Handle iOS devices with no rear-facing camera

talk/app/webrtc/objc/avfoundationvideocapturer.mm

 /*
  * libjingle
  * Copyright 2015 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 35 matching lines @@
 // This class used to capture frames using AVFoundation APIs on iOS. It is meant
 // to be owned by an instance of AVFoundationVideoCapturer. The reason for this
 // because other webrtc objects own cricket::VideoCapturer, which is not
 // ref counted. To prevent bad behavior we do not expose this class directly.
 @interface RTCAVFoundationVideoCapturerInternal : NSObject
     <AVCaptureVideoDataOutputSampleBufferDelegate>
 
 @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
 // it.
 - (instancetype)initWithCapturer:(webrtc::AVFoundationVideoCapturer*)capturer;
 - (void)startCaptureAsync;
 - (void)stopCaptureAsync;
 
 @end
 
@@ skipping 32 matching lines @@
   }
   return self;
 }
 
 - (void)dealloc {
   [self stopCaptureAsync];
   [[NSNotificationCenter defaultCenter] removeObserver:self];
   _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];
 }
 
 - (void)startCaptureAsync {
   if (_isRunning) {
     return;
   }
   _orientationHasChanged = NO;
   [[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
@@ skipping 74 matching lines @@
   AVCaptureDevice* backCaptureDevice = nil;
   for (AVCaptureDevice* captureDevice in
        [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]) {
     if (captureDevice.position == AVCaptureDevicePositionBack) {
       backCaptureDevice = captureDevice;
     }
     if (captureDevice.position == AVCaptureDevicePositionFront) {
       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;
   _frontDeviceInput =
       [AVCaptureDeviceInput deviceInputWithDevice:frontCaptureDevice
                                             error:&error];
   if (!_frontDeviceInput) {
     NSLog(@"Failed to get capture device input: %@",
           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;
   }
   [self updateSessionInput];
 
   return YES;
 }
 
 - (void)deviceOrientationDidChange:(NSNotification*)notification {
   _orientationHasChanged = YES;
@@ skipping 103 matching lines @@
 }
 
 bool AVFoundationVideoCapturer::IsRunning() {
   return _capturer.isRunning;
 }
 
 AVCaptureSession* AVFoundationVideoCapturer::GetCaptureSession() {
   return _capturer.captureSession;
 }
 
+bool AVFoundationVideoCapturer::CanUseBackCamera() const {
+  return _capturer.canUseBackCamera;
+}
+
 void AVFoundationVideoCapturer::SetUseBackCamera(bool useBackCamera) {
   _capturer.useBackCamera = useBackCamera;
 }
 
 bool AVFoundationVideoCapturer::GetUseBackCamera() const {
   return _capturer.useBackCamera;
 }
 
 void AVFoundationVideoCapturer::CaptureSampleBuffer(
     CMSampleBufferRef sampleBuffer) {
@@ skipping 62 matching lines @@
 
 void AVFoundationVideoCapturer::SignalFrameCapturedOnStartThread(
     const cricket::CapturedFrame* frame) {
   RTC_DCHECK(_startThread->IsCurrent());
   // This will call a superclass method that will perform the frame conversion
   // to I420.
   SignalFrameCaptured(this, frame);
 }
 
 }  // namespace webrtc