Add RTCFileVideoCapturer class.

webrtc/sdk/objc/Framework/Classes/PeerConnection/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;
+  AVAssetReaderTrackOutput *_outTrack;
+  BOOL _capturerStopped;
+  CMTime _lastPresentationTime;
+  dispatch_queue_t _frameQueue;
+}
+
+- (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 another file. Start capture request failed.");
+      return;
+    }
+    NSString *pathForFile = [self pathForFileName:nameOfFile];
+    if (!pathForFile) {
+      RTCLog("File %@ not found in bundle", nameOfFile);
+      return;
+    }
+
+    _lastPresentationTime = CMTimeMake(0, 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_420YpCbCr8BiPlanarFullRange)
+    };
+    _outTrack = [[AVAssetReaderTrackOutput alloc] initWithTrack:allTracks.firstObject
+                                                 outputSettings:options];
+    [_reader addOutput:_outTrack];
+
+    [_reader startReading];
+    RTCLog(@"File capturer started reading");
+    [self readNextBuffer];
+  });
+}
+
+- (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)readNextBuffer {
+  if (_reader.status != AVAssetReaderStatusReading || _capturerStopped) {
+    [_reader cancelReading];
+    _reader = nil;
+    return;
+  }
+
+  CMSampleBufferRef sampleBuffer = [_outTrack copyNextSampleBuffer];
+  if (!sampleBuffer) {
+    [self readNextBuffer];
+    return;
+  }
+  if (CMSampleBufferGetNumSamples(sampleBuffer) != 1 || !CMSampleBufferIsValid(sampleBuffer) ||
+      !CMSampleBufferDataIsReady(sampleBuffer)) {
+    [self readNextBuffer];
+    return;
+  }
+
+  [self publishSampleBuffer:sampleBuffer];
+}
+
+- (void)publishSampleBuffer:(CMSampleBufferRef)sampleBuffer {
+  CMTime presentationTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
+  Float64 presentationDifference =
+      CMTimeGetSeconds(CMTimeSubtract(presentationTime, _lastPresentationTime));
+  _lastPresentationTime = presentationTime;
+  int64_t presentationDifferenceRound = lroundf(presentationDifference * NSEC_PER_SEC);
+
+  __block dispatch_source_t timer = [self createStrictTimer];
+  // Strict timer that will fire |presentationDifferenceRound| ns from now and never again.
+  dispatch_source_set_timer(timer,
+                            dispatch_time(DISPATCH_TIME_NOW, presentationDifferenceRound),
+                            DISPATCH_TIME_FOREVER,
+                            0);
+  dispatch_source_set_event_handler(timer, ^{
+    dispatch_source_cancel(timer);
+    timer = nil;
+
+    CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
+    if (!pixelBuffer) {
+      CFRelease(sampleBuffer);
+      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+        [self readNextBuffer];
+      });
+      return;
+    }
+
+    NSTimeInterval timeStampSeconds = CACurrentMediaTime();
+    int64_t timeStampNs = lroundf(timeStampSeconds * NSEC_PER_SEC);
+    RTCVideoFrame *videoFrame =
+        [[RTCVideoFrame alloc] initWithPixelBuffer:pixelBuffer rotation:0 timeStampNs:timeStampNs];
+    CFRelease(sampleBuffer);
+
+    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+      [self readNextBuffer];
+    });
+
+    [self.delegate capturer:self didCaptureVideoFrame:videoFrame];
+  });
+  dispatch_activate(timer);
+}
+
+- (dispatch_source_t)createStrictTimer {
+  dispatch_source_t timer = dispatch_source_create(
+      DISPATCH_SOURCE_TYPE_TIMER, 0, DISPATCH_TIMER_STRICT, [self frameQueue]);
+  return timer;
+}
+
+- (void)dealloc {
+  [self stopCapture];
+}
+
+@end