Fixed video not playing after import

src/core/Source.cpp

@@ -27,6 +27,7 @@
 #include <QFileInfo>
 #include <QImageReader>
 #include <QSettings>
+#include <QTimer>
 
 namespace mmp {
 
@@ -206,6 +207,7 @@ void Image::_doPlay()
 /* Implementation of the Video class */
 Video::Video(int id) : Texture(id),
     _uri(""),
+    _videoType(VIDEO_URI),
     _impl(nullptr)
 {
   _impl = new VideoPlayerImpl();
@@ -354,17 +356,40 @@ bool Video::setUri(const QString &uri)
     // Set uri.
     _uri = uri;
 
-    // Try to get thumbnail.
-    // Wait for the first samples to be available to make sure we are ready.
-    if (!_impl->waitForNextBits(ICON_TIMEOUT))
+    // Show a generic icon right away. A real thumbnail (video files only) is
+    // filled in below, asynchronously, once frames actually start arriving:
+    // we cannot wait for it here without blocking the GUI thread, which is
+    // also the thread Qt Multimedia needs free to deliver those frames.
+    _setFallbackIcon();
+
+    const int maxAttempts = ICON_TIMEOUT / THUMBNAIL_POLL_INTERVAL;
+
+    if (_videoType == VIDEO_WEBCAM)
     {
-      qDebug() << "No bits coming" << Qt::endl;
-      return false;
+      // No thumbnail to generate for a camera: just confirm the feed comes up.
+      _pollForBits([this]() {
+        _emitPropertyChanged("icon");
+      }, maxAttempts);
     }
-
-    if (_videoType != VIDEO_WEBCAM) { // Generated thumbnail if source type is not camera
-      if (!_generateThumbnail())
-        qDebug() << "Could not generate thumbnail for " << uri << ": using generic icon." << Qt::endl;
+    else
+    {
+      _pollForBits([this, maxAttempts]() {
+        // Try seeking to the middle of the movie for a representative frame.
+        if (_impl->seekTo(0.5))
+        {
+          _pollForBits([this]() {
+            if (!_generateThumbnail())
+              qDebug() << "Could not generate thumbnail for " << _uri << ": using generic icon." << Qt::endl;
+            _impl->resetMovie();
+            _emitPropertyChanged("icon");
+          }, maxAttempts);
+        }
+        else
+        {
+          _impl->resetMovie();
+          _emitPropertyChanged("icon");
+        }
+      }, maxAttempts);
     }
 
     _emitPropertyChanged("uri");
@@ -386,37 +411,44 @@ void Video::_doPause()
   _impl->setPlayState(false);
 }
 
-bool Video::_generateThumbnail()
+void Video::_setFallbackIcon()
 {
   static QFileIconProvider provider;
 
-  // Default (in case seeking and loading don't work).
   _icon = provider.icon(QFileInfo(_uri));
-  if (_icon.isNull()) {
-    if (_uri.startsWith(QString("/dev/video"))) {
-      _icon = QIcon(":/add-camera");
-    }
-    else {
-      _icon = QIcon(":/add-video");
-    }
-  }
+  if (_icon.isNull())
+    _icon = (_videoType == VIDEO_WEBCAM) ? QIcon(":/add-camera") : QIcon(":/add-video");
+}
 
-  // Try seeking to the middle of the movie.
-  if (!_impl->seekTo(0.5))
+void Video::_pollForBits(std::function<void()> onReady, int attemptsLeft)
+{
+  if (_impl->hasBits() && _impl->bitsHaveChanged())
   {
-    _impl->resetMovie();
-    return false;
+    onReady();
+    return;
   }
 
-  // Try to get a sample from the current position.
-  // NOTE: There is no guarantee the sample has yet been acquired.
-  const uchar* bits;
-  if (!_impl->waitForNextBits(ICON_TIMEOUT, &bits))
+  if (attemptsLeft <= 0)
   {
-    qDebug() << "Second waiting wrong..." << Qt::endl;
-    return false;
+    qDebug() << "No bits coming for " << _uri << Qt::endl;
+    return;
   }
 
