Reland: H264 HW encode using VideoToolbox

content/common/gpu/media/vt_video_encode_accelerator_mac.cc

Index: content/common/gpu/media/vt_video_encode_accelerator_mac.cc
diff --git a/media/cast/sender/h264_vt_encoder.cc b/content/common/gpu/media/vt_video_encode_accelerator_mac.cc
similarity index 11%
copy from media/cast/sender/h264_vt_encoder.cc
copy to content/common/gpu/media/vt_video_encode_accelerator_mac.cc
index 33e7366d80a3e534653e8b7cfd94c530fac3f28d..71c80ef3a9f1bfb58b4dc8b5f97769409af42fcb 100644
--- a/media/cast/sender/h264_vt_encoder.cc
+++ b/content/common/gpu/media/vt_video_encode_accelerator_mac.cc
@@ -1,769 +1,552 @@
-// Copyright 2014 The Chromium Authors. All rights reserved.
+// Copyright 2016 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/cast/sender/h264_vt_encoder.h"
+#include "content/common/gpu/media/vt_video_encode_accelerator_mac.h"
 
-#include <stddef.h>
-
-#include <string>
-#include <vector>
-
-#include "base/big_endian.h"
-#include "base/bind.h"
-#include "base/bind_helpers.h"
-#include "base/location.h"
-#include "base/logging.h"
-#include "base/macros.h"
-#include "base/power_monitor/power_monitor.h"
-#include "base/synchronization/lock.h"
-#include "build/build_config.h"
+#include "base/thread_task_runner_handle.h"
+#include "media/base/mac/coremedia_glue.h"
 #include "media/base/mac/corevideo_glue.h"
 #include "media/base/mac/video_frame_mac.h"
-#include "media/cast/common/rtp_time.h"
-#include "media/cast/constants.h"
-#include "media/cast/sender/video_frame_factory.h"
 
-namespace media {
-namespace cast {
+namespace content {
 
 namespace {
 
-// Container for the associated data of a video frame being processed.
-struct InProgressFrameEncode {
-  const RtpTimeTicks rtp_timestamp;
+// TODO(emircan): Check if we can find the actual system capabilities via
+// creating VTCompressionSessions with varying requirements.
+// See crbug.com/584784.
+const size_t kBitsPerByte = 8;
+const size_t kDefaultResolutionWidth = 640;
+const size_t kDefaultResolutionHeight = 480;
+const size_t kMaxFrameRateNumerator = 30;
+const size_t kMaxFrameRateDenominator = 1;
+const size_t kMaxResolutionWidth = 4096;
+const size_t kMaxResolutionHeight = 2160;
+const size_t kNumInputBuffers = 3;
+
+}  // namespace
+
+struct VTVideoEncodeAccelerator::InProgressFrameEncode {
+  InProgressFrameEncode(base::TimeDelta rtp_timestamp,
+                        base::TimeTicks ref_time)
+      : timestamp(rtp_timestamp), reference_time(ref_time) {}
+  const base::TimeDelta timestamp;
   const base::TimeTicks reference_time;
-  const VideoEncoder::FrameEncodedCallback frame_encoded_callback;
-
-  InProgressFrameEncode(RtpTimeTicks rtp,
-                        base::TimeTicks r_time,
-                        VideoEncoder::FrameEncodedCallback callback)
-      : rtp_timestamp(rtp),
-        reference_time(r_time),
-        frame_encoded_callback(callback) {}
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(InProgressFrameEncode);
 };
 
-base::ScopedCFTypeRef<CFDictionaryRef>
-DictionaryWithKeysAndValues(CFTypeRef* keys, CFTypeRef* values, size_t size) {
-  return base::ScopedCFTypeRef<CFDictionaryRef>(CFDictionaryCreate(
-      kCFAllocatorDefault, keys, values, size, &kCFTypeDictionaryKeyCallBacks,
-      &kCFTypeDictionaryValueCallBacks));
-}
+struct VTVideoEncodeAccelerator::EncodeOutput {
+  EncodeOutput(VTEncodeInfoFlags info_flags, CMSampleBufferRef sbuf)
+      : info(info_flags), sample_buffer(sbuf, base::scoped_policy::RETAIN) {}
+  const VTEncodeInfoFlags info;
+  const base::ScopedCFTypeRef<CMSampleBufferRef> sample_buffer;
 
-base::ScopedCFTypeRef<CFDictionaryRef> DictionaryWithKeyValue(CFTypeRef key,
-                                                              CFTypeRef value) {
-  CFTypeRef keys[1] = {key};
-  CFTypeRef values[1] = {value};
-  return DictionaryWithKeysAndValues(keys, values, 1);
-}
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(EncodeOutput);
+};
 
-base::ScopedCFTypeRef<CFArrayRef> ArrayWithIntegers(const int* v, size_t size) {
-  std::vector<CFNumberRef> numbers;
-  numbers.reserve(size);
-  for (const int* end = v + size; v < end; ++v)
-    numbers.push_back(CFNumberCreate(nullptr, kCFNumberSInt32Type, v));
-  base::ScopedCFTypeRef<CFArrayRef> array(CFArrayCreate(
-      kCFAllocatorDefault, reinterpret_cast<const void**>(&numbers[0]),
-      numbers.size(), &kCFTypeArrayCallBacks));
-  for (auto& number : numbers) {
-    CFRelease(number);
-  }
-  return array;
-}
+struct VTVideoEncodeAccelerator::BitstreamBufferRef {
+  BitstreamBufferRef(int32_t id,
+                     scoped_ptr<base::SharedMemory> shm,
+                     size_t size)
+      : id(id), shm(std::move(shm)), size(size) {}
+  const int32_t id;
+  const scoped_ptr<base::SharedMemory> shm;
+  const size_t size;
 
-template <typename NalSizeType>
-void CopyNalsToAnnexB(char* avcc_buffer,
-                      const size_t avcc_size,
-                      std::string* annexb_buffer) {
-  static_assert(sizeof(NalSizeType) == 1 || sizeof(NalSizeType) == 2 ||
-                    sizeof(NalSizeType) == 4,
-                "NAL size type has unsupported size");
-  static const char startcode_3[3] = {0, 0, 1};
-  DCHECK(avcc_buffer);
-  DCHECK(annexb_buffer);
-  size_t bytes_left = avcc_size;
-  while (bytes_left > 0) {
-    DCHECK_GT(bytes_left, sizeof(NalSizeType));
-    NalSizeType nal_size;
-    base::ReadBigEndian(avcc_buffer, &nal_size);
-    bytes_left -= sizeof(NalSizeType);
-    avcc_buffer += sizeof(NalSizeType);
-
-    DCHECK_GE(bytes_left, nal_size);
-    annexb_buffer->append(startcode_3, sizeof(startcode_3));
-    annexb_buffer->append(avcc_buffer, nal_size);
-    bytes_left -= nal_size;
-    avcc_buffer += nal_size;
-  }
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(BitstreamBufferRef);
+};
+
+VTVideoEncodeAccelerator::VTVideoEncodeAccelerator()
+    : client_task_runner_(base::ThreadTaskRunnerHandle::Get()),
+      encoder_thread_("VTEncoderThread"),
+      encoder_task_weak_factory_(this) {
+  encoder_weak_ptr_ = encoder_task_weak_factory_.GetWeakPtr();
 }
 
