iOS: Optimize video scaling and cropping

webrtc/common_video/libyuv/include/webrtc_libyuv.h

 /*
  *  Copyright (c) 2012 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.
  */
 
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 // Returns the PSNR in decibel, to a maximum of kInfinitePSNR.
 double I420PSNR(const VideoFrame* ref_frame, const VideoFrame* test_frame);
 double I420PSNR(const VideoFrameBuffer& ref_buffer,
                 const VideoFrameBuffer& test_buffer);
 
 // Compute SSIM for an I420 frame (all planes).
 double I420SSIM(const VideoFrame* ref_frame, const VideoFrame* test_frame);
 double I420SSIM(const VideoFrameBuffer& ref_buffer,
                 const VideoFrameBuffer& test_buffer);
 
+// Helper function for scaling NV12 to NV12.
+void NV12Scale(std::vector<uint8_t>* tmp_buffer,
+               const uint8_t* src_y, int src_stride_y,
+               const uint8_t* src_uv, int src_stride_uv,
+               int src_width, int src_height,
+               uint8_t* dst_y, int dst_stride_y,
+               uint8_t* dst_uv, int dst_stride_uv,
+               int dst_width, int dst_height);
+
 // Helper class for directly converting and scaling NV12 to I420. The Y-plane
 // will be scaled directly to the I420 destination, which makes this faster
 // than separate NV12->I420 + I420->I420 scaling.
 class NV12ToI420Scaler {
  public:
   void NV12ToI420Scale(const uint8_t* src_y, int src_stride_y,
                        const uint8_t* src_uv, int src_stride_uv,
                        int src_width, int src_height,
                        uint8_t* dst_y, int dst_stride_y,
                        uint8_t* dst_u, int dst_stride_u,
                        uint8_t* dst_v, int dst_stride_v,
                        int dst_width, int dst_height);
  private:
   std::vector<uint8_t> tmp_uv_planes_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_COMMON_VIDEO_LIBYUV_INCLUDE_WEBRTC_LIBYUV_H_