iOS: Optimize video scaling and cropping

webrtc/common_video/include/corevideo_frame_buffer.h

 /*
  *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_COMMON_VIDEO_INCLUDE_COREVIDEO_FRAME_BUFFER_H_
 #define WEBRTC_COMMON_VIDEO_INCLUDE_COREVIDEO_FRAME_BUFFER_H_
 
 #include <CoreVideo/CoreVideo.h>
 
+#include <vector>
+
 #include "webrtc/common_video/include/video_frame_buffer.h"
 
 namespace webrtc {
 
 class CoreVideoFrameBuffer : public NativeHandleBuffer {
  public:
   explicit CoreVideoFrameBuffer(CVPixelBufferRef pixel_buffer);
+  CoreVideoFrameBuffer(CVPixelBufferRef pixel_buffer,
+                       int adapted_width,
+                       int adapted_height,
+                       int crop_width,
+                       int crop_height,
+                       int crop_x,
+                       int crop_y);
   ~CoreVideoFrameBuffer() override;
 
   rtc::scoped_refptr<VideoFrameBuffer> NativeToI420Buffer() override;
+  // Returns true if the internal pixel buffer needs to be cropped.
+  bool RequiresCropping() const;
+  // Crop and scales the internal pixel buffer to the output pixel buffer. The
+  // tmp buffer is used for intermediary splitting the UV channels. This
+  // function returns true if successful.
+  bool CropAndScaleTo(std::vector<uint8_t>* tmp_buffer,
+                      CVPixelBufferRef output_pixel_buffer) const;
 
  private:
   CVPixelBufferRef pixel_buffer_;
+  const int buffer_width_;

[tkchin_webrtc, 2016/10/19 00:48:32]

how is buffer width different from width/height of NativeHandleBuffer?

[magjed_webrtc, 2016/10/19 13:19:34]

I agree this is a bit confusing, but I don't see how I can easily make it
clearer. It works like this: buffer_width/height is the actual pixel buffer
resolution, the width/height in NativeHandleBuffer is the resolution we will
scale to. A generic external user should be unaware of the internal pixel buffer
size and only have to know what resolution NativeToI420Buffer() will have. So:
buffer_width >= crop_width >= width().

[tkchin_webrtc, 2016/10/19 22:50:17]

gotcha. Maybe short comment along those lines somewhere? (If this already exists
in a superclass that's fine too)

+  const int buffer_height_;
+  const int crop_width_;
+  const int crop_height_;
+  const int crop_x_;
+  const int crop_y_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_COMMON_VIDEO_INCLUDE_COREVIDEO_FRAME_BUFFER_H_