Add the option of compressing speech input audio using FLAC.

chrome/browser/speech/audio_encoder.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 "chrome/browser/speech/audio_encoder.h"
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/scoped_ptr.h"
+#include "base/stl_util-inl.h"
+#include "base/string_number_conversions.h"
+#include "third_party/flac/flac.h"
+#include "third_party/speex/speex.h"
+
+using std::string;
+
+namespace {
+
+//-------------------------------- FLACEncoder ---------------------------------
+
+const char* const kContentTypeFLAC = "audio/x-flac; rate=";
+const int kFLACCompressionLevel = 0;  // 0 for speed
+
+class FLACEncoder : public speech_input::AudioEncoder {
+ public:
+  FLACEncoder(int sampling_rate, int bits_per_sample);
+  virtual ~FLACEncoder();
+  virtual void Encode(const short* samples, int num_samples);
+  virtual void Flush();
+
+ private:
+  static FLAC__StreamEncoderWriteStatus WriteCallback(
+      const FLAC__StreamEncoder* encoder,
+      const FLAC__byte buffer[],
+      size_t bytes,
+      unsigned samples,
+      unsigned current_frame,
+      void* client_data);
+
+  FLAC__StreamEncoder* encoder_;
+  bool is_encoder_initialized_;
+
+  DISALLOW_COPY_AND_ASSIGN(FLACEncoder);
+};
+
+FLAC__StreamEncoderWriteStatus FLACEncoder::WriteCallback(
+    const FLAC__StreamEncoder* encoder,
+    const FLAC__byte buffer[],
+    size_t bytes,
+    unsigned samples,
+    unsigned current_frame,
+    void* client_data) {
+  FLACEncoder* me = static_cast<FLACEncoder*>(client_data);
+  DCHECK(me->encoder_ == encoder);
+  me->AppendToBuffer(new string(reinterpret_cast<const char*>(buffer), bytes));
+  return FLAC__STREAM_ENCODER_WRITE_STATUS_OK;
+}
+
+FLACEncoder::FLACEncoder(int sampling_rate, int bits_per_sample)
+    : AudioEncoder(std::string(kContentTypeFLAC) +
+                   base::IntToString(sampling_rate)),
+      encoder_(FLAC__stream_encoder_new()),
+      is_encoder_initialized_(false) {
+  FLAC__stream_encoder_set_channels(encoder_, 1);
+  FLAC__stream_encoder_set_bits_per_sample(encoder_, bits_per_sample);
+  FLAC__stream_encoder_set_sample_rate(encoder_, sampling_rate);
+  FLAC__stream_encoder_set_compression_level(encoder_, kFLACCompressionLevel);
+
+  // Initializing the encoder will cause sync bytes to be written to
+  // its output stream, so we wait until the first call to this method
+  // before doing so.
+}
+
+FLACEncoder::~FLACEncoder() {
+  FLAC__stream_encoder_delete(encoder_);
+}
+
+void FLACEncoder::Encode(const short* samples, int num_samples) {
+  if (!is_encoder_initialized_) {
+    const FLAC__StreamEncoderInitStatus encoder_status =
+        FLAC__stream_encoder_init_stream(encoder_, WriteCallback, NULL, NULL,
+                                         NULL, this);
+    DCHECK(encoder_status == FLAC__STREAM_ENCODER_INIT_STATUS_OK);
+    is_encoder_initialized_ = true;
+  }
+
+  // FLAC encoder wants samples as int32s.
+  scoped_ptr<FLAC__int32> flac_samples(new FLAC__int32[num_samples]);
+  FLAC__int32* flac_samples_ptr = flac_samples.get();
+  for (int i = 0; i < num_samples; ++i)
+    flac_samples_ptr[i] = samples[i];
+
+  FLAC__stream_encoder_process(encoder_, &flac_samples_ptr, num_samples);
+}
+
+void FLACEncoder::Flush() {
+  FLAC__stream_encoder_finish(encoder_);
+}
+
+//-------------------------------- SpeexEncoder --------------------------------
+
+const char* const kContentTypeSpeex = "audio/x-speex-with-header-byte; rate=";
+const int kSpeexEncodingQuality = 8;
+const int kMaxSpeexFrameLength = 110;  // (44kbps rate sampled at 32kHz).
