您需要在不同的线程中读取标题。
public class Mp3MediaStreamSource : MediaStreamSource
{
/// <summary>
/// ID3 version 1 tags are 128 bytes at the end of the file.
/// http://www.id3.org/ID3v1
/// </summary>
private const int Id3Version1TagSize = 128;
/// <summary>
/// Buffer for decoding audio frames into. 4096 should be larger than we'll ever need, right? (144*448*1000/44100)
/// </summary>
private static byte[] buffer = new byte[4096];
/// <summary>
/// The Mp3 stream being played back.
/// </summary>
private Stream audioStream;
/// <summary>
/// Description of the Mp3 Stream being played back which includes the
/// MpegLayer3WaveFormat structure serialized out as a string of hex
/// characters.
/// </summary>
private MediaStreamDescription audioStreamDescription;
/// <summary>
/// The position in the stream where the current MpegFrame starts.
/// For purposes of this code, the frame starts with the header and
/// not after the header.
/// </summary>
private long currentFrameStartPosition;
/// <summary>
/// The length of the audiostream as determined via the constructors.
/// </summary>
private long audioStreamLength;
/// <summary>
/// Holds the duration of the track
/// </summary>
private TimeSpan trackDuration;
/// <summary>
/// The current frame to parse
/// </summary>
private MpegFrame currentFrame;
private MpegFrame mpegLayer3Frame;
private bool readHeaderFail = false;
/// <summary>
/// Initializes a new instance of the Mp3MediaStreamSource class with a pre-determined length.
/// This is useful for wrapping an IO stream that may not be seekable (and thus won't have a .Length)
/// but for which you already know the length (e.g. a CryptoStream from an IsolatedStorageFileStream with a byte count,
/// or an HTTP stream which has a specified content-length)
/// </summary>
/// <param name="audioStream">Non-seekable Stream containing Mp3 data</param>
/// <param name="length">Length of non-seekable stream</param>
public Mp3MediaStreamSource(Stream audioStream, long length)
{
this.audioStream = audioStream;
this.audioStreamLength = length;
}
/// <summary>
/// Gets the MpegLayer3WaveFormat structure which represents this Mp3 file.
/// </summary>
public MpegLayer3WaveFormat MpegLayer3WaveFormat { get; private set; }
/// <summary>
/// Read off the Id3Data from the stream and return the first MpegFrame of the audio stream.
/// This assumes that the first bit of data is either an ID3 segment or an MPEG segment. Should
/// probably do something a bit more robust at some point.
/// </summary>
/// <returns>
/// The first MpegFrame in the audio stream.
/// </returns>
public MpegFrame ReadPastId3V2Tags()
{
/*
* Since this code assumes that the first bit of data is either an ID3 segment or an MPEG segment it could
* get into trouble. Should probably do something a bit more robust at some point.
*/
MpegFrame mpegFrame;
// Read and (throw out) any Id3 data if present.
byte[] data = new byte[10];
if (this.audioStream.Read(data, 0, 3) != 3)
{
goto cleanup;
}
if (data[0] == 73 /* I */ &&
data[1] == 68 /* D */ &&
data[2] == 51 /* 3 */)
{
// Need to update to read the is footer present flag and account for its 10 bytes if needed.
if (this.audioStream.Read(data, 3, 7) != 7)
{
goto cleanup;
}
int id3Size = BitTools.ConvertSyncSafeToInt32(data, 6);
int bytesRead = 0;
// Read through the ID3 Data tossing it out.
while (id3Size > 0)
{
bytesRead = (id3Size - buffer.Length > 0) ?
this.audioStream.Read(buffer, 0, buffer.Length) :
this.audioStream.Read(buffer, 0, id3Size);
id3Size -= bytesRead;
}
mpegFrame = new MpegFrame(this.audioStream);
}
else
{
// No ID3 tag present, presumably this is streaming and we are starting right at the Mp3 data.
// Assume the stream isn't seekable.
if (this.audioStream.Read(data, 3, 1) != 1)
{
goto cleanup;
}
mpegFrame = new MpegFrame(this.audioStream, data);
}
return mpegFrame;
// Cleanup and quit if you couldn't even read the initial data for some reason.
cleanup:
throw new Exception("Could not read intial audio stream data");
}
/// <summary>
/// Parses the passed in MediaStream to find the first frame and signals
/// to its parent MediaElement that it is ready to begin playback by calling
/// ReportOpenMediaCompleted.
