这里我有一个代码，用于将音频文件覆盖为wav格式，以获得更好的质量并减小文件大小。这里我使用的是naudio文件压缩源代码，当我尝试转换该文件时遇到了一个异常。
必须已经是浮点
public string ConvertToWAV(string tempFilePath, string tempFileName, string audioType)
{
//Try to transform the file, if it fails use the original file
FileInfo fileInfo = new FileInfo(tempFilePath + tempFileName);
byte[] fileData = new byte[fileInfo.Length];
fileData = File.ReadAllBytes(tempFilePath + tempFileName);
ISampleProvider sampleProvider;
try
{
if (audioType.ToLower().Contains("wav"))
{
try
{
using (MemoryStream wav = new MemoryStream(fileData))
{
WaveStream stream = new WaveFileReader(wav);
WaveFormat target = new WaveFormat();
var s = new RawSourceWaveStream(new MemoryStream(), new WaveFormat(8000, 16, 1));
var c = new WaveFormatConversionStream(WaveFormat.CreateALawFormat(8000, 1), s);
sampleProvider = new WaveToSampleProvider(c);
WaveFileWriter.CreateWaveFile16(tempFilePath + tempFileName, sampleProvider);
wav.Close();
}
}
catch (Exception ex)
{
//We couldn't convert the file, continue with the original file.
}
}
}
catch (Exception ex)
{
throw ex;
}
return Convert.ToBase64String(fileData);
}
代码和概念通常存在一些问题。
首先，您将忽略输入文件的WaveFormat。我猜你假设它是8K，16位，1通道，基于你创建var s的线路，但这并不能保证。
其次，您不需要MemoryStream或RawSourceWaveStream。WaveFileReader是WaveStream，适用于任何"下一阶段"的NAudio波处理器。
第三（这很可能是你的例外）：NAudio Wave处理器和转换器不喜欢WaveFormat中的A-Law（或u-Law）。A-Law（和u-Law）在技术上不是PCM数据。因此，它们不是NAudio喜欢玩的"波浪"数据。
好的，说到这里，这里有一些建议。在NAudio.Codecs名称空间中有非常特殊的A-Law和u-Law编码器。奇怪的是，它们被命名为ALawEncoder和MuLawEncoder。这些东西是不兼容流，所以我们想让它们兼容。
我在末尾添加了一个类，它就是这样做的：创建一个IWaveProvider，它实际上吐出一个流a-Law或u-Law。下面是使用新类的测试代码。测试代码执行以下操作：
- 使用
MediaFoundationReader读取输入文件（我喜欢这个） - 使用
MediaFoundationResampler将输入格式转换为16位PCM（同时保持通道计数）。请注意，这意味着您的输入文件不必具有与A定律输出相同的格式，因此它几乎可以转换任何内容 - 将新的16位PCM流馈送到自定义的"ALaw到IWaveProvider"转换器类
- 将兼容
IWaveProvider的A-Law输出写入波形文件
我在这里使用MediaFoundation类，因为它们似乎不像基于ACM的类那样对波形格式特别。
static void ConversionTest( string _outfilename, string _infilename )
{
try
{
using( var reader = new MediaFoundationReader(_infilename) )
{
// Create a wave format for 16-bit pcm at 8000 samples per second.
int channels = reader.WaveFormat.Channels;
int rate = 8000;
int rawsize = 2;
int blockalign = rawsize * channels; // this is the size of one sample.
int bytespersecond = rate * blockalign;
var midformat =
WaveFormat.CreateCustomFormat( WaveFormatEncoding.Pcm,
rate,
channels,
bytespersecond,
blockalign,
rawsize * 8 );
// And a conversion stream to turn input into 16-bit PCM.
var midstream = new MediaFoundationResampler(reader, midformat);
//var midstream = new WaveFormatConversionStream(midformat, reader);
// The output stream is our custom stream.
var outstream = new PcmToALawConversionStream(midstream);
WaveFileWriter.CreateWaveFile(_outfilename, outstream);
}
}
catch( Exception _ex )
{
}
}
这是一个将16位PCM转换为A-Law或u-Law的类。最后是A-Law或u-Law的专业：
/// <summary>
/// Encodes 16-bit PCM input into A- or u-Law, presenting the output
/// as an IWaveProvider.
