+  input_bus_->FromInterleaved(input_samples, frames, bytes_per_sample);
+
+  // Determine latency and pass that on to the source.  We have the capture time
+  // of the first input sample and the playback time of the next audio sample
+  // passed from the audio server, add them together for total latency.
+  unsigned int total_delay_bytes;
+  timespec latency_ts  = {0, 0};
+  cras_client_calc_capture_latency(input_ts, &latency_ts);
+  total_delay_bytes = GetBytesLatency(latency_ts);
+  cras_client_calc_playback_latency(output_ts, &latency_ts);
+  total_delay_bytes += GetBytesLatency(latency_ts);
+
+  int frames_filled = source_callback_->OnMoreIOData(
+      input_bus_.get(),
+      output_bus_.get(),
+      AudioBuffersState(0, total_delay_bytes));
+
+  output_bus_->ToInterleaved(frames_filled, bytes_per_sample, output_samples);
+
+  return frames_filled;
+}
+
+uint32 CrasUnifiedStream::WriteAudio(size_t frames,
+                                     uint8* buffer,
+                                     const timespec* sample_ts) {
+  timespec latency_ts  = {0, 0};

[no longer working on chromium, 2013/03/21 15:38:27]

nit, move the declaration to the place where it is being used.

[dgreid, 2013/03/21 17:18:44]

Done.

[dgreid, 2013/03/21 17:18:44]

Done.

+
+  DCHECK_EQ(frames, static_cast<size_t>(output_bus_->frames()));
+
+  // Determine latency and pass that on to the source.
+  cras_client_calc_playback_latency(sample_ts, &latency_ts);
+
+  int frames_filled = source_callback_->OnMoreData(
+      output_bus_.get(), AudioBuffersState(0, GetBytesLatency(latency_ts)));
+
+  // Note: If this ever changes to output raw float the data must be clipped and
+  // sanitized since it may come from an untrusted source such as NaCl.
+  output_bus_->ToInterleaved(
+      frames_filled, bytes_per_frame_ / output_channels_, buffer);
+
+  return frames_filled;
+}
+
+void CrasUnifiedStream::NotifyStreamError(int err) {
+  // This will remove the stream from the client.
+  if (source_callback_)
+    source_callback_->OnError(this, err);
+}
+
+}  // namespace media