-// Copy a H.264 frame stored in a CM sample buffer to an Annex B buffer. Copies
-// parameter sets for keyframes before the frame data as well.
-void CopySampleBufferToAnnexBBuffer(CoreMediaGlue::CMSampleBufferRef sbuf,
-                                    std::string* annexb_buffer,
-                                    bool keyframe) {
-  // Perform two pass, one to figure out the total output size, and another to
-  // copy the data after having performed a single output allocation. Note that
-  // we'll allocate a bit more because we'll count 4 bytes instead of 3 for
-  // video NALs.
-
-  OSStatus status;
-
-  // Get the sample buffer's block buffer and format description.
-  auto bb = CoreMediaGlue::CMSampleBufferGetDataBuffer(sbuf);
-  DCHECK(bb);
-  auto fdesc = CoreMediaGlue::CMSampleBufferGetFormatDescription(sbuf);
-  DCHECK(fdesc);
-
-  size_t bb_size = CoreMediaGlue::CMBlockBufferGetDataLength(bb);
-  size_t total_bytes = bb_size;
-
-  size_t pset_count;
-  int nal_size_field_bytes;
-  status = CoreMediaGlue::CMVideoFormatDescriptionGetH264ParameterSetAtIndex(
-      fdesc, 0, nullptr, nullptr, &pset_count, &nal_size_field_bytes);
-  if (status ==
-      CoreMediaGlue::kCMFormatDescriptionBridgeError_InvalidParameter) {
-    DLOG(WARNING) << " assuming 2 parameter sets and 4 bytes NAL length header";
-    pset_count = 2;
-    nal_size_field_bytes = 4;
-  } else if (status != noErr) {
-    DLOG(ERROR)
-        << " CMVideoFormatDescriptionGetH264ParameterSetAtIndex failed: "
-        << status;
-    return;
-  }
+VTVideoEncodeAccelerator::~VTVideoEncodeAccelerator() {
+  DVLOG(3) << __FUNCTION__;
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  if (keyframe) {
-    const uint8_t* pset;
-    size_t pset_size;
-    for (size_t pset_i = 0; pset_i < pset_count; ++pset_i) {
-      status =
-          CoreMediaGlue::CMVideoFormatDescriptionGetH264ParameterSetAtIndex(
-              fdesc, pset_i, &pset, &pset_size, nullptr, nullptr);
-      if (status != noErr) {
-        DLOG(ERROR)
-            << " CMVideoFormatDescriptionGetH264ParameterSetAtIndex failed: "
-            << status;
-        return;
-      }
-      total_bytes += pset_size + nal_size_field_bytes;
-    }
-  }
+  Destroy();
+  DCHECK(!encoder_thread_.IsRunning());
+  DCHECK(!encoder_task_weak_factory_.HasWeakPtrs());
+}
 
-  annexb_buffer->reserve(total_bytes);
-
-  // Copy all parameter sets before keyframes.
-  if (keyframe) {
-    const uint8_t* pset;
-    size_t pset_size;
-    for (size_t pset_i = 0; pset_i < pset_count; ++pset_i) {
-      status =
-          CoreMediaGlue::CMVideoFormatDescriptionGetH264ParameterSetAtIndex(
-              fdesc, pset_i, &pset, &pset_size, nullptr, nullptr);
-      if (status != noErr) {
-        DLOG(ERROR)
-            << " CMVideoFormatDescriptionGetH264ParameterSetAtIndex failed: "
-            << status;
-        return;
-      }
-      static const char startcode_4[4] = {0, 0, 0, 1};
-      annexb_buffer->append(startcode_4, sizeof(startcode_4));
-      annexb_buffer->append(reinterpret_cast<const char*>(pset), pset_size);
-    }
-  }
+media::VideoEncodeAccelerator::SupportedProfiles
+VTVideoEncodeAccelerator::GetSupportedProfiles() {
+  DVLOG(3) << __FUNCTION__;
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  // Block buffers can be composed of non-contiguous chunks. For the sake of
-  // keeping this code simple, flatten non-contiguous block buffers.
-  base::ScopedCFTypeRef<CoreMediaGlue::CMBlockBufferRef> contiguous_bb(
-      bb, base::scoped_policy::RETAIN);
-  if (!CoreMediaGlue::CMBlockBufferIsRangeContiguous(bb, 0, 0)) {
-    contiguous_bb.reset();
-    status = CoreMediaGlue::CMBlockBufferCreateContiguous(
-        kCFAllocatorDefault, bb, kCFAllocatorDefault, nullptr, 0, 0, 0,
-        contiguous_bb.InitializeInto());
-    if (status != noErr) {
-      DLOG(ERROR) << " CMBlockBufferCreateContiguous failed: " << status;
-      return;
-    }
+  SupportedProfiles profiles;
+  // Check if HW encoder is supported initially.
+  videotoolbox_glue_ = VideoToolboxGlue::Get();
+  if (!videotoolbox_glue_) {
+    DLOG(ERROR) << "Failed creating VideoToolbox glue.";
+    return profiles;
   }
-
-  // Copy all the NAL units. In the process convert them from AVCC format
-  // (length header) to AnnexB format (start code).
-  char* bb_data;
-  status = CoreMediaGlue::CMBlockBufferGetDataPointer(contiguous_bb, 0, nullptr,
-                                                      nullptr, &bb_data);
-  if (status != noErr) {
-    DLOG(ERROR) << " CMBlockBufferGetDataPointer failed: " << status;
-    return;
+  const bool rv = CreateCompressionSession(
+      media::video_toolbox::DictionaryWithKeysAndValues(nullptr, nullptr, 0),
+      gfx::Size(kDefaultResolutionWidth, kDefaultResolutionHeight), true);
+  DestroyCompressionSession();
+  if (!rv) {
+    VLOG(1)
+        << "Hardware encode acceleration is not available on this platform.";
+    return profiles;
   }
 
-  if (nal_size_field_bytes == 1) {
-    CopyNalsToAnnexB<uint8_t>(bb_data, bb_size, annexb_buffer);
-  } else if (nal_size_field_bytes == 2) {
-    CopyNalsToAnnexB<uint16_t>(bb_data, bb_size, annexb_buffer);
-  } else if (nal_size_field_bytes == 4) {
-    CopyNalsToAnnexB<uint32_t>(bb_data, bb_size, annexb_buffer);
-  } else {
-    NOTREACHED();
-  }
+  SupportedProfile profile;
+  profile.profile = media::H264PROFILE_BASELINE;
+  profile.max_framerate_numerator = kMaxFrameRateNumerator;
+  profile.max_framerate_denominator = kMaxFrameRateDenominator;
+  profile.max_resolution = gfx::Size(kMaxResolutionWidth, kMaxResolutionHeight);
+  profiles.push_back(profile);
+  return profiles;
 }
 
