iOS video_capture: start camera in the background.

Camera start is a blocking operation so never a good idea to do on a main
thread, but worse than that is that the guts of WebView appear to be
interacting with capture start in a bad way causing startup to pause for 10s
while a timeout expires.  This change eliminates that 10s delay.

R=noahric@google.com

Review URL: https://webrtc-codereview.appspot.com/10449004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5772 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_capture/ios/rtc_video_capture_ios_objc.h

@@ -28,6 +28,8 @@
   AVCaptureSession* _captureSession;
   int _captureId;
   AVCaptureConnection* _connection;
+  BOOL _captureStarting;  // Guarded by _captureStartingCondition.
+  NSCondition* _captureStartingCondition;
 }
 
 @property webrtc::VideoCaptureRotation frameRotation;
@@ -37,7 +39,7 @@
 // default init methods have been overridden to return nil.
 - (id)initWithOwner:(webrtc::videocapturemodule::VideoCaptureIos*)owner
           captureId:(int)captureId;
-- (BOOL)setCaptureDeviceByUniqueId:(NSString*)uniequeId;
+- (BOOL)setCaptureDeviceByUniqueId:(NSString*)uniqueId;
 - (BOOL)startCaptureWithCapability:
         (const webrtc::VideoCaptureCapability&)capability;
 - (BOOL)stopCapture;

webrtc/modules/video_capture/ios/rtc_video_capture_ios_objc.mm

@@ -24,7 +24,6 @@ using namespace webrtc::videocapturemodule;
 
 @interface RTCVideoCaptureIosObjC (hidden)
 - (int)changeCaptureInputWithName:(NSString*)captureDeviceName;
-
 @end
 
 @implementation RTCVideoCaptureIosObjC
@@ -36,8 +35,10 @@ using namespace webrtc::videocapturemodule;
     _owner = owner;
     _captureId = captureId;
     _captureSession = [[AVCaptureSession alloc] init];
+    _captureStarting = NO;
+    _captureStartingCondition = [[NSCondition alloc] init];
 
-    if (!_captureSession) {
+    if (!_captureSession || !_captureStartingCondition) {
       return nil;
     }
 
@@ -144,6 +145,17 @@ using namespace webrtc::videocapturemodule;
     return NO;
   }
 
+  AVCaptureVideoDataOutput* currentOutput =
+      (AVCaptureVideoDataOutput*)[currentOutputs objectAtIndex:0];
+
+  dispatch_async(
+      dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
+      ^(void) { [self startCaptureInBackgroundWithOutput:currentOutput]; });
+  return YES;
+}
+
+- (void)startCaptureInBackgroundWithOutput:
+            (AVCaptureVideoDataOutput*)currentOutput {
   NSString* captureQuality =
       [NSString stringWithString:AVCaptureSessionPresetLow];
   if (_capability.width >= 1920 || _capability.height >= 1080) {
@@ -157,9 +169,6 @@ using namespace webrtc::videocapturemodule;
     captureQuality = [NSString stringWithString:AVCaptureSessionPreset352x288];
   }
 
-  AVCaptureVideoDataOutput* currentOutput =
-      (AVCaptureVideoDataOutput*)[currentOutputs objectAtIndex:0];
-
   // begin configuration for the AVCaptureSession
   [_captureSession beginConfiguration];
 
@@ -179,7 +188,10 @@ using namespace webrtc::videocapturemodule;
 
   [_captureSession startRunning];
 
-  return YES;
+  [_captureStartingCondition lock];
+  _captureStarting = NO;
+  [_captureStartingCondition signal];
+  [_captureStartingCondition unlock];
 }
 
 - (void)setRelativeVideoOrientation {
@@ -215,6 +227,7 @@ using namespace webrtc::videocapturemodule;
 }
 
 - (BOOL)stopCapture {
+  [self waitForCaptureStartToFinish];
   if (!_captureSession) {
     return NO;
   }
@@ -320,4 +333,11 @@ using namespace webrtc::videocapturemodule;
   CVPixelBufferUnlockBaseAddress(videoFrame, kFlags);
 }
 
+- (void)waitForCaptureStartToFinish {
+  [_captureStartingCondition lock];
+  while (_captureStarting) {
+    [_captureStartingCondition wait];
+  }
+  [_captureStartingCondition unlock];
+}
 @end