[iOS] Fix incorrectly oriented frames when rapidly switching between cameras.

webrtc/sdk/objc/Framework/Classes/Video/RTCImageHelper.mm

Index: webrtc/sdk/objc/Framework/Classes/Video/RTCImageHelper.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/Video/RTCImageHelper.mm b/webrtc/sdk/objc/Framework/Classes/Video/RTCImageHelper.mm
new file mode 100644
index 0000000000000000000000000000000000000000..8f348f11b7771b8c918896dece8ef757f291b6c0
--- /dev/null
+++ b/webrtc/sdk/objc/Framework/Classes/Video/RTCImageHelper.mm
@@ -0,0 +1,51 @@
+/*
+ *  Copyright 2017 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 "RTCImageHelper.h"

[tkchin_webrtc, 2017/07/24 21:30:37]

nit: blank line before #import

[jtt_webrtc, 2017/07/24 22:29:51]

Done.

+
+BOOL CFStringContainsString(CFStringRef theString, CFStringRef stringToFind) {
+  CFRange foundRange;

[tkchin_webrtc, 2017/07/24 21:30:37]

nit: always initialize vars
probably set length to zero, index to NSNotFound

[jtt_webrtc, 2017/07/24 22:29:51]

Since it's not used, I'll pass in nil.

+  return CFStringFindWithOptions(theString,
+                                 stringToFind,
+                                 CFRangeMake(0, CFStringGetLength(theString)),
+                                 kCFCompareCaseInsensitive,
+                                 &foundRange);
+}
+
+@implementation RTCImageHelper
+
++ (AVCaptureDevicePosition)cameraFromSampleBuffer:(CMSampleBufferRef)sampleBuffer {
+  // Check the image's EXIF for the actual camera the image came.
+  AVCaptureDevicePosition cameraPosition = AVCaptureDevicePositionUnspecified;
+  CFDictionaryRef attachments = CMCopyDictionaryOfAttachments(
+      kCFAllocatorDefault, sampleBuffer, kCMAttachmentMode_ShouldPropagate);
+  if (attachments) {
+    int size = CFDictionaryGetCount(attachments);
+    if (size > 0) {
+      CFDictionaryRef cfExifDictVal = NULL;

[tkchin_webrtc, 2017/07/24 21:30:37]

nit: nullptr

[jtt_webrtc, 2017/07/24 22:29:51]

Using nil as nullptr isn't defined here.

+      if (CFDictionaryGetValueIfPresent(
+              attachments, (const void *)CFSTR("{Exif}"), (const void **)&cfExifDictVal)) {

[tkchin_webrtc, 2017/07/24 21:30:37]

Consider declaring NSString * and toll bridge to CFString instead, or declaring
a static value somewhere

[tkchin_webrtc, 2017/07/24 21:30:37]

does the return val need to be released? what are the semantics for ownership
here?

[jtt_webrtc, 2017/07/24 22:29:51]

Retain count on the returned value is 1. So it is owned by the dictionary, hence
no need to release.

[jtt_webrtc, 2017/07/24 22:29:51]

CFSTR calls __builtin___CFStringMakeConstantString which adds it to an internal
dictionary and the string is reused, not created/released. So there is no need
to create a toll bridged NSString. See
https://opensource.apple.com/source/CF/CF-855.17/CFString.c

+        CFStringRef cfLensModelStrVal;
+        if (CFDictionaryGetValueIfPresent(cfExifDictVal,
+                                          (const void *)CFSTR("LensModel"),

[tkchin_webrtc, 2017/07/24 21:30:37]

similarly here

[jtt_webrtc, 2017/07/24 22:29:51]

See above.

+                                          (const void **)&cfLensModelStrVal)) {
+          if (CFStringContainsString(cfLensModelStrVal, CFSTR("front"))) {
+            cameraPosition = AVCaptureDevicePositionFront;
+          } else if (CFStringContainsString(cfLensModelStrVal, CFSTR("back"))) {
+            cameraPosition = AVCaptureDevicePositionBack;
+          }
+        }
+      }
+    }
+    CFRelease(attachments);
+  }
+  return cameraPosition;
+}
+
+@end