-}  // namespace
+bool VTVideoEncodeAccelerator::Initialize(
+    media::VideoPixelFormat format,
+    const gfx::Size& input_visible_size,
+    media::VideoCodecProfile output_profile,
+    uint32_t initial_bitrate,
+    Client* client) {
+  DVLOG(3) << __FUNCTION__
+           << ": input_format=" << media::VideoPixelFormatToString(format)
+           << ", input_visible_size=" << input_visible_size.ToString()
+           << ", output_profile=" << output_profile
+           << ", initial_bitrate=" << initial_bitrate;
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(client);
 
-class H264VideoToolboxEncoder::VideoFrameFactoryImpl
-    : public base::RefCountedThreadSafe<VideoFrameFactoryImpl>,
-      public VideoFrameFactory {
- public:
-  // Type that proxies the VideoFrameFactory interface to this class.
-  class Proxy;
-
-  VideoFrameFactoryImpl(const base::WeakPtr<H264VideoToolboxEncoder>& encoder,
-                        const scoped_refptr<CastEnvironment>& cast_environment)
-      : encoder_(encoder), cast_environment_(cast_environment) {}
-
-  scoped_refptr<VideoFrame> MaybeCreateFrame(
-      const gfx::Size& frame_size,
-      base::TimeDelta timestamp) final {
-    if (frame_size.IsEmpty()) {
-      DVLOG(1) << "Rejecting empty video frame.";
-      return nullptr;
-    }
-
-    base::AutoLock auto_lock(lock_);
-
-    // If the pool size does not match, speculatively reset the encoder to use
-    // the new size and return null. Cache the new frame size right away and
-    // toss away the pixel buffer pool to avoid spurious tasks until the encoder
-    // is done resetting.
-    if (frame_size != pool_frame_size_) {
-      DVLOG(1) << "MaybeCreateFrame: Detected frame size change.";
-      cast_environment_->PostTask(
-          CastEnvironment::MAIN, FROM_HERE,
-          base::Bind(&H264VideoToolboxEncoder::UpdateFrameSize, encoder_,
-                     frame_size));
-      pool_frame_size_ = frame_size;
-      pool_.reset();
-      return nullptr;
-    }
-
-    if (!pool_) {
-      DVLOG(1) << "MaybeCreateFrame: No pixel buffer pool.";
-      return nullptr;
-    }
-
-    // Allocate a pixel buffer from the pool and return a wrapper VideoFrame.
-    base::ScopedCFTypeRef<CVPixelBufferRef> buffer;
-    auto status = CVPixelBufferPoolCreatePixelBuffer(kCFAllocatorDefault, pool_,
-                                                     buffer.InitializeInto());
-    if (status != kCVReturnSuccess) {
-      DLOG(ERROR) << "CVPixelBufferPoolCreatePixelBuffer failed: " << status;
-      return nullptr;
-    }
-
-    DCHECK(buffer);
-    return VideoFrame::WrapCVPixelBuffer(buffer, timestamp);
+  if (media::PIXEL_FORMAT_I420 != format) {
+    DLOG(ERROR) << "Input format not supported= "
+                << media::VideoPixelFormatToString(format);
+    return false;
   }
-
-  void Update(const base::ScopedCFTypeRef<CVPixelBufferPoolRef>& pool,
-              const gfx::Size& frame_size) {
-    base::AutoLock auto_lock(lock_);
-    pool_ = pool;
-    pool_frame_size_ = frame_size;
+  if (media::H264PROFILE_BASELINE != output_profile) {
+    DLOG(ERROR) << "Output profile not supported= "
+                << output_profile;
+    return false;
   }
 
- private:
-  friend class base::RefCountedThreadSafe<VideoFrameFactoryImpl>;
-  ~VideoFrameFactoryImpl() final {}
-
-  base::Lock lock_;
-  base::ScopedCFTypeRef<CVPixelBufferPoolRef> pool_;
-  gfx::Size pool_frame_size_;
+  videotoolbox_glue_ = VideoToolboxGlue::Get();
+  if (!videotoolbox_glue_) {
+    DLOG(ERROR) << "Failed creating VideoToolbox glue.";
+    return false;
+  }
 
-  // Weak back reference to the encoder and the cast envrionment so we can
-  // message the encoder when the frame size changes.
-  const base::WeakPtr<H264VideoToolboxEncoder> encoder_;
-  const scoped_refptr<CastEnvironment> cast_environment_;
+  client_ptr_factory_.reset(new base::WeakPtrFactory<Client>(client));
+  client_ = client_ptr_factory_->GetWeakPtr();
+  input_visible_size_ = input_visible_size;
+  frame_rate_ = kMaxFrameRateNumerator / kMaxFrameRateDenominator;
+  target_bitrate_ = initial_bitrate;
+  bitstream_buffer_size_ = input_visible_size.GetArea();
 
-  DISALLOW_COPY_AND_ASSIGN(VideoFrameFactoryImpl);
-};
-
-class H264VideoToolboxEncoder::VideoFrameFactoryImpl::Proxy
-    : public VideoFrameFactory {
- public:
-  explicit Proxy(
-      const scoped_refptr<VideoFrameFactoryImpl>& video_frame_factory)
-      : video_frame_factory_(video_frame_factory) {
-    DCHECK(video_frame_factory_);
+  if (!encoder_thread_.Start()) {
+    DLOG(ERROR) << "Failed spawning encoder thread.";
+    return false;
   }
+  encoder_thread_task_runner_ = encoder_thread_.task_runner();
 
-  scoped_refptr<VideoFrame> MaybeCreateFrame(
-      const gfx::Size& frame_size,
-      base::TimeDelta timestamp) final {
-    return video_frame_factory_->MaybeCreateFrame(frame_size, timestamp);
+  if (!ResetCompressionSession()) {
+    DLOG(ERROR) << "Failed creating compression session.";
+    return false;
   }
 
- private:
-  ~Proxy() final {}
-
-  const scoped_refptr<VideoFrameFactoryImpl> video_frame_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(Proxy);
-};
-
-// static
-bool H264VideoToolboxEncoder::IsSupported(
-    const VideoSenderConfig& video_config) {
-  return video_config.codec == CODEC_VIDEO_H264 && VideoToolboxGlue::Get();
-}
-
-H264VideoToolboxEncoder::H264VideoToolboxEncoder(
-    const scoped_refptr<CastEnvironment>& cast_environment,
-    const VideoSenderConfig& video_config,
-    const StatusChangeCallback& status_change_cb)
-    : cast_environment_(cast_environment),
-      videotoolbox_glue_(VideoToolboxGlue::Get()),
-      video_config_(video_config),
-      status_change_cb_(status_change_cb),
-      last_frame_id_(kFirstFrameId - 1),
-      encode_next_frame_as_keyframe_(false),
-      power_suspended_(false),
-      weak_factory_(this) {
-  DCHECK(cast_environment_->CurrentlyOn(CastEnvironment::MAIN));
-  DCHECK(!status_change_cb_.is_null());
-
-  OperationalStatus operational_status =
-      H264VideoToolboxEncoder::IsSupported(video_config)
-          ? STATUS_INITIALIZED
-          : STATUS_UNSUPPORTED_CODEC;
-  cast_environment_->PostTask(
-      CastEnvironment::MAIN, FROM_HERE,
-      base::Bind(status_change_cb_, operational_status));
-
-  if (operational_status == STATUS_INITIALIZED) {
-    // Create the shared video frame factory. It persists for the combined
-    // lifetime of the encoder and all video frame factory proxies created by
-    // |CreateVideoFrameFactory| that reference it.
-    video_frame_factory_ =
-        scoped_refptr<VideoFrameFactoryImpl>(new VideoFrameFactoryImpl(
-            weak_factory_.GetWeakPtr(), cast_environment_));
-
-    // Register for power state changes.
-    auto power_monitor = base::PowerMonitor::Get();
-    if (power_monitor) {
-      power_monitor->AddObserver(this);
-      VLOG(1) << "Registered for power state changes.";
-    } else {
-      DLOG(WARNING) << "No power monitor. Process suspension will invalidate "
-                       "the encoder.";
-    }
-  }
+  client_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&Client::RequireBitstreamBuffers, client_, kNumInputBuffers,
+                 input_visible_size_, bitstream_buffer_size_));
+  return true;
 }
 
