[Cast] Size-Adaptable platform video encoders.

media/cast/sender/size_adaptable_video_encoder_base.h

+// Copyright 2015 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.
+
+#ifndef MEDIA_CAST_SENDER_SIZE_ADAPTABLE_VIDEO_ENCODER_BASE_H_
+#define MEDIA_CAST_SENDER_SIZE_ADAPTABLE_VIDEO_ENCODER_BASE_H_
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "media/cast/cast_config.h"
+#include "media/cast/cast_environment.h"
+#include "media/cast/sender/video_encoder.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace media {
+namespace cast {
+
+// Creates and owns a VideoEncoder instance.  The owned instance is an
+// implementation that does not support changing frame sizes, and so
+// SizeAdaptableVideoEncoderBase acts as a proxy to automatically detect when
+// the owned instance should be replaced with one that can handle the new frame
+// size.
+class SizeAdaptableVideoEncoderBase : public VideoEncoder {
+ public:
+  SizeAdaptableVideoEncoderBase(
+      const scoped_refptr<CastEnvironment>& cast_environment,
+      const VideoSenderConfig& video_config,
+      const StatusChangeCallback& status_change_cb);
+
+  ~SizeAdaptableVideoEncoderBase() override;
+
+  // VideoEncoder implementation.
+  bool EncodeVideoFrame(
+      const scoped_refptr<media::VideoFrame>& video_frame,
+      const base::TimeTicks& reference_time,
+      const FrameEncodedCallback& frame_encoded_callback) override;
+  void SetBitRate(int new_bit_rate) override;
+  void GenerateKeyFrame() override;
+  void LatestFrameIdToReference(uint32 frame_id) override;
+  scoped_ptr<VideoFrameFactory> CreateVideoFrameFactory() override;
+  void EmitFrames() override;
+
+ protected:
+  // Accessors for subclasses.
+  CastEnvironment* cast_environment() const {
+    return cast_environment_.get();
+  }
+  const VideoSenderConfig& video_config() const {
+    return video_config_;
+  }
+  const gfx::Size& next_encoder_frame_size() const {
+    return next_encoder_frame_size_;
+  }
+  uint32 last_frame_id() const {
+    return last_frame_id_;
+  }
+
+  // Returns a callback that calls OnEncoderStatusChange().

[hubbe, 2015/02/11 00:47:54]

Why not just make OnEncoderStatusChange() protected?

[miu, 2015/02/11 02:14:24]

I didn't want to expose the weak pointer invalidation to subclasses.  I added a
comment about when the callback would be canceled and why.

+  StatusChangeCallback CreateEncoderStatusChangeCallback();
+
+  // Overridden by subclasses to provide the underlying encoder implementation.
+  virtual scoped_ptr<VideoEncoder> CreateReplacementEncoder() = 0;

[hubbe, 2015/02/11 00:47:54]

Wouldn't this also create the initial encoder?
(Shouldn't it just be called CreateEncoder() ?)

[miu, 2015/02/11 02:14:24]

Done.

+
+  // Overridden by subclasses to perform additional steps when
+  // |replacement_encoder| becomes the active encoder.
+  virtual void OnEncoderReplaced(VideoEncoder* replacement_encoder);
+
+  // Overridden by subclasses to perform additional steps before/after the
+  // current encoder is destroyed.
+  virtual void DestroyCurrentEncoder();
+
+ private:
+  // Create and initialize a replacement video encoder, if this not already
+  // in-progress.  The replacement will call back to OnEncoderStatusChange()
+  // with success/fail status, and |current_encoder_| will be set there.
+  void MaybeSpawnReplacementEncoder(const gfx::Size& size_needed);
+
+  // Called when a status change is received from an encoder.
+  void OnEncoderStatusChange(OperationalStatus status);
+
+  // Called by the |current_encoder_| with the next EncodedFrame.
+  void OnEncodedVideoFrame(const FrameEncodedCallback& frame_encoded_callback,
+                           scoped_ptr<EncodedFrame> encoded_frame);
+
+  const scoped_refptr<CastEnvironment> cast_environment_;
+
+  // This is not const since |video_config_.starting_bitrate| is modified by
+  // SetBitRate(), for when a replacement encoder is spawned.
+  VideoSenderConfig video_config_;
+
+  // Run whenever the underlying encoder reports a status change.
+  const StatusChangeCallback status_change_cb_;
+
+  // The underlying platform video encoder and current frame size.
+  scoped_ptr<VideoEncoder> current_encoder_;

[hubbe, 2015/02/11 00:47:54]

Maybe make a struct which contains an encoder and it's size?

[miu, 2015/02/11 02:14:24]

Eliminated the "next_encoder" stuff, as discussed.

+  gfx::Size current_encoder_frame_size_;
+
+  // The replacement encoder currently being initialized, but not yet ready for
+  // use.
+  scoped_ptr<VideoEncoder> next_encoder_;

[hubbe, 2015/02/11 00:47:54]

Do we really need this?
As far as i can tell, we never actually have two encoders at the same time.

[miu, 2015/02/11 02:14:24]

Done.

+  gfx::Size next_encoder_frame_size_;
+
+  // The number of frames in |current_encoder_|'s pipeline.
+  int frames_in_encoder_;
+
+  // The ID of the last frame that was emitted from |current_encoder_|.
+  uint32 last_frame_id_;
+
+  // NOTE: Weak pointers must be invalidated before all other member variables.
+  base::WeakPtrFactory<SizeAdaptableVideoEncoderBase> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SizeAdaptableVideoEncoderBase);
+};
+
+}  // namespace cast
+}  // namespace media
+
+#endif  // MEDIA_CAST_SENDER_SIZE_ADAPTABLE_VIDEO_ENCODER_BASE_H_