/// </summary>
public class PcmToG711ConversionStream : IWaveProvider
{
/// <summary>Gets the local a-law or u-law format.</summary>
public WaveFormat WaveFormat { get { return waveFormat; } }
/// <summary>Returns <paramref name="count"/> encoded bytes.</summary>
/// <remarks>
/// Note that <paramref name="count"/> is raw bytes. It doesn't consider
/// channel counts, etc.
/// </remarks>
/// <param name="buffer">The output buffer.</param>
/// <param name="offset">The starting position in the output buffer.</param>
/// <param name="count">The number of bytes to read.</param>
/// <returns>The total number of bytes encoded into <paramref name="buffer"/>.</returns>
public int Read(byte[] buffer, int offset, int count)
{
// We'll need a source buffer, twice the size of 'count'.
int shortcount = count*2;
byte [] rawsource = new byte [shortcount];
int sourcecount = Provider.Read(rawsource, 0, shortcount);
int bytecount = sourcecount / 2;
for( int index = 0; index < bytecount; ++index )
{
short source = BitConverter.ToInt16(rawsource, index*2);
buffer[offset+index] = Encode(source);
}
return bytecount;
}
/// <summary>
/// Initializes and A-Law or u-Law "WaveStream". The source stream
/// must be 16-bit PCM!
/// </summary>
/// <param name="_encoding">ALaw or MuLaw only.</param>
/// <param name="_sourcestream">The input PCM stream.</param>
public PcmToG711ConversionStream( WaveFormatEncoding _encoding,
IWaveProvider _provider )
{
Provider = _provider;
WaveFormat sourceformat = Provider.WaveFormat;
if( (sourceformat.Encoding != WaveFormatEncoding.Pcm) &&
(sourceformat.BitsPerSample != 16) )
{
throw new NotSupportedException("Input must be 16-bit PCM. Try using a conversion stream.");
}
if( _encoding == WaveFormatEncoding.ALaw )
{
Encode = this.EncodeALaw;
waveFormat = WaveFormat.CreateALawFormat( _provider.WaveFormat.SampleRate,
_provider.WaveFormat.Channels) ;
}
else if( _encoding == WaveFormatEncoding.MuLaw )
{
Encode = this.EncodeMuLaw;
waveFormat = WaveFormat.CreateMuLawFormat( _provider.WaveFormat.SampleRate,
_provider.WaveFormat.Channels) ;
}
else
{
throw new NotSupportedException("Encoding must be A-Law or u-Law");
}
}
/// <summary>The a-law or u-law encoder delegate.</summary>
EncodeHandler Encode;
/// <summary>a-law or u-law wave format.</summary>
WaveFormat waveFormat;
/// <summary>The input stream.</summary>
IWaveProvider Provider;
/// <summary>A-Law or u-Law encoder delegate.</summary>
/// <param name="_sample">The 16-bit PCM sample to encode.</param>
/// <returns>The encoded value.</returns>
delegate byte EncodeHandler( short _sample );
byte EncodeALaw( short _sample )
{
return ALawEncoder.LinearToALawSample(_sample);
}
byte EncodeMuLaw( short _sample )
{
return MuLawEncoder.LinearToMuLawSample(_sample);
}
}
public class PcmToALawConversionStream : PcmToG711ConversionStream
{
public PcmToALawConversionStream( IWaveProvider _provider )
: base(WaveFormatEncoding.ALaw, _provider)
{
}
}
public class PcmToMuLawConversionStream : PcmToG711ConversionStream
{
public PcmToMuLawConversionStream( IWaveProvider _provider )
: base(WaveFormatEncoding.MuLaw, _provider)
{
}
}
}
我终于找到了这个问题的解决方案，即需要添加一种名为Media Foundation的附加功能，以便在Windows Server 2012中更好地工作。
使用服务器管理器中的"添加角色和功能"向导。跳到Features并选择Media Foundation