View source for Seek in sound file

#REDIRECT [[Seek in Sound File]]

[[Category:Snippets]]
[[Category:HowTo]]

= How to Seek in Sound File =

I tried to play a sound file not at the beginning but with an offset of 20 seconds.

The following way of setting an offset '''fails''':
<code>player = new QMediaPlayer(this);
player->setMedia(QUrl::fromLocalFile("myCoolSong.mp3"));
player->setVolume(50);
player->play(); // music can be heard
qDebug() << player->isSeekable(); // is always false
player->setPosition ( 20*1000 ); //does not work</code>

'''''It does not work because QMediaPlayer works asynchronously.'''''

As soon as the seek operations are delayed everything works as intended. For example:

<code>CoolPlayer::on_Button1_clicked()
{
 qDebug() << player->isSeekable(); // true
 player->setPosition ( 20*1000 );
}</code>

To make my life easier I have derived a class MediaPlayer from QMediaPlayer and added a blocking load method:

<code>void MediaPlayer::loadBlocking(const QString &file;)
{
 setMedia(QUrl::fromLocalFile(file));
 if(!isSeekable())
 {
 QEventLoop loop;
 QTimer timer;
 timer.setSingleShot(true);
 timer.setInterval(2000);
 loop.connect(&timer;, SIGNAL (timeout()), &loop;, SLOT (quit()) );
 loop.connect(this, SIGNAL (seekableChanged(bool)), &loop;, SLOT (quit()));
 loop.exec();
 }
}</code>

When files are loaded with this blocking load method <code>setPosition()</code> can be called right in the next source line.
<code>loadBlocking</code> blocks until signal <code>seekableChanged()</code> is emitted. To avoid a deadlock, maximum waiting time is 2 seconds.