-H264VideoToolboxEncoder::~H264VideoToolboxEncoder() {
-  DestroyCompressionSession();
+void VTVideoEncodeAccelerator::Encode(
+    const scoped_refptr<media::VideoFrame>& frame,
+    bool force_keyframe) {
+  DVLOG(3) << __FUNCTION__;
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  // If video_frame_factory_ is not null, the encoder registered for power state
-  // changes in the ctor and it must now unregister.
-  if (video_frame_factory_) {
-    auto power_monitor = base::PowerMonitor::Get();
-    if (power_monitor)
-      power_monitor->RemoveObserver(this);
-  }
+  encoder_thread_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&VTVideoEncodeAccelerator::EncodeTask,
+                            base::Unretained(this), frame, force_keyframe));
 }
 
-void H264VideoToolboxEncoder::ResetCompressionSession() {
+void VTVideoEncodeAccelerator::UseOutputBitstreamBuffer(
+    const media::BitstreamBuffer& buffer) {
+  DVLOG(3) << __FUNCTION__ << ": buffer size=" << buffer.size();
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  // Ignore reset requests while power suspended.
-  if (power_suspended_)
+  if (buffer.size() < bitstream_buffer_size_) {
+    DLOG(ERROR) << "Output BitstreamBuffer isn't big enough: " << buffer.size()
+                << " vs. " << bitstream_buffer_size_;
+    client_->NotifyError(kInvalidArgumentError);
     return;
+  }
 
-  // Notify that we're resetting the encoder.
-  cast_environment_->PostTask(
-      CastEnvironment::MAIN, FROM_HERE,
-      base::Bind(status_change_cb_, STATUS_CODEC_REINIT_PENDING));
-
-  // Destroy the current session, if any.
-  DestroyCompressionSession();
-
-  // On OS X, allow the hardware encoder. Don't require it, it does not support
-  // all configurations (some of which are used for testing).
-  base::ScopedCFTypeRef<CFDictionaryRef> encoder_spec;
-#if !defined(OS_IOS)
-  encoder_spec = DictionaryWithKeyValue(
-      videotoolbox_glue_
-          ->kVTVideoEncoderSpecification_EnableHardwareAcceleratedVideoEncoder(),
-      kCFBooleanTrue);
-#endif
-
-  // Force 420v so that clients can easily use these buffers as GPU textures.
-  const int format[] = {
-      CoreVideoGlue::kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange};
-
-  // Keep these attachment settings in-sync with those in ConfigureSession().
-  CFTypeRef attachments_keys[] = {kCVImageBufferColorPrimariesKey,
-                                  kCVImageBufferTransferFunctionKey,
-                                  kCVImageBufferYCbCrMatrixKey};
-  CFTypeRef attachments_values[] = {kCVImageBufferColorPrimaries_ITU_R_709_2,
-                                    kCVImageBufferTransferFunction_ITU_R_709_2,
-                                    kCVImageBufferYCbCrMatrix_ITU_R_709_2};
-  CFTypeRef buffer_attributes_keys[] = {kCVPixelBufferPixelFormatTypeKey,
-                                        kCVBufferPropagatedAttachmentsKey};
-  CFTypeRef buffer_attributes_values[] = {
-      ArrayWithIntegers(format, arraysize(format)).release(),
-      DictionaryWithKeysAndValues(attachments_keys, attachments_values,
-                                  arraysize(attachments_keys)).release()};
-  const base::ScopedCFTypeRef<CFDictionaryRef> buffer_attributes =
-      DictionaryWithKeysAndValues(buffer_attributes_keys,
-                                  buffer_attributes_values,
-                                  arraysize(buffer_attributes_keys));
-  for (auto& v : buffer_attributes_values)
-    CFRelease(v);
-
-  // Create the compression session.
-
-  // Note that the encoder object is given to the compression session as the
-  // callback context using a raw pointer. The C API does not allow us to use a
-  // smart pointer, nor is this encoder ref counted. However, this is still
-  // safe, because we 1) we own the compression session and 2) we tear it down
-  // safely. When destructing the encoder, the compression session is flushed
-  // and invalidated. Internally, VideoToolbox will join all of its threads
-  // before returning to the client. Therefore, when control returns to us, we
-  // are guaranteed that the output callback will not execute again.
-  OSStatus status = videotoolbox_glue_->VTCompressionSessionCreate(
-      kCFAllocatorDefault, frame_size_.width(), frame_size_.height(),
-      CoreMediaGlue::kCMVideoCodecType_H264, encoder_spec, buffer_attributes,
-      nullptr /* compressedDataAllocator */,
-      &H264VideoToolboxEncoder::CompressionCallback,
-      reinterpret_cast<void*>(this), compression_session_.InitializeInto());
-  if (status != noErr) {
-    DLOG(ERROR) << " VTCompressionSessionCreate failed: " << status;
-    // Notify that reinitialization has failed.
-    cast_environment_->PostTask(
-        CastEnvironment::MAIN, FROM_HERE,
-        base::Bind(status_change_cb_, STATUS_CODEC_INIT_FAILED));
+  scoped_ptr<base::SharedMemory> shm(
+      new base::SharedMemory(buffer.handle(), false));
+  if (!shm->Map(buffer.size())) {
+    DLOG(ERROR) << "Failed mapping shared memory.";
+    client_->NotifyError(kPlatformFailureError);
     return;
   }
 
-  // Configure the session (apply session properties based on the current state
-  // of the encoder, experimental tuning and requirements).
-  ConfigureCompressionSession();
-
-  // Update the video frame factory.
-  base::ScopedCFTypeRef<CVPixelBufferPoolRef> pool(
-      videotoolbox_glue_->VTCompressionSessionGetPixelBufferPool(
-          compression_session_),
-      base::scoped_policy::RETAIN);
-  video_frame_factory_->Update(pool, frame_size_);
-
-  // Notify that reinitialization is done.
-  cast_environment_->PostTask(
-      CastEnvironment::MAIN, FROM_HERE,
-      base::Bind(status_change_cb_, STATUS_INITIALIZED));
-}
+  scoped_ptr<BitstreamBufferRef> buffer_ref(
+      new BitstreamBufferRef(buffer.id(), std::move(shm), buffer.size()));
 