/// </summary>
protected override void OpenMediaAsync()
{
// Initialize data structures to pass to the Media pipeline via the MediaStreamSource
Dictionary<MediaSourceAttributesKeys, string> mediaSourceAttributes = new Dictionary<MediaSourceAttributesKeys, string>();
Dictionary<MediaStreamAttributeKeys, string> mediaStreamAttributes = new Dictionary<MediaStreamAttributeKeys, string>();
List<MediaStreamDescription> mediaStreamDescriptions = new List<MediaStreamDescription>();
ThreadStart ts = new ThreadStart(ReadHeader);
Thread t = new Thread(ts);
t.Start();
do
{
System.Threading.Thread.Sleep(10);
}
while (mpegLayer3Frame == null && !readHeaderFail);
if (mpegLayer3Frame == null)
throw new InvalidOperationException("Header is unreadable");
// Mp3 frame validity check.
if (mpegLayer3Frame.FrameSize <= 0)
{
throw new InvalidOperationException("MpegFrame's FrameSize cannot be negative");
}
// Initialize the Mp3 data structures used by the Media pipeline with state from the first frame.
WaveFormatExtensible wfx = new WaveFormatExtensible();
this.MpegLayer3WaveFormat = new MpegLayer3WaveFormat();
this.MpegLayer3WaveFormat.WaveFormatExtensible = wfx;
this.MpegLayer3WaveFormat.WaveFormatExtensible.FormatTag = 85;
this.MpegLayer3WaveFormat.WaveFormatExtensible.Channels = (short)((mpegLayer3Frame.Channels == Channel.SingleChannel) ? 1 : 2);
this.MpegLayer3WaveFormat.WaveFormatExtensible.SamplesPerSec = mpegLayer3Frame.SamplingRate;
this.MpegLayer3WaveFormat.WaveFormatExtensible.AverageBytesPerSecond = mpegLayer3Frame.Bitrate / 8;
this.MpegLayer3WaveFormat.WaveFormatExtensible.BlockAlign = 1;
this.MpegLayer3WaveFormat.WaveFormatExtensible.BitsPerSample = 0;
this.MpegLayer3WaveFormat.WaveFormatExtensible.ExtraDataSize = 12;
this.MpegLayer3WaveFormat.Id = 1;
this.MpegLayer3WaveFormat.BitratePaddingMode = 0;
this.MpegLayer3WaveFormat.FramesPerBlock = 1;
this.MpegLayer3WaveFormat.BlockSize = (short)mpegLayer3Frame.FrameSize;
this.MpegLayer3WaveFormat.CodecDelay = 0;
mediaStreamAttributes[MediaStreamAttributeKeys.CodecPrivateData] = this.MpegLayer3WaveFormat.ToHexString();
this.audioStreamDescription = new MediaStreamDescription(MediaStreamType.Audio, mediaStreamAttributes);
mediaStreamDescriptions.Add(this.audioStreamDescription);
this.trackDuration = new TimeSpan(0, 0, (int)(this.audioStreamLength / MpegLayer3WaveFormat.WaveFormatExtensible.AverageBytesPerSecond));
mediaSourceAttributes[MediaSourceAttributesKeys.Duration] = this.trackDuration.Ticks.ToString(CultureInfo.InvariantCulture);
if (this.audioStream.CanSeek)
{
mediaSourceAttributes[MediaSourceAttributesKeys.CanSeek] = "1";
}
else
{
mediaSourceAttributes[MediaSourceAttributesKeys.CanSeek] = "0";
}
// Report that the Mp3MediaStreamSource has finished initializing its internal state and can now
// pass in Mp3 Samples.
this.ReportOpenMediaCompleted(mediaSourceAttributes, mediaStreamDescriptions);
this.currentFrame = mpegLayer3Frame;
this.currentFrameStartPosition = MpegFrame.FrameHeaderSize;
}
private void ReadHeader()
{
try
{
mpegLayer3Frame = this.ReadPastId3V2Tags();
}
catch
{
readHeaderFail = true;
}
}
/// <summary>
/// Parses the next sample from the requested stream and then calls ReportGetSampleCompleted
/// to inform its parent MediaElement of the next sample.
