add a realtimeStreaming example

CHANGELOG.md

@@ -1,4 +1,5 @@
 
+ * Add `FrameGrabber.grabAtFrameRate()` to simulate a device or stream when reading from files ([pull #1659](https://github.com/bytedeco/javacv/pull/1659))
  * Update `FFmpegFrameGrabber` and `FFmpegFrameRecorder` with new `avcodec` API ([issue #1498](https://github.com/bytedeco/javacv/issues/1498))
  * Add new `Similarity` sample with PSNR and MSSIM ([pull #1622](https://github.com/bytedeco/javacv/pull/1622))
  * Avoid crash in `FFmpegFrameRecorder.stop()` by moving `av_write_trailer()` out of `flush()` ([issue #1616](https://github.com/bytedeco/javacv/issues/1616))

platform/src/test/java/org/bytedeco/javacv/FrameGrabberTest.java

@@ -93,7 +93,8 @@ public void testFFmpegFrameGrabber() {
 
  int n = 0, m = 0;
  Frame frame2;
- while ((frame2 = grabber.grab()) != null) {
+ long startTime = System.nanoTime();
+ while ((frame2 = grabber.grabAtFrameRate()) != null) {
  Frame clone2 = frame2.clone();
  if (frame2.image != null) {
  Frame frame = frames[n++];
@@ -127,6 +128,8 @@ public void testFFmpegFrameGrabber() {
  }
  clone2.close();
  }
+ long stopTime = System.nanoTime();
+ assertEquals(n, (stopTime - startTime) * grabber.getFrameRate() / 1_000_000_000, 10.0);
  assertEquals(frames.length, n);
  assertEquals(null, grabber.grab());
  grabber.restart();

src/main/java/org/bytedeco/javacv/FrameGrabber.java

@@ -45,7 +45,7 @@
 public abstract class FrameGrabber implements Closeable {
 
  public static final List<String> list = new LinkedList<String>(Arrays.asList(new String[] {
- "DC1394", "FlyCapture", "FlyCapture2", "OpenKinect", "OpenKinect2", "RealSense", "RealSense2", "PS3Eye", "VideoInput", "OpenCV", "FFmpeg", "IPCamera" }));
+ "DC1394", "FlyCapture", "FlyCapture2", "OpenKinect", "OpenKinect2", "RealSense", "RealSense2", "PS3Eye", "VideoInput", "OpenCV", "FFmpeg", "IPCamera" }));
  public static void init() {
  for (String name : list) {
  try {
@@ -201,6 +201,7 @@ public static enum SampleMode {
  protected int frameNumber = 0;
  protected long timestamp = 0;
  protected int maxDelay = -1;
+ protected long startTime = 0;
 
  public int getVideoStream() {
  return videoStream;
@@ -724,4 +725,27 @@ public void release() throws Exception {
  public Array createArray(FrameGrabber[] frameGrabbers) {
  return new Array(frameGrabbers);
  }
+
+ /** Returns {@code frame = grab()} after {@code waitForTimestamp(frame)}. */
+ public Frame grabAtFrameRate() throws Exception, InterruptedException {
+ Frame frame = grab();
+ if (frame != null) {
+ waitForTimestamp(frame);
+ }
+ return frame;
+ }
+
+ /** Returns true if {@code Thread.sleep()} had to be called. */
+ public boolean waitForTimestamp(Frame frame) throws InterruptedException {
+ if (startTime == 0) {
+ startTime = System.nanoTime() / 1000 - frame.timestamp;
+ } else {
+ long delay = frame.timestamp - (System.nanoTime() / 1000 - startTime);
+ if (delay > 0) {
+ Thread.sleep(delay / 1000, (int)(delay % 1000) * 1000);
+ return true;
+ }
+ }
+ return false;
+ }
 }