我怎么知道音频文件的格式？

Question

I want to make a music player and I want to filter out files not audio file on opening.
Should I use QAudioDecoder?
But every file I checked with QAudioDecoder tells me the same codec "audio/pcm".

QAudioDecoder decoder;
decoder.setSourceFilename(fileUrl.toLocalFile());
qDebug() << decoder.audioFormat().codec();

How do I know if the audio file's format is supported by Qt media player by not just checking if the file's name ends with ".mp3" or ".wav"?

And I found that some files' duration incorrect when playing on my music player. But when I play the file with other music player apps, it gives correct duration on other music players.

Or my app can't play some files but others can.
the console says :

DirectShowPlayerService::doSetUrlSource: Unresolved error code 0x80070002 (?t?Χ??????w?????C)

but after I change the file name, it can be opened.

How should I fix those on my music player instead of fixing the files' probably wrong or unsupported formats one by one?

---

I wrote this code to check if the file I opened is a supported audio file.

QMediaPlayer audioChecker;
audioChecker.setMedia(fileUrl);
qDebug() << audioChecker.media().canonicalUrl().fileName();
qDebug() << audioChecker.isAudioAvailable();
if(audioChecker.error() == QMediaPlayer::NoError) {
    qDebug() << "no error";
}
if(audioChecker.error() == QMediaPlayer::FormatError) {
    qDebug() << "format error";
}

and it tells me no error no matter what file I tested.

console:

"musicplayer.exe"
false
no error
"musicplayer.exe"
false
no error
"musicplayer.ilk"
false
no error
"musicplayer.exe"
false
no error
"a song.mp3"
false
no error

But how can files not audio file get no error? Why do audio file's audio not available?

---

Never mind. I just read that setMedia() return immediately and doesn't wait for the media to be loaded. so it's normal it gets no audio and no error because it's not loaded. I guess I'll make a thread class to check my file.

By the way, incorrect duration of the file is fixed somehow. Does it relate to LAV Splitter?

Answer 1

1. About how to check audio format in file without check its suffix, there's a tool names mediainfo , with the command line tool run as below:

    mediainfo -f [filepath] 

   You'll get the full information about the file, both video and audio if they exists. And among these parameters, there's a "format" value under "Audio" category, that indicates the actual audio format inside. eg. AAC/AC3

2. About the file can be played after name changed, I consider maybe there are some space characters in the filename, or the Player just can't access the file specified by name.

Answer 2

From Qt's documentation :

For playing media or audio files that are not simple, uncompressed audio, you can use the QMediaPlayer C++ class […] The compressed audio formats supported does depend on the operating system environment, and also what media plugins the user may have installed.

A simple example of how to use the QMediaPlayer class:

player = new QMediaPlayer;
// ...
player->setMedia(QUrl::fromLocalFile("/Users/me/Music/coolsong.mp3"));
player->setVolume(50);
player->play();

To verify that the codec is supported, you can use the error() method of the QMediaPlayer class which will return you an error code (see the documentation ).

So, after calling setMedia() , you can do something like:

if (player->error() == QMediaPlayer::FormatError)
{
    // Codec/format unsupported
}

---

About the error code you get when opening files:

• check that you have no \\ characters in your path (if you have some, escape them with another \\ )
• check if you have spaces, special characters, etc.