/// <summary>
/// Constructs and initializes a new instance of <see
/// cref="AudioHeader" /> by populating it with specified
/// values.
/// </summary>
/// <param name="flags">
/// A <see cref="uint" /> value specifying flags for the new
/// instance.
/// </param>
/// <param name="streamLength">
/// A <see cref="long" /> value specifying the stream length
/// of the new instance.
/// </param>
/// <param name="xingHeader">
/// A <see cref="XingHeader" /> object representing the Xing
/// header associated with the new instance.
/// </param>
/// <param name="vbriHeader">
/// A <see cref="VBRIHeader" /> object representing the VBRI
/// header associated with the new instance.
/// </param>
private AudioHeader(uint flags, long streamLength,
XingHeader xingHeader,
VBRIHeader vbriHeader)
{
this.flags = flags;
this.stream_length = streamLength;
this.xing_header = xingHeader;
this.vbri_header = vbriHeader;
this.duration = TimeSpan.Zero;
}
/// <summary>
/// Constructs and initializes a new instance of <see
/// cref="AudioHeader" /> by reading its contents from a
/// <see cref="ByteVector" /> object and its Xing Header from
/// the appropriate location in the specified file.
/// </summary>
/// <param name="data">
/// A <see cref="ByteVector" /> object containing the header
/// to read.
/// </param>
/// <param name="file">
/// A <see cref="TagLibSharp.File" /> object to read the Xing
/// header from.
/// </param>
/// <param name="position">
/// A <see cref="long" /> value indicating the position in
/// <paramref name="file" /> at which the header begins.
/// </param>
/// <exception cref="CorruptFileException">
/// <paramref name="data" /> is less than 4 bytes long,
/// does not begin with a MPEG audio synch, has a negative
/// bitrate, or has a sample rate of zero.
/// </exception>
private AudioHeader(ByteVector data, TagLibSharp.File file,
long position)
{
this.duration = TimeSpan.Zero;
stream_length = 0;
if (data.Count < 4)
{
throw new CorruptFileException(
"Insufficient header length.");
}
if (data [0] != 0xFF)
{
throw new CorruptFileException(
"First byte did not match MPEG synch.");
}
// Checking bits from high to low:
//
// First 3 bits MUST be set. Bits 4 and 5 can
// be 00, 10, or 11 but not 01. One or more of
// bits 6 and 7 must be set. Bit 8 can be
// anything.
if ((data [1] & 0xE6) <= 0xE0 || (data [1] & 0x18) == 0x08)
{
throw new CorruptFileException(
"Second byte did not match MPEG synch.");
}
flags = data.ToUInt();
if (((flags >> 12) & 0x0F) == 0x0F)
{
throw new CorruptFileException(
"Header uses invalid bitrate index.");
}
if (((flags >> 10) & 0x03) == 0x03)
{
throw new CorruptFileException(
"Invalid sample rate.");
}
xing_header = XingHeader.Unknown;
vbri_header = VBRIHeader.Unknown;
// Check for a Xing header that will help us in
// gathering information about a VBR stream.
file.Seek(position + XingHeader.XingHeaderOffset(
Version, ChannelMode));
ByteVector xing_data = file.ReadBlock(16);
if (xing_data.Count == 16 && xing_data.StartsWith(
XingHeader.FileIdentifier))
{
xing_header = new XingHeader(xing_data);
}
if (xing_header.Present)
{
return;
}
// A Xing header could not be found, next chec for a
// Fraunhofer VBRI header.
file.Seek(position + VBRIHeader.VBRIHeaderOffset());
// Only get the first 24 bytes of the Header.
// We're not interested in the TOC entries.
ByteVector vbri_data = file.ReadBlock(24);
if (vbri_data.Count == 24 &&
vbri_data.StartsWith(VBRIHeader.FileIdentifier))
{
vbri_header = new VBRIHeader(vbri_data);
}
}