Qvideowidget displays nothing

Question

I’m trying to use the classes QMediaPlayer and QVideoWidget to display a video on a system I’m producing. Only these class rays don’t work as expected. The QVideoWidget just doesn’t show up, doesn’t show the video, doesn’t do anything!

THE MCVE

To illustrate the problem, I built a Minimum, Complete and Verifiable Example on the basis of in the Qt 5 documentation example itself. Below are the configuration files of Cmake (for setting up the environment - i.e., creating the Visual Studio or Makefile project) and code:

Cmakelists.txt:

cmake_minimum_required(VERSION 2.8.11)
project (Teste)

if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
  set(CMAKE_BUILD_TYPE Release CACHE STRING "Choose the type of build." FORCE)
  set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "Debug" "Release"
    "MinSizeRel" "RelWithDebInfo")
endif()

# Configuração do Qt
set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_AUTOUIC ON)
find_package(Qt5Widgets REQUIRED)
find_package(Qt5Multimedia REQUIRED)
find_package(Qt5MultimediaWidgets REQUIRED)

# Cria o executável
if(WIN32)
    add_executable(Teste WIN32 main.cpp)
else()
    add_executable(Teste main.cpp)
endif()

# Adiciona as bibliotecas necessárias
target_link_libraries(Teste Qt5::Widgets Qt5::Multimedia Qt5::MultimediaWidgets)

main.cpp:

#include <QApplication>
#include <QMediaPlayer>
#include <QVideoWidget>
#include <QMediaPlaylist>

int main(int argc, char** argv)
{
    QApplication app(argc, argv);

    QMediaPlayer *player;
    QMediaPlaylist *playlist;
    QVideoWidget *videoWidget;

    // Código tirado do exemplo em: http://doc.qt.io/qt-5/qvideowidget.html#details
    // -------------------------
    player = new QMediaPlayer;

    playlist = new QMediaPlaylist(player);
    playlist->addMedia(QUrl("http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_1mb.mp4"));
    playlist->addMedia(QUrl("http://techslides.com/demos/sample-videos/small.mp4"));

    videoWidget = new QVideoWidget;
    player->setVideoOutput(videoWidget);

    videoWidget->show();
    playlist->setCurrentIndex(1);
    player->play();
    // -------------------------

    return app.exec();
}

The Problem

When I run the code, the component (QVideoWidget) apparently not "is created" (despite being shown, since to ensure that the problem is not another I call show directly on the bastard), because the window appears "shortened" (without any standard size):

But even if I use the mouse to resize the window, there is nothing displayed:

The code does not generate any exceptions or errors. In the minimum example I use video Urls just to facilitate the tests (and as it is in the documentation), but on my local system I read local files and the problem is exactly the same.

The Environment

My development environment is:

• Windows 10 64 bits
• Cmake 3.5.0-rc3
• Qt 5.6.0 32 bits
• Visual Studio 2015

EDIT

I just tested on Ubuntu (16.04 64 bits) with Qt 5.7 (64 bits) and the problem is exactly the same:

Answer 1

I tested his example and he really doesn’t even try to run the file, when looking at the example he sent from the site it shows like this:

playlist = new QMediaPlaylist(player);

It seems to me that there are some errors in the documentation, the QMediaPlaylist you do not have the parameter to receive QMediaPlayer, but rather a QObject, that is to say it should only be to define the parent, has no relationship with creating the player, it seems an error of their tutorial, see how the class is QMediaPlaylist:

QMediaPlaylist(QObject *parent = 0);
virtual ~QMediaPlaylist();

Another thing I noticed when adding the "media items" you used QUrl, but I believe the right thing to do QMediaContent, for both remote and local files.

Another thing I noticed that it is necessary to set the minimum size of the QVideoWidget, otherwise he will render as 0, it is also possible to add it inside a QWidget or QMainWindow customized.

The @Luizviera also gave me a detail, the QUrl does not add the file:/// in local files, so it is necessary to use QUrl::fromLocalFile.

The code for basic operation would be like this:

QMediaContent videoItem1(QUrl::fromLocalFile("C:/Users/Guilherme/exemplo.mp4"));
playlist->addMedia(videoItem1);

I believe the right way is this:

player = new QMediaPlayer;

playlist = new QMediaPlaylist();

//Define o playlist no player
player->setPlaylist(playlist);

//item index 0
playlist->addMedia(QMediaContent(QUrl::fromLocalFile("http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_1mb.mp4")));

//item index 1
playlist->addMedia(QMediaContent(QUrl::fromLocalFile("http://techslides.com/demos/sample-videos/small.mp4")));

videoWidget = new QVideoWidget;
player->setVideoOutput(videoWidget);

videoWidget->show();

//Define o minimo do tamanho do video
videoWidget->setMinimumSize(100, 100);

playlist->setCurrentIndex(1);
player->play();

Only one note: a similar message appears in the Qt log (under Windows):

DirectShowPlayerService::doRender: Unresolved error code 80040266

It is due to lack of Codecs for x86/32bit version (as per your version)

One thing you can add is the events to check for other errors (change [SUA CLASSE] by the class where will organize the main, perhaps the custom window of a player):

• Your file .h usually:

  public slots:
      void statusChanged(QMediaPlayer::MediaStatus status);
      void displayErrorMessage();
  

• Your file .cpp usually:

  void [SUA CLASSE]::statusChanged(QMediaPlayer::MediaStatus status)
  {
      switch (status) {
      case QMediaPlayer::UnknownMediaStatus:
      case QMediaPlayer::NoMedia:
      case QMediaPlayer::LoadedMedia:
      case QMediaPlayer::BufferingMedia:
      case QMediaPlayer::BufferedMedia:
          qDebug() << status;
          break;
      case QMediaPlayer::LoadingMedia:
          qDebug() << "Loading...";
          break;
      case QMediaPlayer::StalledMedia:
          qDebug() << "Media Stalled";
          break;
      case QMediaPlayer::EndOfMedia:
          qDebug() << "Media end";
          break;
      case QMediaPlayer::InvalidMedia:
          displayErrorMessage();
          break;
      }
  }
  
  void [SUA CLASSE]::displayErrorMessage()
  {
      qDebug() << player->errorString();
  }
  

• And add the signals to the SLOTS:

  connect(player, SIGNAL(error(QMediaPlayer::Error)), this, SLOT(displayErrorMessage()));
  connect(player, SIGNAL(mediaStatusChanged(QMediaPlayer::MediaStatus)), this, SLOT(statusChanged(QMediaPlayer::MediaStatus)));
  

There is also a complete example to study in the documentation:

• http://doc.qt.io/qt-5/qtmultimedia-multimediawidgets-player-example.html

A test carried out:

video link: http://9gag.com/gag/adj442N/cat-exe-stops-working