-void H264VideoToolboxEncoder::ConfigureCompressionSession() {
-  SetSessionProperty(
-      videotoolbox_glue_->kVTCompressionPropertyKey_ProfileLevel(),
-      videotoolbox_glue_->kVTProfileLevel_H264_Main_AutoLevel());
-  SetSessionProperty(videotoolbox_glue_->kVTCompressionPropertyKey_RealTime(),
-                     true);
-  SetSessionProperty(
-      videotoolbox_glue_->kVTCompressionPropertyKey_AllowFrameReordering(),
-      false);
-  SetSessionProperty(
-      videotoolbox_glue_->kVTCompressionPropertyKey_MaxKeyFrameInterval(), 240);
-  SetSessionProperty(
-      videotoolbox_glue_
-          ->kVTCompressionPropertyKey_MaxKeyFrameIntervalDuration(),
-      240);
-  // TODO(jfroy): implement better bitrate control
-  //              https://crbug.com/425352
-  SetSessionProperty(
-      videotoolbox_glue_->kVTCompressionPropertyKey_AverageBitRate(),
-      (video_config_.min_bitrate + video_config_.max_bitrate) / 2);
-  SetSessionProperty(
-      videotoolbox_glue_->kVTCompressionPropertyKey_ExpectedFrameRate(),
-      video_config_.max_frame_rate);
-  // Keep these attachment settings in-sync with those in Initialize().
-  SetSessionProperty(
-      videotoolbox_glue_->kVTCompressionPropertyKey_ColorPrimaries(),
-      kCVImageBufferColorPrimaries_ITU_R_709_2);
-  SetSessionProperty(
-      videotoolbox_glue_->kVTCompressionPropertyKey_TransferFunction(),
-      kCVImageBufferTransferFunction_ITU_R_709_2);
-  SetSessionProperty(
-      videotoolbox_glue_->kVTCompressionPropertyKey_YCbCrMatrix(),
-      kCVImageBufferYCbCrMatrix_ITU_R_709_2);
-  if (video_config_.max_number_of_video_buffers_used > 0) {
-    SetSessionProperty(
-        videotoolbox_glue_->kVTCompressionPropertyKey_MaxFrameDelayCount(),
-        video_config_.max_number_of_video_buffers_used);
-  }
+  encoder_thread_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&VTVideoEncodeAccelerator::UseOutputBitstreamBufferTask,
+                 base::Unretained(this), base::Passed(&buffer_ref)));
 }
 
-void H264VideoToolboxEncoder::DestroyCompressionSession() {
+void VTVideoEncodeAccelerator::RequestEncodingParametersChange(
+    uint32_t bitrate,
+    uint32_t framerate) {
+  DVLOG(3) << __FUNCTION__ << ": bitrate=" << bitrate
+           << ": framerate=" << framerate;
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  // If the compression session exists, invalidate it. This blocks until all
-  // pending output callbacks have returned and any internal threads have
-  // joined, ensuring no output callback ever sees a dangling encoder pointer.
-  //
-  // Before destroying the compression session, the video frame factory's pool
-  // is updated to null so that no thread will produce new video frames via the
-  // factory until a new compression session is created. The current frame size
-  // is passed to prevent the video frame factory from posting |UpdateFrameSize|
-  // tasks. Indeed, |DestroyCompressionSession| is either called from
-  // |ResetCompressionSession|, in which case a new pool and frame size will be
-  // set, or from callsites that require that there be no compression session
-  // (ex: the dtor).
-  if (compression_session_) {
-    video_frame_factory_->Update(
-        base::ScopedCFTypeRef<CVPixelBufferPoolRef>(nullptr), frame_size_);
-    videotoolbox_glue_->VTCompressionSessionInvalidate(compression_session_);
-    compression_session_.reset();
-  }
+  encoder_thread_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&VTVideoEncodeAccelerator::RequestEncodingParametersChangeTask,
+                 base::Unretained(this), bitrate, framerate));
 }
 
-bool H264VideoToolboxEncoder::EncodeVideoFrame(
-    const scoped_refptr<media::VideoFrame>& video_frame,
-    const base::TimeTicks& reference_time,
-    const FrameEncodedCallback& frame_encoded_callback) {
+void VTVideoEncodeAccelerator::Destroy() {
+  DVLOG(3) << __FUNCTION__;
   DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(!frame_encoded_callback.is_null());
 
-  // Reject empty video frames.
-  const gfx::Size frame_size = video_frame->visible_rect().size();
-  if (frame_size.IsEmpty()) {
-    DVLOG(1) << "Rejecting empty video frame.";
-    return false;
-  }
-
-  // Handle frame size changes. This will reset the compression session.
-  if (frame_size != frame_size_) {
-    DVLOG(1) << "EncodeVideoFrame: Detected frame size change.";
-    UpdateFrameSize(frame_size);
-  }
+  // Cancel all callbacks.
+  client_ptr_factory_.reset();
 
-  // Need a compression session to continue.
-  if (!compression_session_) {
-    DLOG(ERROR) << "No compression session.";
-    return false;
+  if (encoder_thread_.IsRunning()) {
+    encoder_thread_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&VTVideoEncodeAccelerator::DestroyTask,
+                   base::Unretained(this)));
+    encoder_thread_.Stop();
+  } else {
+    DestroyTask();
   }
+}
 
-  // Wrap the VideoFrame in a CVPixelBuffer. In all cases, no data will be
-  // copied. If the VideoFrame was created by this encoder's video frame
-  // factory, then the returned CVPixelBuffer will have been obtained from the
-  // compression session's pixel buffer pool. This will eliminate a copy of the
-  // frame into memory visible by the hardware encoder. The VideoFrame's
-  // lifetime is extended for the lifetime of the returned CVPixelBuffer.
-  auto pixel_buffer = media::WrapVideoFrameInCVPixelBuffer(*video_frame);
-  if (!pixel_buffer) {
-    DLOG(ERROR) << "WrapVideoFrameInCVPixelBuffer failed.";
-    return false;
+void VTVideoEncodeAccelerator::EncodeTask(
+    const scoped_refptr<media::VideoFrame>& frame,
+    bool force_keyframe) {
+  DCHECK(encoder_thread_task_runner_->BelongsToCurrentThread());
+  DCHECK(compression_session_);
+  DCHECK(frame);
+
+  // TODO(emircan): See if we can eliminate a copy here by using
+  // CVPixelBufferPool for the allocation of incoming VideoFrames.
+  base::ScopedCFTypeRef<CVPixelBufferRef> pixel_buffer =
+      media::WrapVideoFrameInCVPixelBuffer(*frame);
+  base::ScopedCFTypeRef<CFDictionaryRef> frame_props =
+      media::video_toolbox::DictionaryWithKeyValue(
+          videotoolbox_glue_->kVTEncodeFrameOptionKey_ForceKeyFrame(),
+          force_keyframe ? kCFBooleanTrue : kCFBooleanFalse);
+
+  base::TimeTicks ref_time;
+  if (!frame->metadata()->GetTimeTicks(
+          media::VideoFrameMetadata::REFERENCE_TIME, &ref_time)) {
+    ref_time = base::TimeTicks::Now();
   }
-
-  // Convert the frame timestamp to CMTime.
   auto timestamp_cm = CoreMediaGlue::CMTimeMake(
-      (reference_time - base::TimeTicks()).InMicroseconds(), USEC_PER_SEC);
-
+      frame->timestamp().InMicroseconds(), USEC_PER_SEC);
   // Wrap information we'll need after the frame is encoded in a heap object.
   // We'll get the pointer back from the VideoToolbox completion callback.
   scoped_ptr<InProgressFrameEncode> request(new InProgressFrameEncode(
-      RtpTimeTicks::FromTimeDelta(video_frame->timestamp(), kVideoFrequency),
-      reference_time, frame_encoded_callback));
-
-  // Build a suitable frame properties dictionary for keyframes.
-  base::ScopedCFTypeRef<CFDictionaryRef> frame_props;
-  if (encode_next_frame_as_keyframe_) {
-    frame_props = DictionaryWithKeyValue(
-        videotoolbox_glue_->kVTEncodeFrameOptionKey_ForceKeyFrame(),
-        kCFBooleanTrue);
-    encode_next_frame_as_keyframe_ = false;
-  }
+      frame->timestamp(), ref_time));
 
