/// <summary>Begins the decoding process.</summary>
/// <param name="source">The source.</param>
/// <exception cref="NotSupportedException">Only Layer 3 Audio is supported!.</exception>
/// <exception cref="Exception">Decoding already started!.</exception>
public override void BeginDecode(IFrameSource source)
{
if (m_FrameDecoder != null)
{
Close();
}
SourceName = source.Name;
m_Source = source;
// get first audio frame
MP3AudioFrame l_MP3Frame = ReadNextAudioFrame();
if (l_MP3Frame.Header.Layer != MP3AudioFrameLayer.Layer3)
{
throw new NotSupportedException("Source " + SourceName + ": Only Layer 3 Audio is supported!");
}
// prepare decoder
m_OutputChannels = l_MP3Frame.Header.ChannelCount;
float[] isEqualizerFactors = m_Equalizer.GetFactors();
m_Filter1 = new MP3AudioSynthesisFilter(0, 32000.0f, isEqualizerFactors);
if (m_OutputChannels == 2)
{
m_Filter2 = new MP3AudioSynthesisFilter(1, 32000.0f, isEqualizerFactors);
}
m_SamplingRate = l_MP3Frame.Header.SamplingRate;
m_OutputBuffer = new MP3AudioStereoBuffer(m_SamplingRate);
m_FrameDecoder = new MP3AudioLayerIIIDecoder(l_MP3Frame.Header, m_Filter1, m_Filter2, m_OutputBuffer, (int)MP3AudioOutputMode.Both);
DecodeFrame(l_MP3Frame);
}
/// <summary>
/// Reads a frame from the MP3 stream.
/// Returns whether the operation was successful.
/// </summary>
bool DecodeFrame(MP3AudioFrame frame)
{
if (frame == null)
{
return(false);
}
try
{
m_OutputBuffer.Clear();
m_FrameDecoder.DecodeFrame(frame);
m_Resetted = false;
return(true);
}
catch (Exception ex)
{
if (!m_Resetted)
{
m_FrameDecoder.Reset();
m_Resetted = true;
}
Trace.WriteLine("Source " + SourceName + ": Error while decoding mp3 frame.\n" + ex);
return(false);
}
}
/// <summary>Reads the next audio frame and silently skips garbage and invalid frames.</summary>
/// <returns></returns>
MP3AudioFrame ReadNextAudioFrame()
{
MP3AudioFrame l_MP3Frame = null;
while (l_MP3Frame == null)
{
AudioFrame frame = m_Source.GetNextFrame();
// eof ?
if (frame == null)
{
return(null);
}
OnDecoding(frame);
l_MP3Frame = frame as MP3AudioFrame;
}
return(l_MP3Frame);
}
/// <summary>
/// Gets the next frame.
/// </summary>
/// <returns>Returns the next frame or null (at end of stream).</returns>
public AudioFrame GetNextFrame()
{
while (true)
{
#region return buffered frames first (if any)
// got a decoded frame at the cache ?
if (m_BufferedFrame != null)
{
AudioFrame result;
if (m_InvalidFrame != null)
{
result = m_InvalidFrame;
m_InvalidFrame = null;
}
else
{
result = m_BufferedFrame;
m_BufferedFrame = null;
}
return(result);
}
#endregion
#region search next frame start
// search the next interesting position
var searchResult = FindFrame();
if (searchResult == null)
{
#region end of stream cleanup
// invalid data at end of stream ?
if (m_Reader.Available > 0)
{
// yes buffer
InvalidData(m_Reader.GetBuffer());
}
// got an invalid frame ?
if (m_InvalidFrame != null)
{
// return invalid frame
AudioFrame result = m_InvalidFrame;
m_InvalidFrame = null;
return(result);
}
// got an id3v1 ?
if (m_ID3v1 != null)
{
// return id3v1
AudioFrame result = m_ID3v1;
m_ID3v1 = null;
return(result);
}
// everything done, return null
return(null);
#endregion
}
#endregion
#region check search result
// got garbage at the beginning?
if (searchResult.Index > 0)
{
// yes, invalid data
InvalidData(m_Reader.GetBuffer(searchResult.Index));
continue;
}
#endregion
#region decode frame
// try to decode frame
try
{
var valid = false;
AudioFrame frame = null;
switch (searchResult.Match)
{
#region decode mp3 frame
case MatchType.MP3Frame:
var audioFrame = new MP3AudioFrame();
valid = audioFrame.Parse(m_Reader);
frame = audioFrame;
break;
#endregion
#region decode id3 frame
case MatchType.ID3Frame:
frame = new ID3v2();
valid = frame.Parse(m_Reader);
break;
#endregion
default: throw new NotImplementedException(string.Format("Unknown frame type {0}", searchResult.Match));
}
// parsed successfully?
if (valid)
{
// yes, cache frame
m_BufferedFrame = frame;
}
else
{
// no invalidate
InvalidData(m_Reader.GetBuffer(1));
}
}
catch (Exception ex)
{
Trace.TraceError(string.Format("Error while decoding {0} in stream {1}", searchResult.Match, m_Reader));
Trace.TraceError(ex.ToString());
// invalid frame or decoder error, move ahead
var count = (searchResult.Index < 0) ? 1 : searchResult.Index + 1;
InvalidData(m_Reader.GetBuffer(count));
}
#endregion
}
}