static AudioStreamBasicDescription GetOutputDescription(AudioStreamBasicDescription inputDescription)
{
var result = new AudioStreamBasicDescription
{
SampleRate = inputDescription.SampleRate,
FramesPerPacket = 4096,
AudioFormat = AudioFormat.AppleLossless,
ChannelsPerFrame = inputDescription.ChannelsPerFrame
};
switch (inputDescription.BitsPerChannel)
{
case 16:
result.Flags = AudioFormatFlags.Alac16BitSourceData;
break;
case 20:
result.Flags = AudioFormatFlags.Alac20BitSourceData;
break;
case 24:
result.Flags = AudioFormatFlags.Alac24BitSourceData;
break;
case 32:
result.Flags = AudioFormatFlags.Alac32BitSourceData;
break;
default:
throw new AudioUnsupportedException(
$"ALAC does not support {inputDescription.BitsPerChannel}-bit audio.");
}
return(result);
}
public ExtendedAudioFile(
AudioStreamBasicDescription description,
AudioFileType fileType,
[NotNull] Stream stream)
: base(description, fileType, stream)
{
SafeNativeMethods.ExtAudioFileWrapAudioFile(Handle, true, out _handle);
}
internal static extern AudioFileStatus AudioFileInitializeWithCallbacks(
IntPtr userData,
[NotNull] NativeCallbacks.AudioFileReadCallback readCallback,
[NotNull] NativeCallbacks.AudioFileWriteCallback writeCallback,
[NotNull] NativeCallbacks.AudioFileGetSizeCallback getSizeCallback,
[NotNull] NativeCallbacks.AudioFileSetSizeCallback setSizeCallback,
AudioFileType fileType,
ref AudioStreamBasicDescription description,
uint flags,
[NotNull] out AudioFileHandle handle);
internal AudioConverter(ref AudioStreamBasicDescription inputDescription,
ref AudioStreamBasicDescription outputDescription,
[NotNull] AudioFile audioFile)
{
_inputCallback = InputCallback;
SafeNativeMethods.AudioConverterNew(ref inputDescription,
ref outputDescription, out _handle);
_audioFile = audioFile;
}
internal AudioFile(AudioStreamBasicDescription description, AudioFileType fileType, [NotNull] Stream stream)
{
// This constructor is for writing
_readCallback = ReadCallback;
_getSizeCallback = GetSizeCallback;
_writeCallback = WriteCallback;
_setSizeCallback = SetSizeCallback;
_stream = stream;
SafeNativeMethods.AudioFileInitializeWithCallbacks(IntPtr.Zero,
_readCallback, _writeCallback, _getSizeCallback, _setSizeCallback,
fileType, ref description, 0, out var handle);
Handle = handle;
}
public void Initialize(Stream stream)
{
_audioFile = new AudioFile(AudioFileType.M4A, stream);
var inputDescription = _audioFile.GetProperty <AudioStreamBasicDescription>(AudioFilePropertyId.DataFormat);
if (inputDescription.AudioFormat != AudioFormat.AppleLossless)
{
throw new AudioUnsupportedException("The stream is not in Apple Lossless format.");
}
_outputDescription = GetOutputDescription(inputDescription);
_converter = new AudioConverter(ref inputDescription, ref _outputDescription, _audioFile);
_magicCookie = GetMagicCookie(_audioFile, _converter);
}
static AudioStreamBasicDescription GetOutputDescription(AudioStreamBasicDescription inputDescription)
{
var result = new AudioStreamBasicDescription
{
SampleRate = inputDescription.SampleRate,
FramesPerPacket = 1024,
AudioFormat = AudioFormat.AacLowComplexity,
ChannelsPerFrame = inputDescription.ChannelsPerFrame
};
switch (inputDescription.SampleRate)
{
case 192000:
case 144000:
case 128000: // conversion required
case 96000:
case 64000: // conversion required
case 48000:
result.SampleRate = 48000;
break;
case 176400:
case 88200:
case 44100:
case 37800: // conversion required
case 36000: // conversion required
result.SampleRate = 44100;
break;
case 32000:
case 28000: // conversion required
result.SampleRate = 32000;
break;
case 22050:
case 18900: // conversion required
result.SampleRate = 22050;
break;
default:
throw new AudioUnsupportedException(
$"Apple AAC does not support a {inputDescription.SampleRate} Hz sample rate.");
}
return(result);
}
static AudioStreamBasicDescription GetOutputDescription(AudioStreamBasicDescription inputDescription)
{
uint bitsPerSample;
// ReSharper disable once SwitchStatementMissingSomeCases
switch (inputDescription.Flags)
{
case AudioFormatFlags.Alac16BitSourceData:
bitsPerSample = 16;
break;
case AudioFormatFlags.Alac20BitSourceData:
bitsPerSample = 20;
break;
case AudioFormatFlags.Alac24BitSourceData:
bitsPerSample = 24;
break;
case AudioFormatFlags.Alac32BitSourceData:
bitsPerSample = 32;
break;
default:
throw new AudioUnsupportedException("Unknown audio format.");
}
return(new AudioStreamBasicDescription
{
AudioFormat = AudioFormat.LinearPcm,
Flags = AudioFormatFlags.PcmIsSignedInteger | AudioFormatFlags.PcmIsAlignedHigh,
BytesPerPacket = sizeof(int) * inputDescription.ChannelsPerFrame,
FramesPerPacket = 1,
BytesPerFrame = sizeof(int) * inputDescription.ChannelsPerFrame,
ChannelsPerFrame = inputDescription.ChannelsPerFrame,
BitsPerChannel = bitsPerSample,
SampleRate = inputDescription.SampleRate
});
}
static AudioStreamBasicDescription GetOutputDescription(AudioStreamBasicDescription inputDescription)
{
// ReSharper disable once SwitchExpressionHandlesSomeKnownEnumValuesWithExceptionInDefault
var bitsPerSample = inputDescription.Flags switch
{
AudioFormatFlags.Alac16BitSourceData => 16u,
AudioFormatFlags.Alac20BitSourceData => 20u,
AudioFormatFlags.Alac24BitSourceData => 24u,
AudioFormatFlags.Alac32BitSourceData => 32u,
_ => throw new AudioUnsupportedException("Unknown audio format.")
};
return(new()
{
AudioFormat = AudioFormat.LinearPcm,
Flags = AudioFormatFlags.PcmIsSignedInteger | AudioFormatFlags.PcmIsAlignedHigh,
BytesPerPacket = sizeof(int) * inputDescription.ChannelsPerFrame,
FramesPerPacket = 1,
BytesPerFrame = sizeof(int) * inputDescription.ChannelsPerFrame,
ChannelsPerFrame = inputDescription.ChannelsPerFrame,
BitsPerChannel = bitsPerSample,
SampleRate = inputDescription.SampleRate
});
}
internal static extern AudioConverterStatus AudioConverterNew(
ref AudioStreamBasicDescription sourceFormat,
ref AudioStreamBasicDescription destinationFormat,
[NotNull] out AudioConverterHandle handle);
public ExtendedAudioFile(
AudioStreamBasicDescription description,
AudioFileType fileType,
[NotNull] Stream stream)
: base(description, fileType, stream) =>
