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;

[sakal, 2017/05/19 11:53:16]

This seems to be accessed from multiple threads. Is it safe?

[daniela-webrtc, 2017/05/19 13:15:09]

This kind of usage with dispatch queues should be sage enough so no need to make
it atomic.

[sakal_google.com, 2017/05/19 13:20:04]

The main thing I am worried about is calling startCapturing immediately followed
by stopCapture. Is possible that the code setting the reader variable has not
been executed yet when stopCapture is called?

+  CMTime _lastPresentationTime;
+  dispatch_queue_t _frameQueue;
+  dispatch_semaphore_t _frameSemaphore;
+}
+
+- (void)startCapturingFromFileNamed:(NSString *)nameOfFile {
+  if (_reader && _reader.status == AVAssetReaderStatusReading) {
+    RTCLog("Capturer exists and reads anoter file. Start capture request failed.");

[kthelgason, 2017/05/19 12:18:47]

typo nit: reads another file.

+    return;
+  }
+
+  _lastPresentationTime = CMTimeMake(0, 0);
+  _frameSemaphore = dispatch_semaphore_create(0);
+
+  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+    NSString *pathForFile = [self pathForFileName:nameOfFile];
+    if (!pathForFile) {
+      RTCLog("File %@ not found in bundle", nameOfFile);
+      return;
+    }
+
+    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)
+    };
+    AVAssetReaderTrackOutput *outTrack =
+        [[AVAssetReaderTrackOutput alloc] initWithTrack:allTracks.firstObject
+                                         outputSettings:options];
+    [_reader addOutput:outTrack];
+
+    [_reader startReading];
+    while (_reader.status == AVAssetReaderStatusReading) {
+      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.
+        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);

[kthelgason, 2017/05/19 12:18:47]

no need to release the pixel buffer?

[daniela-webrtc, 2017/05/19 13:15:09]

No. The documentation for CMSampleBufferGetImageBuffer states 	
   @discussion The caller does not own the returned dataBuffer, and must retain
it explicitly if the caller needs to maintain a reference to it.

+
+              [self.delegate capturer:self didCaptureVideoFrame:videoFrame];
+              dispatch_semaphore_signal(_frameSemaphore);
+            });
+
+        dispatch_semaphore_wait(_frameSemaphore, DISPATCH_TIME_FOREVER);
+      }
+    }
+  });
+}
+
+- (void)stopCapture {
+  [_reader cancelReading];
+  _reader = nil;
+}
+
+#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)dealoc {

[sakal, 2017/05/19 11:53:16]

typo

+  [self stopCapture];
+}
+
+@end