+  // Re-check shortly, giving the Qt event loop a chance to actually run and
+  // deliver the frame we're waiting for.
+  QTimer::singleShot(THUMBNAIL_POLL_INTERVAL, this, [this, onReady, attemptsLeft]() {
+    _pollForBits(onReady, attemptsLeft - 1);
+  });
+}
+
+bool Video::_generateThumbnail()
+{
+  // Assumes the caller (_pollForBits()'s onReady callback) has already
+  // confirmed a fresh frame is available.
+  const uchar* bits = _impl->getBits();
+  if (!bits)
+    return false;
+
   // Copy bits into thumbnail QImage.
   QImage thumbnail(getWidth(), getHeight(), QImage::Format_ARGB32);
   for (int y=0; y<getHeight(); y++)
@@ -434,9 +466,6 @@ bool Video::_generateThumbnail()
   _icon = QIcon(QPixmap::fromImage(thumbnail).scaled(MM::MAPPING_LIST_ICON_SIZE, MM::MAPPING_LIST_ICON_SIZE,
                                                      Qt::IgnoreAspectRatio));
 
-  // Reset movie.
-  _impl->resetMovie();
-
   return true;
 }
 

src/core/Source.h

@@ -24,6 +24,7 @@
 
 #include <QtGlobal>
 
+#include <functional>
 #include <string>
 #include <QColor>
 #include <QElapsedTimer>
@@ -332,6 +333,9 @@ class Video : public Texture
   // Thumbnail generation timeout (in ms).
   static const int ICON_TIMEOUT = 1000;
 
+  // How often to re-check for a decoded frame while polling (in ms).
+  static const int THUMBNAIL_POLL_INTERVAL = 50;
+
 public:
   Q_INVOKABLE Video(int id=NULL_UID);
   Video(const QString uri_, VideoType type, double rate, uid id=NULL_UID);
@@ -393,9 +397,25 @@ class Video : public Texture
   /// Pauses playback.
   virtual void _doPause();
 
-  // Try to generate a thumbnail from currently loaded movie.
+  // Sets a generic fallback icon (file icon, or a generic video/camera icon).
+  void _setFallbackIcon();
+
+  // Builds a thumbnail icon from the frame currently held by _impl. Assumes
+  // the caller has already confirmed a fresh frame is available (see
+  // _pollForBits()).
   bool _generateThumbnail();
 
+  // Polls (via the Qt event loop, never blocking) until _impl has a fresh
+  // frame, then calls onReady. Gives up silently after attemptsLeft tries.
+  //
+  // Qt Multimedia delivers frames asynchronously through the event loop of
+  // the thread that created the QMediaPlayer/QVideoSink (here, the GUI
+  // thread), so this cannot be replaced by a synchronous/blocking wait:
+  // blocking the GUI thread also blocks the delivery of the very frame being
+  // waited for, and starves the media backend's own event processing while
+  // doing so. See the removed VideoImpl::waitForNextBits().
+  void _pollForBits(std::function<void()> onReady, int attemptsLeft);
+
   QString _uri;
   QIcon _icon;
   VideoType _videoType;

src/core/VideoImpl.cpp

@@ -19,7 +19,6 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include "VideoImpl.h"
-#include <QElapsedTimer>
 #include <QSettings>
 #include <QDebug>
 
@@ -152,18 +151,4 @@ void VideoImpl::update()
 void VideoImpl::lockMutex()   { _mutex.lock(); }
 void VideoImpl::unlockMutex() { _mutex.unlock(); }
 
-bool VideoImpl::waitForNextBits(int timeout, const uchar** bits)
-{
-  QElapsedTimer timer;
-  timer.start();
-  while (timer.elapsed() < timeout) {
-    if (hasBits() && bitsHaveChanged()) {
-      if (bits)
-        *bits = getBits();
-      return true;
-    }
-  }
-  return false;
-}
-
 }

src/core/VideoImpl.h

@@ -108,9 +108,6 @@ class VideoImpl
   /// Unlocks mutex.
   void unlockMutex();
 
-  /// Blocks until new bits are available (up to timeout ms). Returns false on timeout.
-  bool waitForNextBits(int timeout, const uchar** bits = nullptr);
-
 protected:
   virtual void freeResources();
 

src/gui/MainWindow.cpp

@@ -370,6 +370,8 @@ void MainWindow::sourcePropertyChanged(uid id, QString propertyName, QVariant va
   QListWidgetItem* sourceItem = getItemFromId(*sourceList, id);
   if (propertyName == "name")
     sourceItem->setText(source->getName());
+  else if (propertyName == "icon")
+    sourceItem->setIcon(source->getIcon());
 }
 
 void MainWindow::closeEvent(QCloseEvent *event)