QMediaPlayer doesn't recognize duration of mono-CBR of mp3, but mono VBR does.

[lisco]

subj, this happened in Linux, but on Windows duration is very well of any mp3.

some code of modified player example is here

connect(m_player, &QMediaPlayer::durationChanged, this, &Player::durationChanged);

fileDialog.setDirectory(QStandardPaths::standardLocations(QStandardPaths::MusicLocation).value(0, QDir::homePath()));
openFile(fileDialog.getOpenFileName());

void Player::openFile(const QString fileName)
{
	QFile file(fileName);
	if (!file.open(QIODevice::ReadOnly))
		return;
	m_data = file.readAll();

	m_buffer = new QBuffer(this);
	m_buffer->setData(m_data);
	m_buffer->open(QIODevice::ReadOnly);

	QMediaContent content;
	m_player->setMedia(QMediaContent(), m_buffer); 
}

void Player::durationChanged(qint64 duration)
{
	auto status = m_player->mediaStatus();
	if (status == QMediaPlayer::LoadedMedia || status == QMediaPlayer::LoadingMedia) {
		m_duration = duration / 1000;
		m_slider->setMaximum(m_duration);

		updateDurationInfo(m_duration);
	}
}

[lisco]

Windows uses directshow for duration, linux uses gstreamer, maybe something is wrong with it , the gst_element_query_duration method I try to debug.

[lisco]

durationChanged doesn't event at all on mono mp3 CBR.

[SGaist]

Hi,

Does GStreamer handle it properly ?
Which version of GStreamer is it ?
On a side note, since Qt 6.5, the default backend is ffmpeg. You might have better results with it.

[lisco]

@SGaist said in QMediaPlayer doesn't recognize duration of mono-CBR of mp3, but mono VBR does.:

Does GStreamer handle it properly ?

How to know?
ldd doesn't show any missing.

Version is such that was in Debian 10.
Qt5.15.2

[SGaist]

Try to read the file using the GStreamer CLI to see if it handles the file and if it provides some more information.

[lisco]

if (m_pipeline && qt_gst_element_query_duration(m_pipeline, GST_FORMAT_TIME, &gstDuration))

returns gstDuration=-1 on mono-cbr mp3

@SGaist Did you mean to run gst-launch with pipeline to mp3?

ffmpeg -i metronom.mp3 2>&1 | grep Duration
Duration: 00:01:11.45, start: 0.000000, bitrate: 128 kb/s

ffmpeg -i metronom-mono.mp3 2>&1 | grep Duration
Duration: 00:01:11.48, start: 0.000000, bitrate: 128 kb/s

ffmpeg -i metronom-mono-vbr.mp3 2>&1 | grep Duration
Duration: 00:01:11.47, start: 0.025057, bitrate: 39 kb/s

Where start of ffmpeg is zeroed these files gst_element_query_duration fails to get duration.

[JoeCFD]

@lisco use gst_discoverer_new to find duration of media files before pipeline starts.
qt_gst_element_query_duration is used after pipeline is started and may take some time. Therefore, the result can be wrong.

[lisco]

Before callling qt_gst_element_query_duration the application uses 50-100ms delay after buffer is filled by setMedia, but result fails, except stereo or mono vbr.

[JoeCFD]

@lisco It is not reliable to use qt_gst_element_query_duration. If your media file is short(for example a beep sound file), you will not be able to get duration. Try to use gst_discoverer_new.