Implement audio recording for Linux via ALSA.

media/audio/linux/alsa_input.cc

+// Copyright (c) 2010 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/linux/alsa_input.h"
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/message_loop.h"
+#include "base/scoped_ptr.h"
+#include "base/time.h"
+#include "media/audio/linux/alsa_util.h"
+#include "media/audio/linux/alsa_wrapper.h"
+
+namespace {
+
+const int kNumPacketsInRingBuffer = 3;
+
+// If a read failed with no audio data, try again after this duration.
+const int kNoAudioReadAgainTimeoutMs = 20;
+
+const char kDefaultDevice1[] = "default";
+const char kDefaultDevice2[] = "plug:default";
+
+}  // namespace
+
+const char* AlsaPcmInputStream::kAutoSelectDevice = "";
+
+AlsaPcmInputStream::AlsaPcmInputStream(const std::string& device_name,
+                                       const AudioParameters& params,
+                                       int samples_per_packet,
+                                       AlsaWrapper* wrapper)
+    : device_name_(device_name),
+      params_(params),
+      samples_per_packet_(samples_per_packet),
+      bytes_per_packet_(samples_per_packet_ *
+                        (params.channels * params.bits_per_sample) / 8),
+      wrapper_(wrapper),
+      packet_duration_ms_(
+          (samples_per_packet_ * base::Time::kMillisecondsPerSecond) /
+          params.sample_rate),
+      callback_(NULL),
+      device_handle_(NULL),
+      ALLOW_THIS_IN_INITIALIZER_LIST(task_factory_(this)) {
+}
+
+bool AlsaPcmInputStream::Open() {
+  if (device_handle_)
+    return false;  // Already open.
+
+  snd_pcm_format_t pcm_format = alsa_util::BitsToFormat(
+      params_.bits_per_sample);
+  if (pcm_format == SND_PCM_FORMAT_UNKNOWN) {
+    LOG(WARNING) << "Unsupported bits per sample: "
+                 << params_.bits_per_sample;
+    return false;
+  }
+
+  int latency_us = packet_duration_ms_ * kNumPacketsInRingBuffer *
+      base::Time::kMicrosecondsPerMillisecond;
+  if (device_name_ == kAutoSelectDevice) {
+    device_handle_ = alsa_util::OpenCaptureDevice(wrapper_, kDefaultDevice1,
+                                                  params_.channels,
+                                                  params_.sample_rate,
+                                                  pcm_format, latency_us);
+    if (!device_handle_) {
+      device_handle_ = alsa_util::OpenCaptureDevice(wrapper_, kDefaultDevice2,
+                                                    params_.channels,
+                                                    params_.sample_rate,
+                                                    pcm_format, latency_us);
+    }
+  } else {
+    device_handle_ = alsa_util::OpenCaptureDevice(wrapper_,
+                                                  device_name_.c_str(),
+                                                  params_.channels,
+                                                  params_.sample_rate,
+                                                  pcm_format, latency_us);
+  }
+
+  if (device_handle_)
+    audio_packet_.reset(new uint8[bytes_per_packet_]);
+
+  return device_handle_ != NULL;
+}
+
+void AlsaPcmInputStream::Start(AudioInputCallback* callback) {
+  DCHECK(!callback_ && callback);
+  callback_ = callback;
+  int error = wrapper_->PcmPrepare(device_handle_);
+  if (error < 0) {
+    HandleError("PcmPrepare", error);
+  } else {
+    error = wrapper_->PcmStart(device_handle_);
+    if (error < 0)
+      HandleError("PcmStart", error);
+  }
+
+  if (error < 0) {
+    callback_ = NULL;
+  } else {
+    // We start reading data a little later than when the packet might have got
+    // filled, to accommodate some delays in the audio driver. This could
+    // also give us a smooth read sequence going forward.
