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..6d90e9f234e2f944da9cfa3f77fa43dc05c17c55 100644
--- a/media/cast/sender/h264_vt_encoder.cc
+++ b/content/common/gpu/media/vt_video_encode_accelerator_mac.cc
@@ -1,769 +1,519 @@
-// 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;
-  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) {}
-};
-
-base::ScopedCFTypeRef<CFDictionaryRef>
-DictionaryWithKeysAndValues(CFTypeRef* keys, CFTypeRef* values, size_t size) {
-  return base::ScopedCFTypeRef<CFDictionaryRef>(CFDictionaryCreate(
-      kCFAllocatorDefault, keys, values, size, &kCFTypeDictionaryKeyCallBacks,
-      &kCFTypeDictionaryValueCallBacks));
-}
+// Subjectively chosen.
+// TODO(emircan): Check if we can find the actual system capabilities via
+// creating VTCompressionSessions with varying requirements.
+// See crbug.com/584784.
+const size_t kNumInputBuffers = 3;
+const size_t kMaxFrameRateNumerator = 30;
+const size_t kMaxFrameRateDenominator = 1;
+const size_t kMaxResolutionWidth = 4096;
+const size_t kMaxResolutionHeight = 2160;
+const size_t kBitsPerByte = 8;
 
-base::ScopedCFTypeRef<CFDictionaryRef> DictionaryWithKeyValue(CFTypeRef key,
-                                                              CFTypeRef value) {
-  CFTypeRef keys[1] = {key};
-  CFTypeRef values[1] = {value};
-  return DictionaryWithKeysAndValues(keys, values, 1);
-}
+}  // namespace
 
-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::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;
 
-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(InProgressFrameEncode);
+};
 
-// 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;
-  }
+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;
 
-  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;
-    }
-  }
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(EncodeOutput);
+};
 
-  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);
-    }
-  }
+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;
 
-  // 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;
-    }
-  }
-
-  // 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;
-  }
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(BitstreamBufferRef);
+};
 
-  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();
-  }
+VTVideoEncodeAccelerator::VTVideoEncodeAccelerator()
+    : client_task_runner_(base::ThreadTaskRunnerHandle::Get()),
+      encoder_thread_("VTEncoderThread"),
+      weak_this_factory_(this) {
 }
 
-}  // namespace
+VTVideoEncodeAccelerator::~VTVideoEncodeAccelerator() {
+  DVLOG(3) << __FUNCTION__;
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-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;
-    }
+  Destroy();
+}

[miu, 2016/03/08 22:36:05]

For sanity, after the Destroy() call here, consider adding:

  DCHECK(!encoder_thread_.IsRunning());
  DCHECK(!weak_this_factory_.HasWeakPtrs());

(to be sure the encoder thread and all outstanding tasks have been
stopped/canceled)

[emircan, 2016/03/09 01:13:35]

Done.

 
-    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;
-    }
+media::VideoEncodeAccelerator::SupportedProfiles
+VTVideoEncodeAccelerator::GetSupportedProfiles() {
+  DVLOG(3) << __FUNCTION__;
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-    if (!pool_) {
-      DVLOG(1) << "MaybeCreateFrame: No pixel buffer pool.";
-      return nullptr;
-    }
+  SupportedProfiles profiles;
+  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;
+}
 
-    // 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;
-    }
+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);
 
-    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_;
-
-  // 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_;
+  videotoolbox_glue_ = VideoToolboxGlue::Get();
+  if (!videotoolbox_glue_) {
+    DLOG(ERROR) << "Failed creating VideoToolbox glue";
+    return false;
+  }
 
-  DISALLOW_COPY_AND_ASSIGN(VideoFrameFactoryImpl);
-};
+  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();
 
-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 (!ResetCompressionSession()) {
+    DLOG(ERROR) << "Failed creating compression session";
+    return false;
   }
 
-  scoped_refptr<VideoFrame> MaybeCreateFrame(
-      const gfx::Size& frame_size,
-      base::TimeDelta timestamp) final {
-    return video_frame_factory_->MaybeCreateFrame(frame_size, timestamp);
+  if (!encoder_thread_.Start()) {
+    DLOG(ERROR) << "Failed spawning encoder thread";
+    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_.message_loop()->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));
+  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;
+  }
 
