Question

我已尝试使用更多AudioStreamBasicDescription来处理m4a文件格式。我仍然遇到一些问题。

请有人告诉我m4a文件格式的确切AudioStreamBasicDescription。

Answer 1

您可以使用ExtAudioFileGetProperty从现有的m4a音频文件中获取ASBD。

有关详情Click here。

Answer 2

您可以使用2种（至少）不同的方法获取文件的ASBD。您可以使用'ExtAudioFileGetProperty'或'AudioFileGetProperty'。

AudioFileGetProperty：

Imports Microsoft.VisualStudio.TestTools.UnitTesting
Imports System.Reflection

<TestClass()>
Public Class Application

    <TestMethod()>
    Public Sub TestEnums()
        Dim ass As Assembly = Assembly.Load("Elektro.Application")

        Dim types As IEnumerable(Of Type) =
            From t As Type In ass.GetTypes() Where t.IsEnum

        For Each t As Type In types
            EnumHasRepeatedValues(t)
        Next
    End Sub

    Public Sub EnumHasRepeatedValues(ByVal t As Type)
        Assert.AreEqual([Enum].GetValues(t).Length,
                        [Enum].GetNames(t).Length,
                        String.Format("Enum {0}.{1} has defined repeated values.", 
                                      t.Namespace, t.Name))
    End Sub

End Class

ExtAudioFileGetProperty：

NSString *soundFilePath = [[NSBundle mainBundle] pathForResource:@"sample" ofType:@"m4a"];
CFURLRef soundFileURL = (__bridge CFURLRef)[NSURL fileURLWithPath:soundFilePath];

if (soundFileURL != nil) {

    AudioFileID audioFile;
    OSStatus theError = noErr;

    theError = AudioFileOpenURL(soundFileURL,
                                kAudioFileReadPermission,
                                0,
                                &audioFile);
    if(theError != noErr) {
        printf("AudioFileOpenURL failed!");
        return;
    }

    AudioStreamBasicDescription asbd;
    UInt32 size = sizeof(asbd);
    theError = AudioFileGetProperty(audioFile, kAudioFilePropertyDataFormat, &size, &asbd);

    if(theError != noErr) {
        printf("kAudioFilePropertyDataFormat failed!");
        return;
    } else {
        printf("Sample Rate : %f\n", asbd.mSampleRate);
        /*
         Float64             mSampleRate;
         AudioFormatID       mFormatID;
         AudioFormatFlags    mFormatFlags;
         UInt32              mBytesPerPacket;
         UInt32              mFramesPerPacket;
         UInt32              mBytesPerFrame;
         UInt32              mChannelsPerFrame;
         UInt32              mBitsPerChannel;
         UInt32              mReserved;
         */
    }
}

什么是m4a文件格式的AudioStreamBasicDescription

2 个答案: