/// <summary>
/// 通过Url下载音频数据到内存流
/// </summary>
/// <param name="url"></param>
public Mp3NetworkStream(string url)
{
//需要将网络流全部读入内存中，因为网络流是不能直接查找的
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
WebResponse response = request.GetResponse();
using (Stream stream = response.GetResponseStream())
{
mp3Stream = new MemoryStream();
byte[] byteBuffer = new byte[1024];
if (stream != null)
{
int iReadSize = stream.Read(byteBuffer, 0, byteBuffer.Length);
while (iReadSize > 0)
{
mp3Stream.Write(byteBuffer, 0, iReadSize);
iReadSize = stream.Read(byteBuffer, 0, byteBuffer.Length);
}
stream.Close();
stream.Dispose();
}
mp3Stream.Flush();
mp3Stream.Position = 0;
id3v2Tag = Id3v2Tag.ReadTag(mp3Stream);
dataStartPosition = mp3Stream.Position;
var mp3Frame = Mp3Frame.LoadFromStream(mp3Stream);
sampleRate = mp3Frame.SampleRate;
frameLengthInBytes = mp3Frame.FrameLength;
double bitRate = mp3Frame.BitRate;
xingHeader = XingHeader.LoadXingHeader(mp3Frame);
// If the header exists, we can skip over it when decoding the rest of the file
if (xingHeader != null)
{
dataStartPosition = mp3Stream.Position;
}
mp3DataLength = mp3Stream.Length - dataStartPosition;
// try for an ID3v1 tag as well
mp3Stream.Position = mp3Stream.Length - 128;
byte[] tag = new byte[128];
mp3Stream.Read(tag, 0, 3);
if (tag[0] == 'T' && tag[1] == 'A' && tag[2] == 'G')
{
id3v1Tag = tag;
mp3DataLength -= 128;
}
mp3Stream.Position = dataStartPosition;
// create a temporary MP3 format before we know the real bitrate
Mp3WaveFormat = new Mp3WaveFormat(sampleRate, mp3Frame.ChannelMode == ChannelMode.Mono ? 1 : 2, frameLengthInBytes, (int)bitRate);
CreateTableOfContents();
tocIndex = 0;
// [Bit rate in Kilobits/sec] = [Length in kbits] / [time in seconds]
// = [Length in bits ] / [time in milliseconds]
// Note: in audio, 1 kilobit = 1000 bits.
bitRate = (mp3DataLength * 8.0 / TotalSeconds());
mp3Stream.Position = dataStartPosition;
// now we know the real bitrate we can create an accurate
Mp3WaveFormat = new Mp3WaveFormat(sampleRate, mp3Frame.ChannelMode == ChannelMode.Mono ? 1 : 2, frameLengthInBytes, (int)bitRate);
decompressor = CreateAcmFrameDecompressor(Mp3WaveFormat);
waveFormat = decompressor.OutputFormat;
bytesPerSample = (decompressor.OutputFormat.BitsPerSample) / 8 * decompressor.OutputFormat.Channels;
// no MP3 frames have more than 1152 samples in them
// some MP3s I seem to get double
decompressBuffer = new byte[1152 * bytesPerSample * 2];
}
response.Close();
}
/// <summary>
/// Load Xing Header
/// </summary>
/// <param name="frame">Frame</param>
/// <returns>Xing Header</returns>
public static XingHeader LoadXingHeader(Mp3Frame frame)
{
XingHeader xingHeader = new XingHeader();
xingHeader.frame = frame;
int offset;
if (frame.MpegVersion == MpegVersion.Version1)
{
if (frame.ChannelMode != ChannelMode.Mono)
{
offset = 32 + 4;
}
else
{
offset = 17 + 4;
}
}
else if (frame.MpegVersion == MpegVersion.Version2)
{
if (frame.ChannelMode != ChannelMode.Mono)
{
offset = 17 + 4;
}
else
{
offset = 9 + 4;
}
}
else
{
return(null);
// throw new FormatException("Unsupported MPEG Version");
}
if ((frame.RawData[offset + 0] == 'X') &&
(frame.RawData[offset + 1] == 'i') &&
(frame.RawData[offset + 2] == 'n') &&
(frame.RawData[offset + 3] == 'g'))
{
offset += 4;
}
else
{
return(null);
}
XingHeaderOptions flags = (XingHeaderOptions)ReadBigEndian(frame.RawData, offset);
offset += 4;
if ((flags & XingHeaderOptions.Frames) != 0)
{
xingHeader.framesOffset = offset;
offset += 4;
}
if ((flags & XingHeaderOptions.Bytes) != 0)
{
xingHeader.bytesOffset = offset;
offset += 4;
}
if ((flags & XingHeaderOptions.Toc) != 0)
{
offset += 100;
}
if ((flags & XingHeaderOptions.VbrScale) != 0)
{
xingHeader.vbrScale = ReadBigEndian(frame.RawData, offset);
}
return(xingHeader);
}
