QAudioDecoder does not expose metadata (Linux, GStreamer)

[Hazzl]

Hi there,

current Qt (5.13.1) does not seem to make audio file (mp3 or ogg) metadata available on Linux with gstreamer backend. I manage to decode the audio data just fine. However the MetadataAvailabe signal never fires. Also calling decoder->isMetaDataAvailable() always returns false. Is this expected behaviour? If so, how do I access metadata on this platform?

Thanks
Felix

[Pablo J. Rogina]

@Hazzl said in QAudioDecoder does not expose metadata (Linux, GStreamer):

audio file (mp3 or ogg) metadata available on Linux

just in case, are you positive the audio file you're working with has actual metadata?

[Hazzl]

@Pablo-J-Rogina yes, the files have associated tags. Those are also the things that interest me. However, wouldn't other metadata like bitrate or duration show up in any case of a supported encoding without there being any tags?

[Hazzl]

This is the code I'm working with:

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QTextStream out(stdout, QIODevice::WriteOnly);
    QAudioDecoder player;
    QAudioFormat format;

    format.setChannelCount(2);
    format.setSampleSize(16);
    format.setSampleRate(48000);
    format.setCodec("audio/pcm");
    format.setSampleType(QAudioFormat::SignedInt);
    player.setSourceFilename(a.arguments().at(1));    
    player.setAudioFormat(format);
    player.connect(&player, &QAudioDecoder::finished, &a, &QCoreApplication::quit);
    player.connect(&player, &QAudioDecoder::bufferReady, [&]
    {
        player.read();
    });
    player.connect(&player, &QMediaObject::metaDataAvailableChanged, [&]
    {
        if (player.isMetaDataAvailable())
        {
            for (QString key: player.availableMetaData())
                out << key << " = " << player.metaData(key).toString() << endl;
            a.quit();
        }
    });
    player.start();

    return a.exec();
}

This goes through the entire file and discards the decoded data. However I never get any metadata out. Curiously enough, if I replace QAudioDecoder with a QMediaPlayer then everything works as expected. Can anybody point out where I go wrong with my QAudioDecoder?

[SGaist]

Hi,

I haven't take a look at the code of the class but from the documentation description I would say that its goal is to play efficiently local files without all the bells and whistles provided by QMediaPlayer.