Handle iOS devices with no rear-facing camera

talk/app/webrtc/objc/avfoundationvideocapturer.mm

Index: talk/app/webrtc/objc/avfoundationvideocapturer.mm
diff --git a/talk/app/webrtc/objc/avfoundationvideocapturer.mm b/talk/app/webrtc/objc/avfoundationvideocapturer.mm
index 0f9dc6825e9135461a6d8d8c5ad713c00c2c01b3..ed9f662910509d05c0b214780338b4ed9632b1ab 100644
--- a/talk/app/webrtc/objc/avfoundationvideocapturer.mm
+++ b/talk/app/webrtc/objc/avfoundationvideocapturer.mm
@@ -53,6 +53,7 @@ static cricket::VideoFormat const kDefaultFormat =
 @property(nonatomic, readonly) AVCaptureSession* captureSession;
 @property(nonatomic, readonly) BOOL isRunning;
 @property(nonatomic, assign) BOOL useBackCamera;  // Defaults to NO.
+@property(nonatomic, readonly) BOOL canUseBackCamera;

[tkchin_webrtc, 2016/03/14 18:16:59]

nit: move above useBackCamera

[hjon, 2016/03/14 18:31:44]

Done.

 
 // We keep a pointer back to AVFoundationVideoCapturer to make callbacks on it
 // when we receive frames. This is safe because this object should be owned by
@@ -105,10 +106,18 @@ static cricket::VideoFormat const kDefaultFormat =
   _capturer = nullptr;
 }
 
+- (BOOL)canUseBackCamera {
+  return _backDeviceInput != nil;
+}
+
 - (void)setUseBackCamera:(BOOL)useBackCamera {
   if (_useBackCamera == useBackCamera) {
     return;
   }
+  if (!self.canUseBackCamera) {
+    NSLog(@"No rear-facing camera exists or it cannot be used; not switching.");

[tkchin_webrtc, 2016/03/14 18:16:59]

import webrtc/base/RTCLogging and use RTCLog
here and elsewhere in file

[hjon, 2016/03/14 18:31:44]

Done.

+    return;
+  }
   _useBackCamera = useBackCamera;
   [self updateSessionInput];
 }
@@ -203,10 +212,15 @@ static cricket::VideoFormat const kDefaultFormat =
       frontCaptureDevice = captureDevice;
     }
   }
-  if (!frontCaptureDevice || !backCaptureDevice) {
-    NSLog(@"Failed to get capture devices.");
+  if (!frontCaptureDevice) {
+    NSLog(@"Failed to get front capture device.");
     return NO;
   }
+  if (!backCaptureDevice) {
+    NSLog(@"Failed to get back capture device");
+    // Don't return NO here because devices exist (16GB 5th generation iPod
+    // Touch) that don't have a rear-facing camera.
+  }
 
   // Set up the session inputs.
   NSError* error = nil;
@@ -218,18 +232,21 @@ static cricket::VideoFormat const kDefaultFormat =
           error.localizedDescription);
     return NO;
   }
-  _backDeviceInput =
-      [AVCaptureDeviceInput deviceInputWithDevice:backCaptureDevice
-                                            error:&error];
-  if (!_backDeviceInput) {
-    NSLog(@"Failed to get capture device input: %@",
-          error.localizedDescription);
-    return NO;
+  if (backCaptureDevice) {
+    _backDeviceInput =
+        [AVCaptureDeviceInput deviceInputWithDevice:backCaptureDevice
+                                              error:&error];
+    if (error) {
+      NSLog(@"Failed to get capture device input: %@",
+            error.localizedDescription);
+      _backDeviceInput = nil;
+      error = nil;

[tkchin_webrtc, 2016/03/14 18:16:59]

nil out error before _backDeviceInput = [AVCap.. instead. (So we keep around old
errors until we need to reuse the local var)

[hjon, 2016/03/14 18:31:44]

Done.

+    }
   }
 
   // Add the inputs.
   if (![_captureSession canAddInput:_frontDeviceInput] ||
-      ![_captureSession canAddInput:_backDeviceInput]) {
+      (_backDeviceInput && ![_captureSession canAddInput:_backDeviceInput])) {
     NSLog(@"Session does not support capture inputs.");
     return NO;
   }
@@ -353,6 +370,10 @@ AVCaptureSession* AVFoundationVideoCapturer::GetCaptureSession() {
   return _capturer.captureSession;
 }
 
+bool AVFoundationVideoCapturer::CanUseBackCamera() const {
+  return _capturer.canUseBackCamera;
+}
+
 void AVFoundationVideoCapturer::SetUseBackCamera(bool useBackCamera) {
   _capturer.useBackCamera = useBackCamera;
 }