-  // Submit the frame to the compression session. The function returns as soon
-  // as the frame has been enqueued.
+  // We can pass the ownership of |request| to the encode callback if
+  // successful. Otherwise let it fall out of scope.
   OSStatus status = videotoolbox_glue_->VTCompressionSessionEncodeFrame(
       compression_session_, pixel_buffer, timestamp_cm,
       CoreMediaGlue::CMTime{0, 0, 0, 0}, frame_props,
-      reinterpret_cast<void*>(request.release()), nullptr);
+      reinterpret_cast<void*>(request.get()), nullptr);
   if (status != noErr) {
     DLOG(ERROR) << " VTCompressionSessionEncodeFrame failed: " << status;
-    return false;
+    NotifyError(kPlatformFailureError);
+  } else {
+    CHECK(request.release());
   }
-
-  return true;
 }
 
-void H264VideoToolboxEncoder::UpdateFrameSize(const gfx::Size& size_needed) {
-  DCHECK(thread_checker_.CalledOnValidThread());
+void VTVideoEncodeAccelerator::UseOutputBitstreamBufferTask(
+    scoped_ptr<BitstreamBufferRef> buffer_ref) {
+  DCHECK(encoder_thread_task_runner_->BelongsToCurrentThread());
 
-  // Our video frame factory posts a task to update the frame size when its
-  // cache of the frame size differs from what the client requested. To avoid
-  // spurious encoder resets, check again here.
-  if (size_needed == frame_size_) {
-    DCHECK(compression_session_);
+  // If there is already EncodeOutput waiting, copy its output first.
+  if (!encoder_output_queue_.empty()) {
+    scoped_ptr<VTVideoEncodeAccelerator::EncodeOutput> encode_output =
+        std::move(encoder_output_queue_.front());
+    encoder_output_queue_.pop_front();
+    ReturnBitstreamBuffer(std::move(encode_output), std::move(buffer_ref));
     return;
   }
 
-  VLOG(1) << "Resetting compression session (for frame size change from "
-          << frame_size_.ToString() << " to " << size_needed.ToString() << ").";
+  bitstream_buffer_queue_.push_back(std::move(buffer_ref));
+}
 
-  // If there is an existing session, finish every pending frame.
-  if (compression_session_) {
-    EmitFrames();
-  }
+void VTVideoEncodeAccelerator::RequestEncodingParametersChangeTask(
+    uint32_t bitrate,
+    uint32_t framerate) {
+  DCHECK(encoder_thread_task_runner_->BelongsToCurrentThread());
 
-  // Store the new frame size.
-  frame_size_ = size_needed;
+  frame_rate_ = framerate > 1 ? framerate : 1;
+  target_bitrate_ = bitrate > 1 ? bitrate : 1;
 
-  // Reset the compression session.
-  ResetCompressionSession();
+  if (!compression_session_) {
+    NotifyError(kPlatformFailureError);
+    return;
+  }
+
+  media::video_toolbox::SessionPropertySetter session_property_setter(
+      compression_session_, videotoolbox_glue_);
+  // TODO(emircan): See crbug.com/425352.
+  bool rv = session_property_setter.Set(
+      videotoolbox_glue_->kVTCompressionPropertyKey_AverageBitRate(),
+      target_bitrate_);
+  rv &= session_property_setter.Set(
+      videotoolbox_glue_->kVTCompressionPropertyKey_ExpectedFrameRate(),
+      frame_rate_);
+  rv &= session_property_setter.Set(
+      videotoolbox_glue_->kVTCompressionPropertyKey_DataRateLimits(),
+      media::video_toolbox::ArrayWithIntegerAndFloat(
+          target_bitrate_ / kBitsPerByte, 1.0f));
+  DLOG_IF(ERROR, !rv) << "Couldn't change session encoding parameters.";
 }
 
-void H264VideoToolboxEncoder::SetBitRate(int /*new_bit_rate*/) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  // VideoToolbox does not seem to support bitrate reconfiguration.
+void VTVideoEncodeAccelerator::DestroyTask() {
+  DCHECK(thread_checker_.CalledOnValidThread() ||
+         (encoder_thread_.IsRunning() &&
+          encoder_thread_task_runner_->BelongsToCurrentThread()));
+
+  // Cancel all encoder thread callbacks.
+  encoder_task_weak_factory_.InvalidateWeakPtrs();
+
+  // This call blocks until all pending frames are flushed out.
+  DestroyCompressionSession();
 }
 
-void H264VideoToolboxEncoder::GenerateKeyFrame() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  encode_next_frame_as_keyframe_ = true;
+void VTVideoEncodeAccelerator::NotifyError(
+    media::VideoEncodeAccelerator::Error error) {
+  DCHECK(encoder_thread_task_runner_->BelongsToCurrentThread());
+  client_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&Client::NotifyError, client_, error));
 }
 
-scoped_ptr<VideoFrameFactory>
-H264VideoToolboxEncoder::CreateVideoFrameFactory() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  return scoped_ptr<VideoFrameFactory>(
-      new VideoFrameFactoryImpl::Proxy(video_frame_factory_));
+// static
+void VTVideoEncodeAccelerator::CompressionCallback(void* encoder_opaque,
+                                                   void* request_opaque,
+                                                   OSStatus status,
+                                                   VTEncodeInfoFlags info,
+                                                   CMSampleBufferRef sbuf) {
+  // This function may be called asynchronously, on a different thread from the
+  // one that calls VTCompressionSessionEncodeFrame.
+  DVLOG(3) << __FUNCTION__;
+
+  auto encoder = reinterpret_cast<VTVideoEncodeAccelerator*>(encoder_opaque);
+  DCHECK(encoder);
+
+  // Release InProgressFrameEncode, since we don't have support to return
+  // timestamps at this point.
+  scoped_ptr<InProgressFrameEncode> request(
+      reinterpret_cast<InProgressFrameEncode*>(request_opaque));
+  request.reset();
+
+  // EncodeOutput holds onto CMSampleBufferRef when posting task between
+  // threads.
+  scoped_ptr<EncodeOutput> encode_output(new EncodeOutput(info, sbuf));
+
+  // This method is NOT called on |encoder_thread_|, so we still need to
+  // post a task back to it to do work.
+  encoder->encoder_thread_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&VTVideoEncodeAccelerator::CompressionCallbackTask,
+                            encoder->encoder_weak_ptr_, status,
+                            base::Passed(&encode_output)));
 }
 