-  // Destroy the current session, if any.
-  DestroyCompressionSession();
+  scoped_ptr<BitstreamBufferRef> buffer_ref(
+      new BitstreamBufferRef(buffer.id(), std::move(shm), buffer.size()));
 
-  // 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};
+  encoder_thread_.message_loop()->PostTask(
+        FROM_HERE,
+        base::Bind(&VTVideoEncodeAccelerator::UseOutputBitstreamBufferTask,
+                   base::Unretained(this),
+                   base::Passed(&buffer_ref)));
+}
 
-  // 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);
+void VTVideoEncodeAccelerator::RequestEncodingParametersChange(
+    uint32_t bitrate,
+    uint32_t framerate) {
+  DVLOG(3) << __FUNCTION__ << ": bitrate=" << bitrate
+           << ": framerate=" << framerate;
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  // Create the compression session.
+  frame_rate_ = framerate > 1 ? framerate : 1;
+  target_bitrate_ = bitrate > 1 ? bitrate : 1;
 
-  // 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));
+  if (!compression_session_) {
+    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));
-}
-
-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(
+  media::video_toolbox::SessionPropertySetter session_property_setter(
+      compression_session_, videotoolbox_glue_);
+  // TODO(emircan): See crbug.com/425352.
+  bool rv = session_property_setter.SetSessionProperty(
       videotoolbox_glue_->kVTCompressionPropertyKey_AverageBitRate(),
-      (video_config_.min_bitrate + video_config_.max_bitrate) / 2);
-  SetSessionProperty(
+      target_bitrate_);
+  rv &= session_property_setter.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);
-  }
-}
-
-void H264VideoToolboxEncoder::DestroyCompressionSession() {
-  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();
-  }
+      frame_rate_);
+  rv &= session_property_setter.SetSessionProperty(
+      videotoolbox_glue_->kVTCompressionPropertyKey_DataRateLimits(),
+      media::video_toolbox::ArrayWithIntegerAndFloat(
+          target_bitrate_ / kBitsPerByte, 1.0f));
+  DLOG_IF(ERROR, !rv) << "Couldn't change session encoding parameters.";
 }
 
-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();

[miu, 2016/03/08 21:27:41]

This is an illegal operation.  The WeakPtrs being dereferenced on the "client
task" thread must always be invalidated on that same thread as well.  Otherwise,
there could be code executing concurrently that has already null-checked the
WeakPtr but still assumes the object is alive.

Hmm...This is a really complex threading model here.  IMO, the simplest solution
is not to access |client_| via a WeakPtr.  Instead, store it as a raw pointer
(in Initialize()) and null it out (in Destroy().  Then, for all read-write
access and calls into the client's methods, always be holding a base::Lock. 
And, always null-check |client_|, of course, since tasks can run after Destroy()
is called.

[miu, 2016/03/08 22:36:05]

Never mind.  My misunderstanding.  We discussed this off-line (it's the same
thread).

 
-  // Need a compression session to continue.
-  if (!compression_session_) {
-    DLOG(ERROR) << "No compression session.";
-    return false;
+  if (encoder_thread_.IsRunning()) {
+    encoder_thread_.message_loop()->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.
   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);
   if (status != noErr) {
     DLOG(ERROR) << " VTCompressionSessionEncodeFrame failed: " << status;
-    return false;
+    NotifyError(kPlatformFailureError);
   }
-
-  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::DestroyTask() {
+  // This thread runs on |encoder_thread_| if it is alive, otherwise on GPU
+  // child thread.
 
-  // Store the new frame size.
-  frame_size_ = size_needed;
+  // Cancel all callbacks.

[miu, 2016/03/08 22:36:05]

nit: Cancel all encoder thread callbacks.

[emircan, 2016/03/09 01:13:35]

Done.

+  weak_this_factory_.InvalidateWeakPtrs();

[miu, 2016/03/08 22:36:05]

naming nit: Instead of weak_this_factory_, how about encoder_task_weak_factory_?
 That would make it clear to the reader that these WeakPtrs are being used only
for encoder tasks on the encode thread.

