Libraries/DecoderWrapper/DecodedFrame.m

//
//  DecodedFrame.m
//  DecoderWrapper
//
//  Created by Mike Montalbo on 6/4/12.
//  Copyright (c) 2012 Dropcam. All rights reserved.
//

#import "DecodedFrame.h"
#import "NLCommonLoggingNVP.h"

static const CGFloat kDCSceneChangeThreshold = 100.0;
static const NSInteger kDCSubsampleRatio = 500;

@implementation DecodedFrame

+ (DecodedFrame *)decodedFrameWithWidth:(NSUInteger)width
                                 height:(NSUInteger)height
                            imageBuffer:(CVImageBufferRef)imageBuffer
                              timestamp:(int64_t)pts {
  return [[DecodedFrame alloc] initWithWidth:width
                                      height:height
                                 imageBuffer:imageBuffer
                                   timestamp:pts];
}

- (id)initWithWidth:(NSUInteger)width
             height:(NSUInteger)height
        yPlane:(NSData *)yPlane
        uPlane:(NSData *)uPlane
        vPlane:(NSData *)vPlane
     timestamp:(int64_t)pts {
  if((self = [super init])) {
    _width = width;
    _height = height;
    
    _yPlane = yPlane;
    _uPlane = uPlane;
    _vPlane = vPlane;
    _PTS = pts;
  }
  
  return self;
}

- (id)initWithWidth:(NSUInteger)width 
             height:(NSUInteger)height
        imageBuffer:(CVImageBufferRef)imageBuffer
          timestamp:(int64_t)pts {
  if((self = [super init])) {
    _width = width;
    _height = height;
    
    _imageBuffer = imageBuffer;
    CVBufferRetain(_imageBuffer);
    
    _PTS = pts;
  }
  
  return self;
}

- (NSData *)sceneChangeData {

  // only the Y'UV planes version of DecodedFrame is used, it seems.
  // we'll just use the luma (Y') plane.
  
  unsigned char *lumaBytes;
  size_t lumaLength;
  
  if (self.imageBuffer) {
    CVPixelBufferLockBaseAddress(self.imageBuffer, 0);
    lumaBytes = (unsigned char *)CVPixelBufferGetBaseAddress(self.imageBuffer);
    lumaLength = CVPixelBufferGetDataSize(self.imageBuffer);
  }
  else {
    lumaBytes = (unsigned char *)self.yPlane.bytes;
    lumaLength = self.yPlane.length;
  }

  NSMutableData *data = [NSMutableData dataWithLength:lumaLength / kDCSubsampleRatio];
  unsigned char *dataBytes = (unsigned char *)[data mutableBytes];

  float sum = 0;
  
  for(int i = 0; i < data.length; i++) {
    dataBytes[i] = lumaBytes[i * kDCSubsampleRatio];
    sum += dataBytes[i];
  }

  if (self.imageBuffer) {
    CVPixelBufferUnlockBaseAddress(self.imageBuffer, 0);
  }

  return [NSData dataWithData:data];
}

+ (BOOL)isSceneChangeFromData:(NSData *)data1 toData:(NSData *)data2 {  
  if((data1.length) != (data2.length))
    return NO;

  unsigned char *bytes1 = (unsigned char *)[data1 bytes];
  unsigned char *bytes2 = (unsigned char *)[data2 bytes];

  float diffSum = 0;
  
  for(int i = 0; i < data1.length; i++) {
    int diff = bytes1[i]-bytes2[i];
    diffSum += diff * diff;
  }
    
  BOOL isSceneChange = ((diffSum / data1.length) > kDCSceneChangeThreshold);
    
  if(isSceneChange)
    NLLogNVPInfo(@"scenechange detected, diff = %f", (diffSum / data1.length));
  
  return isSceneChange;
}

- (void)dealloc {
  CVBufferRelease(_imageBuffer);
}

@end