From 3e2e7038e6c2d338fbfebcb44cf9365cd1396d47 Mon Sep 17 00:00:00 2001
From: "marpan@webrtc.org"
 <marpan@webrtc.org@4adac7df-926f-26a2-2b94-8c16560cd09d>
Date: Mon, 16 Apr 2012 15:58:14 +0000
Subject: [PATCH] VPM: Allow for option to compute the content metrics every
 nth frame. Review URL: https://webrtc-codereview.appspot.com/492006

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2034 4adac7df-926f-26a2-2b94-8c16560cd09d
---
 .../main/source/frame_preprocessor.cc         | 19 +++++++++++++------
 .../main/source/frame_preprocessor.h          |  6 +++++-
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/src/modules/video_processing/main/source/frame_preprocessor.cc b/src/modules/video_processing/main/source/frame_preprocessor.cc
index 76fdac8384..c317528abc 100644
--- a/src/modules/video_processing/main/source/frame_preprocessor.cc
+++ b/src/modules/video_processing/main/source/frame_preprocessor.cc
@@ -18,7 +18,8 @@ _id(0),
 _contentMetrics(NULL),
 _maxFrameRate(0),
 _resampledFrame(),
-_enableCA(false)
+_enableCA(false),
+_frameCnt(0)
 {
     _spatialResampler = new VPMSimpleSpatialResampler();
     _ca = new VPMContentAnalysis(true);
@@ -49,6 +50,7 @@ VPMFramePreprocessor::Reset()
     _contentMetrics = NULL;
     _spatialResampler->Reset();
     _enableCA = false;
+    _frameCnt = 0;
 }
 	
     
@@ -160,14 +162,19 @@ VPMFramePreprocessor::PreprocessFrame(const VideoFrame* frame, VideoFrame** proc
       *processedFrame = &_resampledFrame;
     }
 
-    // Perform content analysis on the frame to be encoded
+    // Perform content analysis on the frame to be encoded.
     if (_enableCA)
     {
-        if (*processedFrame == NULL)  {
-          _contentMetrics = _ca->ComputeContentMetrics(frame);
-        } else {
-          _contentMetrics = _ca->ComputeContentMetrics(&_resampledFrame);
+        // Compute new metrics every |kSkipFramesCA| frames, starting with
+        // the first frame.
+        if (_frameCnt % kSkipFrameCA == 0) {
+          if (*processedFrame == NULL)  {
+            _contentMetrics = _ca->ComputeContentMetrics(frame);
+          } else {
+            _contentMetrics = _ca->ComputeContentMetrics(&_resampledFrame);
+          }
         }
+        ++_frameCnt;
     }
     return VPM_OK;
 }
diff --git a/src/modules/video_processing/main/source/frame_preprocessor.h b/src/modules/video_processing/main/source/frame_preprocessor.h
index 3c07a47e54..2d89c4e7fd 100644
--- a/src/modules/video_processing/main/source/frame_preprocessor.h
+++ b/src/modules/video_processing/main/source/frame_preprocessor.h
@@ -63,15 +63,19 @@ public:
     VideoContentMetrics* ContentMetrics() const;
 
 private:
+    // The content does not change so much every frame, so to reduce complexity
+    // we can compute new content metrics every |kSkipFrameCA| frames.
+    enum { kSkipFrameCA = 2 };
 
     WebRtc_Word32              _id;
     VideoContentMetrics*      _contentMetrics;
     WebRtc_UWord32             _maxFrameRate;
-    VideoFrame           _resampledFrame;
+    VideoFrame                _resampledFrame;
     VPMSpatialResampler*     _spatialResampler;
     VPMContentAnalysis*      _ca;
     VPMVideoDecimator*       _vd;
     bool                     _enableCA;
+    int                      _frameCnt;
     
 }; // end of VPMFramePreprocessor class definition