-void H264VideoToolboxEncoder::EmitFrames() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  if (!compression_session_)
-    return;
+void VTVideoEncodeAccelerator::CompressionCallbackTask(
+    OSStatus status,
+    scoped_ptr<EncodeOutput> encode_output) {
+  DCHECK(encoder_thread_task_runner_->BelongsToCurrentThread());
 
-  OSStatus status = videotoolbox_glue_->VTCompressionSessionCompleteFrames(
-      compression_session_, CoreMediaGlue::CMTime{0, 0, 0, 0});
   if (status != noErr) {
-    DLOG(ERROR) << " VTCompressionSessionCompleteFrames failed: " << status;
+    DLOG(ERROR) << " encode failed: " << status;
+    NotifyError(kPlatformFailureError);
+    return;
   }
-}
 
-void H264VideoToolboxEncoder::OnSuspend() {
-  VLOG(1)
-      << "OnSuspend: Emitting all frames and destroying compression session.";
-  EmitFrames();
-  DestroyCompressionSession();
-  power_suspended_ = true;
+  // If there isn't any BitstreamBuffer to copy into, add it to a queue for
+  // later use.
+  if (bitstream_buffer_queue_.empty()) {
+    encoder_output_queue_.push_back(std::move(encode_output));
+    return;
+  }
+
+  scoped_ptr<VTVideoEncodeAccelerator::BitstreamBufferRef> buffer_ref =
+      std::move(bitstream_buffer_queue_.front());
+  bitstream_buffer_queue_.pop_front();
+  ReturnBitstreamBuffer(std::move(encode_output), std::move(buffer_ref));
 }
 
-void H264VideoToolboxEncoder::OnResume() {
-  power_suspended_ = false;
+void VTVideoEncodeAccelerator::ReturnBitstreamBuffer(
+    scoped_ptr<EncodeOutput> encode_output,
+    scoped_ptr<VTVideoEncodeAccelerator::BitstreamBufferRef> buffer_ref) {
+  DVLOG(3) << __FUNCTION__;
+  DCHECK(encoder_thread_task_runner_->BelongsToCurrentThread());
 
-  // Reset the compression session only if the frame size is not zero (which
-  // will obviously fail). It is possible for the frame size to be zero if no
-  // frame was submitted for encoding or requested from the video frame factory
-  // before suspension.
-  if (!frame_size_.IsEmpty()) {
-    VLOG(1) << "OnResume: Resetting compression session.";
-    ResetCompressionSession();
+  if (encode_output->info & VideoToolboxGlue::kVTEncodeInfo_FrameDropped) {
+    DVLOG(2) << " frame dropped";
+    client_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&Client::BitstreamBufferReady, client_,
+                              buffer_ref->id, 0, false));
+    return;
   }
-}
 
-bool H264VideoToolboxEncoder::SetSessionProperty(CFStringRef key,
-                                                 int32_t value) {
-  base::ScopedCFTypeRef<CFNumberRef> cfvalue(
-      CFNumberCreate(nullptr, kCFNumberSInt32Type, &value));
-  return videotoolbox_glue_->VTSessionSetProperty(compression_session_, key,
-                                                  cfvalue) == noErr;
-}
+  auto sample_attachments = static_cast<CFDictionaryRef>(CFArrayGetValueAtIndex(
+      CoreMediaGlue::CMSampleBufferGetSampleAttachmentsArray(
+          encode_output->sample_buffer.get(), true),
+      0));
+  const bool keyframe =
+      !CFDictionaryContainsKey(sample_attachments,
+                               CoreMediaGlue::kCMSampleAttachmentKey_NotSync());
+
+  size_t used_buffer_size = 0;
+  const bool copy_rv = media::video_toolbox::CopySampleBufferToAnnexBBuffer(
+      encode_output->sample_buffer.get(), keyframe, buffer_ref->size,
+      reinterpret_cast<char*>(buffer_ref->shm->memory()), &used_buffer_size);
+  if (!copy_rv) {
+    DLOG(ERROR) << "Cannot copy output from SampleBuffer to AnnexBBuffer.";
+    used_buffer_size = 0;
+  }
 
-bool H264VideoToolboxEncoder::SetSessionProperty(CFStringRef key, bool value) {
-  CFBooleanRef cfvalue = (value) ? kCFBooleanTrue : kCFBooleanFalse;
-  return videotoolbox_glue_->VTSessionSetProperty(compression_session_, key,
-                                                  cfvalue) == noErr;
+  client_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&Client::BitstreamBufferReady, client_,
+                            buffer_ref->id, used_buffer_size, keyframe));
 }
 
-bool H264VideoToolboxEncoder::SetSessionProperty(CFStringRef key,
-                                                 CFStringRef value) {
-  return videotoolbox_glue_->VTSessionSetProperty(compression_session_, key,
-                                                  value) == noErr;
+bool VTVideoEncodeAccelerator::ResetCompressionSession() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  DestroyCompressionSession();
+
+  CFTypeRef attributes_keys[] = {
+    kCVPixelBufferOpenGLCompatibilityKey,
+    kCVPixelBufferIOSurfacePropertiesKey,
+    kCVPixelBufferPixelFormatTypeKey
+  };
+  const int format[] = {
+      CoreVideoGlue::kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange};
+  CFTypeRef attributes_values[] = {
+      kCFBooleanTrue,
+      media::video_toolbox::DictionaryWithKeysAndValues(nullptr, nullptr, 0)
+          .release(),
+      media::video_toolbox::ArrayWithIntegers(format, arraysize(format))
+          .release()};
+  const base::ScopedCFTypeRef<CFDictionaryRef> attributes =
+      media::video_toolbox::DictionaryWithKeysAndValues(
+          attributes_keys, attributes_values, arraysize(attributes_keys));
+  for (auto& v : attributes_values)
+    CFRelease(v);
+
+  bool session_rv =
+      CreateCompressionSession(attributes, input_visible_size_, false);
+  if (!session_rv) {
+    DestroyCompressionSession();
+    return false;
+  }
+
+  const bool configure_rv = ConfigureCompressionSession();
+  if (configure_rv)
+    RequestEncodingParametersChange(target_bitrate_, frame_rate_);
+  return configure_rv;
 }
 