[emircan, 2016/03/09 01:13:35]

Done.

 
-  // Reset the compression session.
-  ResetCompressionSession();
+  // This call blocks until all pending frames are flushed out.
+  DestroyCompressionSession();
 }
 
-void H264VideoToolboxEncoder::SetBitRate(int /*new_bit_rate*/) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  // VideoToolbox does not seem to support bitrate reconfiguration.
+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));
 }
 
-void H264VideoToolboxEncoder::GenerateKeyFrame() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  encode_next_frame_as_keyframe_ = true;
+// 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->weak_this_factory_.GetWeakPtr(), status,
+                            base::Passed(&encode_output)));
 }
 
-scoped_ptr<VideoFrameFactory>
-H264VideoToolboxEncoder::CreateVideoFrameFactory() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  return scoped_ptr<VideoFrameFactory>(
-      new VideoFrameFactoryImpl::Proxy(video_frame_factory_));
-}
+void VTVideoEncodeAccelerator::CompressionCallbackTask(
+    OSStatus status,
+    scoped_ptr<EncodeOutput> encode_output) {
+  DCHECK(encoder_thread_.task_runner()->BelongsToCurrentThread());
 
-void H264VideoToolboxEncoder::EmitFrames() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  if (!compression_session_)
+  if (status != noErr) {
+    DLOG(ERROR) << " encode failed: " << status;
+    NotifyError(kPlatformFailureError);
     return;
+  }
 
-  OSStatus status = videotoolbox_glue_->VTCompressionSessionCompleteFrames(
-      compression_session_, CoreMediaGlue::CMTime{0, 0, 0, 0});
-  if (status != noErr) {
-    DLOG(ERROR) << " VTCompressionSessionCompleteFrames failed: " << status;
+  // 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;
   }
-}
 
-void H264VideoToolboxEncoder::OnSuspend() {
-  VLOG(1)
-      << "OnSuspend: Emitting all frames and destroying compression session.";
-  EmitFrames();
-  DestroyCompressionSession();
-  power_suspended_ = true;
+  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, true);
+  if (!session_rv) {
+    // Try creating session again without forcing HW encode.
+    DestroyCompressionSession();
+    session_rv = CreateCompressionSession(attributes, false);
+    if (!session_rv) {
+      DestroyCompressionSession();
+      return false;
+    }
+  }
+
+  const bool configure_rv = ConfigureCompressionSession();
+  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,
+    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";
-  } 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;
+  std::vector<CFTypeRef> encoder_keys;
+  std::vector<CFTypeRef> encoder_values;
+  encoder_keys.push_back(videotoolbox_glue_
+        ->kVTVideoEncoderSpecification_EnableHardwareAcceleratedVideoEncoder());
+  encoder_values.push_back(kCFBooleanTrue);
+
+  if (require_hw_encoding) {
+    encoder_keys.push_back(
+        videotoolbox_glue_
+      ->kVTVideoEncoderSpecification_RequireHardwareAcceleratedVideoEncoder());
+    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_visible_size_.width(),
+      input_visible_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;
+  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.SetSessionProperty(
+      videotoolbox_glue_->kVTCompressionPropertyKey_ProfileLevel(),
+      videotoolbox_glue_->kVTProfileLevel_H264_Baseline_AutoLevel());
+  rv &= session_property_setter.SetSessionProperty(
+      videotoolbox_glue_->kVTCompressionPropertyKey_RealTime(), true);
+  rv &= session_property_setter.SetSessionProperty(
+      videotoolbox_glue_->kVTCompressionPropertyKey_AllowFrameReordering(),
+      false);
+  DLOG_IF(ERROR, !rv) << " SetSessionProperty 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() {
+  // This method may be called on |encoder thread| or GPU child thread.
+
+  if (compression_session_) {
+    videotoolbox_glue_->VTCompressionSessionInvalidate(compression_session_);
+    compression_session_.reset();
+  }
 }
 
-}  // namespace cast
-}  // namespace media
+} // namespace content