IFTTAnimation accumulates errors in a subtle way. Every time you add an animation, the timeline gets one extra entry. Here's my fix. Note that the inner for-loop used to break when j <= nextKeyFrameTime. Suppose you have keyFrames at times 100, 200, and 300. With <= nextKeyFrameTime, you'll get two entries for time 100, 200, and 300, and you'll …

gistfile1.txt

    self.timeline = [NSMutableArray new];
    for (NSUInteger i = 0; i < self.keyFrames.count - 1; i++) {
        IFTTTAnimationKeyFrame *keyFrame = [self.keyFrames objectAtIndex:i];
        IFTTTAnimationKeyFrame *nextKeyFrame = [self.keyFrames objectAtIndex:i+1];
        
        NSInteger j;
        for (j = keyFrame.time; j < nextKeyFrame.time; j++) {
            [self.timeline addObject:[self frameForTime:j startKeyFrame:keyFrame endKeyFrame:nextKeyFrame]];
        }
        if (i + 1 == self.keyFrames.count - 1) {
            [self.timeline addObject:[self frameForTime:j startKeyFrame:keyFrame endKeyFrame:nextKeyFrame]];
        }
    }
    
    self.startTime = ((IFTTTAnimationKeyFrame *)[self.keyFrames objectAtIndex:0]).time;