-void H264VideoToolboxEncoder::CompressionCallback(void* encoder_opaque,
-                                                  void* request_opaque,
-                                                  OSStatus status,
-                                                  VTEncodeInfoFlags info,
-                                                  CMSampleBufferRef sbuf) {
-  auto encoder = reinterpret_cast<H264VideoToolboxEncoder*>(encoder_opaque);
-  const scoped_ptr<InProgressFrameEncode> request(
-      reinterpret_cast<InProgressFrameEncode*>(request_opaque));
-  bool keyframe = false;
-  bool has_frame_data = false;
+bool VTVideoEncodeAccelerator::CreateCompressionSession(
+    base::ScopedCFTypeRef<CFDictionaryRef> attributes,
+    const gfx::Size& input_size,
+    bool require_hw_encoding) {
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  if (status != noErr) {
-    DLOG(ERROR) << " encoding failed: " << status;
-    encoder->cast_environment_->PostTask(
-        CastEnvironment::MAIN, FROM_HERE,
-        base::Bind(encoder->status_change_cb_, STATUS_CODEC_RUNTIME_ERROR));
-  } else if ((info & VideoToolboxGlue::kVTEncodeInfo_FrameDropped)) {
-    DVLOG(2) << " frame dropped";
+  std::vector<CFTypeRef> encoder_keys;
+  std::vector<CFTypeRef> encoder_values;
+  if (require_hw_encoding) {
+    encoder_keys.push_back(videotoolbox_glue_
+      ->kVTVideoEncoderSpecification_RequireHardwareAcceleratedVideoEncoder());
+    encoder_values.push_back(kCFBooleanTrue);
   } else {
-    auto sample_attachments =
-        static_cast<CFDictionaryRef>(CFArrayGetValueAtIndex(
-            CoreMediaGlue::CMSampleBufferGetSampleAttachmentsArray(sbuf, true),
-            0));
-
-    // If the NotSync key is not present, it implies Sync, which indicates a
-    // keyframe (at least I think, VT documentation is, erm, sparse). Could
-    // alternatively use kCMSampleAttachmentKey_DependsOnOthers == false.
-    keyframe = !CFDictionaryContainsKey(
-                   sample_attachments,
-                   CoreMediaGlue::kCMSampleAttachmentKey_NotSync());
-    has_frame_data = true;
+    encoder_keys.push_back(videotoolbox_glue_
+        ->kVTVideoEncoderSpecification_EnableHardwareAcceleratedVideoEncoder());
+    encoder_values.push_back(kCFBooleanTrue);
   }
+  base::ScopedCFTypeRef<CFDictionaryRef> encoder_spec =
+      media::video_toolbox::DictionaryWithKeysAndValues(
+          encoder_keys.data(), encoder_values.data(), encoder_keys.size());
 
-  // Increment the encoder-scoped frame id and assign the new value to this
-  // frame. VideoToolbox calls the output callback serially, so this is safe.
-  const uint32_t frame_id = ++encoder->last_frame_id_;
-
-  scoped_ptr<SenderEncodedFrame> encoded_frame(new SenderEncodedFrame());
-  encoded_frame->frame_id = frame_id;
-  encoded_frame->reference_time = request->reference_time;
-  encoded_frame->rtp_timestamp = request->rtp_timestamp;
-  if (keyframe) {
-    encoded_frame->dependency = EncodedFrame::KEY;
-    encoded_frame->referenced_frame_id = frame_id;
-  } else {
-    encoded_frame->dependency = EncodedFrame::DEPENDENT;
-    // H.264 supports complex frame reference schemes (multiple reference
-    // frames, slice references, backward and forward references, etc). Cast
-    // doesn't support the concept of forward-referencing frame dependencies or
-    // multiple frame dependencies; so pretend that all frames are only
-    // decodable after their immediately preceding frame is decoded. This will
-    // ensure a Cast receiver only attempts to decode the frames sequentially
-    // and in order. Furthermore, the encoder is configured to never use forward
-    // references (see |kVTCompressionPropertyKey_AllowFrameReordering|). There
-    // is no way to prevent multiple reference frames.
-    encoded_frame->referenced_frame_id = frame_id - 1;
+  // Create the compression session.
+  // Note that the encoder object is given to the compression session as the
+  // callback context using a raw pointer. The C API does not allow us to use a
+  // smart pointer, nor is this encoder ref counted. However, this is still
+  // safe, because we 1) we own the compression session and 2) we tear it down
+  // safely. When destructing the encoder, the compression session is flushed
+  // and invalidated. Internally, VideoToolbox will join all of its threads
+  // before returning to the client. Therefore, when control returns to us, we
+  // are guaranteed that the output callback will not execute again.
+  OSStatus status = videotoolbox_glue_->VTCompressionSessionCreate(
+      kCFAllocatorDefault,
+      input_size.width(),
+      input_size.height(),
+      CoreMediaGlue::kCMVideoCodecType_H264,
+      encoder_spec,
+      attributes,
+      nullptr /* compressedDataAllocator */,
+      &VTVideoEncodeAccelerator::CompressionCallback,
+      reinterpret_cast<void*>(this),
+      compression_session_.InitializeInto());
+  if (status != noErr) {
+    DLOG(ERROR) << " VTCompressionSessionCreate failed: " << status;
+    return false;
   }
+  DVLOG(3) << " VTCompressionSession created with HW encode: "
+           << require_hw_encoding << ", input size=" << input_size.ToString();
+  return true;
+}
 
-  if (has_frame_data)
-    CopySampleBufferToAnnexBBuffer(sbuf, &encoded_frame->data, keyframe);
+bool VTVideoEncodeAccelerator::ConfigureCompressionSession() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(compression_session_);
 
-  // TODO(miu): Compute and populate the |deadline_utilization| and
-  // |lossy_utilization| performance metrics in |encoded_frame|.
+  media::video_toolbox::SessionPropertySetter session_property_setter(
+      compression_session_, videotoolbox_glue_);
+  bool rv = true;
+  rv &= session_property_setter.Set(
+      videotoolbox_glue_->kVTCompressionPropertyKey_ProfileLevel(),
+      videotoolbox_glue_->kVTProfileLevel_H264_Baseline_AutoLevel());
+  rv &= session_property_setter.Set(
+      videotoolbox_glue_->kVTCompressionPropertyKey_RealTime(), true);
+  rv &= session_property_setter.Set(
+      videotoolbox_glue_->kVTCompressionPropertyKey_AllowFrameReordering(),
+      false);
+  DLOG_IF(ERROR, !rv) << " Setting session property failed.";
+  return rv;
+}
 
-  encoded_frame->encode_completion_time =
-      encoder->cast_environment_->Clock()->NowTicks();
-  encoder->cast_environment_->PostTask(
-      CastEnvironment::MAIN, FROM_HERE,
-      base::Bind(request->frame_encoded_callback,
-                 base::Passed(&encoded_frame)));
+void VTVideoEncodeAccelerator::DestroyCompressionSession() {
+  DCHECK(thread_checker_.CalledOnValidThread() ||
+         (encoder_thread_.IsRunning() &&
+          encoder_thread_task_runner_->BelongsToCurrentThread()));
+
+  if (compression_session_) {
+    videotoolbox_glue_->VTCompressionSessionInvalidate(compression_session_);
+    compression_session_.reset();
+  }
 }
 
-}  // namespace cast
-}  // namespace media
+} // namespace content