Add stats overlay to iOS AppRTCDemo.

webrtc/examples/objc/AppRTCDemo/ARDBitrateTracker.m

Index: webrtc/examples/objc/AppRTCDemo/ARDBitrateTracker.m
diff --git a/webrtc/examples/objc/AppRTCDemo/ARDBitrateTracker.m b/webrtc/examples/objc/AppRTCDemo/ARDBitrateTracker.m
new file mode 100644
index 0000000000000000000000000000000000000000..8a20e6cc6d02b609fa6c4e84598fcc890087c86b
--- /dev/null
+++ b/webrtc/examples/objc/AppRTCDemo/ARDBitrateTracker.m
@@ -0,0 +1,51 @@
+/*
+ *  Copyright 2015 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.
+ */
+
+#import "ARDBitrateTracker.h"
+
+#import <QuartzCore/QuartzCore.h>
+
+@implementation ARDBitrateTracker {
+  CFTimeInterval _prevTime;
+  NSInteger _prevByteCount;
+}
+
+@synthesize bitrate = _bitrate;
+
++ (NSString *)bitrateStringForBitrate:(double)bitrate {
+  if (bitrate > 1e6) {
+    return [NSString stringWithFormat:@"%.2fMbps", bitrate * 1e-6];
+  } else if (bitrate > 1e3) {
+    return [NSString stringWithFormat:@"%.0fKbps", bitrate * 1e-3];
+  } else {
+    return [NSString stringWithFormat:@"%.0fbps", bitrate];
+  }
+}
+
+- (NSString *)bitrateString {
+  return [[self class] bitrateStringForBitrate:_bitrate];
+}
+
+- (void)updateBitrateWithCurrentByteCount:(NSInteger)byteCount {
+  CFTimeInterval currentTime = CACurrentMediaTime();
+  if (_prevTime) {
+    // For some reason we sometimes get byte counts that are not monotonic
+    // increasing. Those are ignored from calculations.
+    if (byteCount > _prevByteCount) {

[jiayl2, 2015/08/13 22:21:50]

I think we should update prev byte count and time in the else case too, e.g.
webrtc counter got reset after ICE restart. We don't want to be stuck in that
case.

The whole block can be simplified to:

if (_prevTime && byteCount > _prevByteCount) {
  _bitrate = ...
}
_prevByteCount = ...
_prevTime = ...

[tkchin_webrtc, 2015/08/13 23:55:31]

Done. Needed to add the active connection check. I was getting bad values
because of that.

+      _bitrate = (byteCount - _prevByteCount) * 8 / (currentTime - _prevTime);
+      _prevByteCount = byteCount;
+      _prevTime = currentTime;
+    }
+  } else {
+    _prevTime = currentTime;
+  }
+}
+
+@end