Add RTCFileVideoCapturer class.

webrtc/sdk/objc/Framework/Classes/RTCFileVideoCapturer.m

+/**
+ *  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 "RTCFileVideoCapturer.h"
+
+#import "WebRTC/RTCLogging.h"
+
+@implementation RTCFileVideoCapturer {
+  AVAssetReader *_reader;
+  CMTime _lastPresentationTime;
+  dispatch_queue_t _frameQueue;
+  dispatch_semaphore_t _frameSemaphore;
+  BOOL _capturerStopped;

[sakal, 2017/05/24 08:34:09]

I think this should be a property declared as atomic or marked as volatile.

[daniela-webrtc, 2017/06/01 13:08:57]

Not necessarily. The worst thing that can happen is that few frames slip by but
it's not worth paying the price of locking the variable.

+}
+
+- (void)startCapturingFromFileNamed:(NSString *)nameOfFile {
+  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+    if (_reader && _reader.status == AVAssetReaderStatusReading) {
+      RTCLog("Capturer exists and reads anoth6er file. Start capture request failed.");

[magjed_webrtc, 2017/05/29 13:14:25]

nit: anoth6er

[daniela-webrtc, 2017/06/01 13:08:57]

Done.

+      return;
+    }
+    NSString *pathForFile = [self pathForFileName:nameOfFile];
+    if (!pathForFile) {
+      RTCLog("File %@ not found in bundle", nameOfFile);
+      return;
+    }
+
+    _lastPresentationTime = CMTimeMake(0, 0);
+    _frameSemaphore = dispatch_semaphore_create(0);
+
+    NSURL *URLForFile = [NSURL fileURLWithPath:pathForFile];
+    AVURLAsset *asset = [AVURLAsset URLAssetWithURL:URLForFile options:nil];
+
+    NSArray *allTracks = [asset tracksWithMediaType:AVMediaTypeVideo];
+    NSError *error = nil;
+    _reader = [[AVAssetReader alloc] initWithAsset:asset error:&error];
+    if (error) {
+      RTCLog("File reader failed with error: %@", error);
+      return;
+    }
+
+    NSDictionary *options = @{
+      (NSString *)
+      kCVPixelBufferPixelFormatTypeKey : @(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange)

[magjed_webrtc, 2017/05/29 13:14:25]

Is it possible to use FullRange?

[daniela-webrtc, 2017/06/01 13:08:57]

Yes. I've changed it

+    };
+    AVAssetReaderTrackOutput *outTrack =
+        [[AVAssetReaderTrackOutput alloc] initWithTrack:allTracks.firstObject
+                                         outputSettings:options];
+    [_reader addOutput:outTrack];
+
+    [_reader startReading];
+    RTCLog(@"File capturer started reading");
+    while (_reader.status == AVAssetReaderStatusReading && !_capturerStopped) {
+      CMSampleBufferRef sampleBuffer = [outTrack copyNextSampleBuffer];
+      if (sampleBuffer) {
+        if (CMSampleBufferGetNumSamples(sampleBuffer) != 1 ||
+            !CMSampleBufferIsValid(sampleBuffer) || !CMSampleBufferDataIsReady(sampleBuffer)) {
+          continue;
+        }
+
+        CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
+        if (pixelBuffer == nil) {
+          continue;
+        }
+
+        CMTime presentationTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
+        Float64 presentationDifference =
+            CMTimeGetSeconds(CMTimeSubtract(presentationTime, _lastPresentationTime));
+        int64_t presentationDifferenceRound = lroundf(presentationDifference * NSEC_PER_SEC);
+        _lastPresentationTime = presentationTime;
+
+        // dispatch with delay, we want to achieve a real time play.

[magjed_webrtc, 2017/05/29 13:14:25]

nit: Begin sentence with capital letter.

+        dispatch_after(
+            dispatch_time(DISPATCH_TIME_NOW, presentationDifferenceRound), [self frameQueue], ^{
+              int64_t timeStampNs = CACurrentMediaTime() * NSEC_PER_SEC;
+              RTCVideoFrame *videoFrame = [[RTCVideoFrame alloc] initWithPixelBuffer:pixelBuffer
+                                                                            rotation:0
+                                                                         timeStampNs:timeStampNs];
+              CFRelease(sampleBuffer);
+
+              [self.delegate capturer:self didCaptureVideoFrame:videoFrame];
+              dispatch_semaphore_signal(_frameSemaphore);

[magjed_webrtc, 2017/05/29 13:14:25]

I would like to only use one frame queue and avoid blocking, as we discussed
offline.

[daniela-webrtc, 2017/06/01 13:08:57]

I've removed the semaphore and the blocking and now the buffers are posted to
the frame queue. However I still want to keep the frameQueue separate and
perform the rest of the tasks on separate queue. It's cleaner approach and is
inline with what other capturers (for instance the camera one) would do.

[magjed_webrtc, 2017/06/01 13:44:37]

Sure, we can have a separate frameQueue to publish frames on, as long as we
don't synchronize the queues by blocking.

+            });
+
+        dispatch_semaphore_wait(_frameSemaphore, DISPATCH_TIME_FOREVER);
+      }
+    }
+    [_reader cancelReading];
+    _reader = nil;
+  });
+}
+
+- (void)stopCapture {
+  _capturerStopped = YES;
+  RTCLog(@"File capturer stopped.");
+}
+
+#pragma mark - Private
+
+- (nullable NSString *)pathForFileName:(NSString *)fileName {
+  NSArray *nameComponents = [fileName componentsSeparatedByString:@"."];
+  if (nameComponents.count != 2) {
+    return nil;
+  }
+
+  NSString *path =
+      [[NSBundle mainBundle] pathForResource:nameComponents[0] ofType:nameComponents[1]];
+  return path;
+}
+
+- (dispatch_queue_t)frameQueue {
+  if (!_frameQueue) {
+    _frameQueue = dispatch_queue_create("org.webrtc.filecapturer.video", DISPATCH_QUEUE_SERIAL);
+    dispatch_set_target_queue(_frameQueue,
+                              dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0));
+  }
+  return _frameQueue;
+}
+
+- (void)dealloc {
+  [self stopCapture];
+}
+
+@end