+
+// Since the frame length gets written out as a byte in the encoded packet,
+// make sure it is within the byte range.
+COMPILE_ASSERT(kMaxSpeexFrameLength <= 0xFF, invalidLength);
+
+class SpeexEncoder : public speech_input::AudioEncoder {
+ public:
+  SpeexEncoder(int sampling_rate);
+  virtual void Encode(const short* samples, int num_samples);
+  virtual void Flush() {}
+
+ private:
+  void* encoder_state_;
+  SpeexBits bits_;
+  int samples_per_frame_;
+  char encoded_frame_data_[kMaxSpeexFrameLength + 1];  // +1 for the frame size.
+  DISALLOW_COPY_AND_ASSIGN(SpeexEncoder);
+};
+
+SpeexEncoder::SpeexEncoder(int sampling_rate)
+    : AudioEncoder(std::string(kContentTypeSpeex) +
+                   base::IntToString(sampling_rate)) {
+   // speex_bits_init() does not initialize all of the |bits_| struct.
+   memset(&bits_, 0, sizeof(bits_));
+   speex_bits_init(&bits_);
+   encoder_state_ = speex_encoder_init(&speex_wb_mode);
+   DCHECK(encoder_state_);
+   speex_encoder_ctl(encoder_state_, SPEEX_GET_FRAME_SIZE, &samples_per_frame_);
+   DCHECK(samples_per_frame_ > 0);
+   int quality = kSpeexEncodingQuality;
+   speex_encoder_ctl(encoder_state_, SPEEX_SET_QUALITY, &quality);
+   int vbr = 1;
+   speex_encoder_ctl(encoder_state_, SPEEX_SET_VBR, &vbr);
+   memset(encoded_frame_data_, 0, sizeof(encoded_frame_data_));
+}
+
+void SpeexEncoder::Encode(const short* samples, int num_samples) {
+  // Drop incomplete frames, typically those which come in when recording stops.
+  num_samples -= (num_samples % samples_per_frame_);
+  for (int i = 0; i < num_samples; i += samples_per_frame_) {
+    speex_bits_reset(&bits_);
+    speex_encode_int(encoder_state_, const_cast<spx_int16_t*>(samples + i),
+                     &bits_);
+
+    // Encode the frame and place the size of the frame as the first byte. This
+    // is the packet format for MIME type x-speex-with-header-byte.
+    int frame_length = speex_bits_write(&bits_, encoded_frame_data_ + 1,
+                                        kMaxSpeexFrameLength);
+    encoded_frame_data_[0] = static_cast<char>(frame_length);
+    AppendToBuffer(new string(encoded_frame_data_, frame_length + 1));
+  }
+}
+
+}  // namespace
+
+namespace speech_input {
+
+AudioEncoder* AudioEncoder::Create(Codec codec,
+                                   int sampling_rate,
+                                   int bits_per_sample) {
+  if (codec == CODEC_FLAC)
+    return new FLACEncoder(sampling_rate, bits_per_sample);
+  return new SpeexEncoder(sampling_rate);
+}
+
+AudioEncoder::AudioEncoder(const std::string& mime_type)
+    : mime_type_(mime_type) {
+}
+
+AudioEncoder::~AudioEncoder() {
+  STLDeleteElements(&audio_buffers_);
+}
+
+bool AudioEncoder::GetEncodedData(std::string* encoded_data) {
+  if (!audio_buffers_.size())
+    return false;
+
+  int audio_buffer_length = 0;
+  for (AudioBufferQueue::iterator it = audio_buffers_.begin();
+       it != audio_buffers_.end(); ++it) {
+    audio_buffer_length += (*it)->length();
+  }
+  encoded_data->reserve(audio_buffer_length);
+  for (AudioBufferQueue::iterator it = audio_buffers_.begin();
+       it != audio_buffers_.end(); ++it) {
+    encoded_data->append(*(*it));
+  }
+
+  return true;
+}
+
+void AudioEncoder::AppendToBuffer(std::string* item) {
+  audio_buffers_.push_back(item);
+}
+
+}  // namespace speech_input