Fix race condition in code for streaming segments to FFmpeg

This caused stuttering and jumps mostly in the beginning of a recording

common/src/main/java/ctbrec/recorder/download/hls/MergedFfmpegHlsDownload.java

@@ -13,6 +13,8 @@ import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.regex.Pattern;
 
 import org.slf4j.Logger;
@@ -40,6 +42,7 @@ public class MergedFfmpegHlsDownload extends AbstractHlsDownload {
     private transient Process ffmpegProcess;
     private transient OutputStream ffmpegStdIn;
     private transient BlockingQueue<Future<SegmentDownload>> queue = new LinkedBlockingQueue<>();
+    private transient Lock ffmpegStreamLock = new ReentrantLock();
 
     public MergedFfmpegHlsDownload(HttpClient client) {
         super(client);
@@ -78,30 +81,31 @@ public class MergedFfmpegHlsDownload extends AbstractHlsDownload {
     }
 
     private void streamSegmentDataToFfmpeg() {
-        while (!queue.isEmpty() && !Thread.currentThread().isInterrupted()) {
+        downloadExecutor.submit(() -> {
+            ffmpegStreamLock.lock();
             try {
-                Future<SegmentDownload> future = queue.peek();
-                if (running && future.isDone()) {
-                    queue.take();
-                    SegmentDownload segmentDownload = future.get();
-                    downloadExecutor.submit(() -> {
-                        ByteArrayOutputStream downloadData = (ByteArrayOutputStream) segmentDownload.getOutputStream();
-                        try {
-                            ffmpegStdIn.write(downloadData.toByteArray());
-                        } catch (IOException e) {
-                            LOG.error("Couldn't stream segment data to FFmpeg", e);
+                while (!queue.isEmpty() && !Thread.currentThread().isInterrupted()) {
+                    try {
+                        Future<SegmentDownload> future = queue.peek();
+                        if (running && future.isDone()) {
+                            queue.take();
+                            SegmentDownload segmentDownload = future.get();
+                            ByteArrayOutputStream downloadData = (ByteArrayOutputStream) segmentDownload.getOutputStream();
+                            downloadData.writeTo(ffmpegStdIn);
+                        } else {
+                            // first download in queue not finished, let's continue with other stuff
+                            break;
                         }
-                    });
-                } else {
-                    // first download in queue not finished, let's continue with other stuff
-                    break;
+                    } catch (InterruptedException e) {
+                        Thread.currentThread().interrupt();
+                    } catch (Exception e) {
+                        LOG.error("Segment download failed for model {}", model, e);
+                    }
                 }
-            } catch (InterruptedException e) {
-                Thread.currentThread().interrupt();
-            } catch (Exception e) {
-                LOG.error("Segment download failed for model {}", model, e);
+            } finally {
+                ffmpegStreamLock.unlock();
             }
-        }
+        });
     }
 
     @Override

common/src/main/java/ctbrec/recorder/download/hls/SegmentDownload.java

@@ -81,6 +81,7 @@ public class SegmentDownload implements Callable<SegmentDownload> {
                 out.write(b, 0, length);
                 BandwidthMeter.add(length);
             }
+            out.flush();
             return true;
         } else {
             throw new HttpException(response.code(), response.message());
@@ -96,4 +97,8 @@ public class SegmentDownload implements Callable<SegmentDownload> {
     public OutputStream getOutputStream() {
         return out;
     }
+
+    public URL getUrl() {
+        return url;
+    }
 }