/// </summary>
/// <param name="mediaStreamType">
/// Should always be Audio for this MediaStreamSource.
/// </param>
protected override void GetSampleAsync(MediaStreamType mediaStreamType)
{
try
{
Dictionary<MediaSampleAttributeKeys, string> emptyDict = new Dictionary<MediaSampleAttributeKeys, string>();
MediaStreamSample audioSample = null;
if (this.currentFrame != null)
{
// Calculate our current position
double ratio = (double)this.currentFrameStartPosition / (double)this.audioStreamLength;
TimeSpan currentPosition = new TimeSpan((long)(this.trackDuration.Ticks * ratio));
// Create a MemoryStream to hold the bytes
// FrameSize includes the frame header which we've already read from the previous iteration, so just copy the
// header, and then read the remaining bytes
this.currentFrame.CopyHeader(buffer);
int audioSampleSize = this.currentFrame.FrameSize - MpegFrame.FrameHeaderSize;
int c = this.audioStream.Read(buffer, MpegFrame.FrameHeaderSize, audioSampleSize);
if (c != audioSampleSize)
{
// Ran out of bytes trying to read MP3 frame.
this.currentFrame = null;
audioSample = new MediaStreamSample(this.audioStreamDescription, null, 0, 0, 0, emptyDict);
this.ReportGetSampleCompleted(audioSample);
return;
}
this.currentFrameStartPosition += c;
using (MemoryStream audioFrameStream = new MemoryStream(buffer))
{
// Return the next sample in the stream
audioSample = new MediaStreamSample(this.audioStreamDescription, audioFrameStream, 0, this.currentFrame.FrameSize, currentPosition.Ticks, emptyDict);
this.ReportGetSampleCompleted(audioSample);
// Grab the next frame
MpegFrame nextFrame = new MpegFrame(this.audioStream);
if (nextFrame.Version == 1 && nextFrame.Layer == 3)
{
this.currentFrameStartPosition += MpegFrame.FrameHeaderSize;
this.currentFrame = nextFrame;
}
else
{
this.currentFrame = null;
}
}
}
else
{
// We're near the end of the file, or we got an irrecoverable error.
// Return a null stream which tells the MediaStreamSource & MediaElement to shut down
audioSample = new MediaStreamSample(this.audioStreamDescription, null, 0, 0, 0, emptyDict);
this.ReportGetSampleCompleted(audioSample);
}
}
catch (Exception ex)
{
}
}
/// <summary>
/// TODO FILL ME IN LATER
/// </summary>
protected override void CloseMedia()
{
try
{
this.audioStream.Close();
}
catch (CryptographicException)
{
// Ignore these, they are thrown when abruptly closing a
// stream (i.e. skipping tracks) where the source is a
// CryptoStream
}
catch (Exception e)
{
Debug.Assert(false, e.StackTrace);
}
}
/// <summary>
/// TODO FILL ME IN LATER
/// </summary>
/// <param name="diagnosticKind">
/// TODO FILL ME IN LATER . . .
/// </param>
protected override void GetDiagnosticAsync(MediaStreamSourceDiagnosticKind diagnosticKind)
{
throw new NotImplementedException();
}
/// <summary>
/// <para>
/// Effectively a Null-Op for when a MediaElement requests a seek at the beginning
/// of the stream. This makes the stream semi-unseekable.
/// </para>
/// <para>
/// In a fuller MediaStreamSource, the logic here would be to actually seek to
/// the correct mpeg frame matching the seekToTime passed in.
/// </para>
/// </summary>
/// <param name="seekToTime">
/// The time to seek to in nanosecond ticks.
/// </param>
protected override void SeekAsync(long seekToTime)
{
this.ReportSeekCompleted(seekToTime);
}
/// <summary>
/// TODO FILL ME IN LATER
/// </summary>
/// <param name="mediaStreamDescription">
/// TODO FILL ME IN LATER . . .
/// </param>
protected override void SwitchMediaStreamAsync(MediaStreamDescription mediaStreamDescription)
{
throw new NotImplementedException();
}
}