+    int64 delay_ms = packet_duration_ms_ + kNoAudioReadAgainTimeoutMs;
+    next_read_time_ = base::Time::Now() + base::TimeDelta::FromMilliseconds(
+        delay_ms);
+    MessageLoop::current()->PostDelayedTask(
+        FROM_HERE,
+        task_factory_.NewRunnableMethod(&AlsaPcmInputStream::ReadAudio),
+        delay_ms);
+  }
+}
+
+bool AlsaPcmInputStream::Recover(int original_error) {
+  int error = wrapper_->PcmRecover(device_handle_, original_error, 1);
+  if (error < 0) {
+    // Docs say snd_pcm_recover returns the original error if it is not one
+    // of the recoverable ones, so this log message will probably contain the
+    // same error twice.
+    LOG(WARNING) << "Unable to recover from \""
+                 << wrapper_->StrError(original_error) << "\": "
+                 << wrapper_->StrError(error);
+    return false;
+  }
+
+  if (original_error == -EPIPE) {  // Buffer underrun/overrun.
+    // For capture streams we have to repeat the explicit start() to get
+    // data flowing again.
+    error = wrapper_->PcmStart(device_handle_);
+    if (error < 0) {
+      HandleError("PcmStart", error);
+      return false;
+    }
+  }
+
+  return true;
+}
+
+void AlsaPcmInputStream::ReadAudio() {
+  DCHECK(callback_);
+
+  snd_pcm_sframes_t frames = wrapper_->PcmAvailUpdate(device_handle_);
+  if (frames < 0) {  // Potentially recoverable error?
+    LOG(WARNING) << "PcmAvailUpdate(): " << wrapper_->StrError(frames);
+    Recover(frames);
+  }
+
+  if (frames < samples_per_packet_) {
+    // Not enough data yet or error happened. In both cases wait for a very
+    // small duration before checking again.
+    MessageLoop::current()->PostDelayedTask(
+        FROM_HERE,
+        task_factory_.NewRunnableMethod(&AlsaPcmInputStream::ReadAudio),
+        kNoAudioReadAgainTimeoutMs);
+    return;
+  }
+
+  int num_packets = frames / samples_per_packet_;
+  while (num_packets--) {
+    int frames_read = wrapper_->PcmReadi(device_handle_, audio_packet_.get(),
+                                         samples_per_packet_);
+    if (frames_read == samples_per_packet_) {
+      callback_->OnData(this, audio_packet_.get(), bytes_per_packet_);
+    } else {
+      LOG(WARNING) << "PcmReadi returning less than expected frames: "
+                   << frames_read << " vs. " << samples_per_packet_
+                   << ". Dropping this packet.";
+    }
+  }
+
+  next_read_time_ += base::TimeDelta::FromMilliseconds(packet_duration_ms_);
+  int64 delay_ms = (next_read_time_ - base::Time::Now()).InMilliseconds();
+  if (delay_ms < 0) {
+    LOG(WARNING) << "Audio read callback behind schedule by "
+                 << (packet_duration_ms_ - delay_ms) << " (ms).";
+    delay_ms = 0;
+  }
+
+  MessageLoop::current()->PostDelayedTask(
+      FROM_HERE,
+      task_factory_.NewRunnableMethod(&AlsaPcmInputStream::ReadAudio),
+      delay_ms);
+}
+
+void AlsaPcmInputStream::Stop() {
+  if (!device_handle_ || !callback_)
+    return;
+
+  task_factory_.RevokeAll();  // Cancel the next scheduled read.
+  int error = wrapper_->PcmDrop(device_handle_);
+  if (error < 0)
+    HandleError("PcmDrop", error);
+}
+
+void AlsaPcmInputStream::Close() {
+  // Check in case we were already closed or not initialized yet.
+  if (!device_handle_ || !callback_)
+    return;
+
+  task_factory_.RevokeAll();  // Cancel the next scheduled read.
+  int error = alsa_util::CloseDevice(wrapper_, device_handle_);
+  if (error < 0)
+    HandleError("PcmClose", error);
+
+  audio_packet_.reset();
+  device_handle_ = NULL;
+  callback_->OnClose(this);
+}
+
+void AlsaPcmInputStream::HandleError(const char* method, int error) {
+  LOG(WARNING) << method << ": " << wrapper_->StrError(error);
+  callback_->OnError(this, error);
+}
+