/// <summary>
/// Reads an audio packet, assigning the audio header and
/// advancing the position to the next packet position.
/// </summary>
/// <param name="position">
/// A <see cref="long" /> value reference specifying the
/// position at which to start reading the packet. This value
/// is updated to the position of the next packet.
/// </param>
void ReadAudioPacket(ref long position)
{
Seek(position + 4);
int length = ReadBlock(2).ToUShort();
if (!audio_found)
{
// There is a maximum of 16 stuffing bytes, read up to the PTS/DTS flags
ByteVector packetHeaderBytes = this.ReadBlock(19);
int i = 0;
while (i < packetHeaderBytes.Count && packetHeaderBytes[i] == 0xFF)
{
// Byte is a stuffing byte
i++;
}
if ((packetHeaderBytes[i] & 0x40) != 0)
{
// STD buffer size is unexpected for audio packets, but whatever
i++;
}
// Decode the PTS/DTS flags
byte timestampFlags = packetHeaderBytes[i];
long dataOffset = 4 + 2 + i + // Packet marker + packet length + stuffing bytes/STD buffer size
((timestampFlags & 0x20) > 0 ? 4 : 0) + // Presentation timestamp
((timestampFlags & 0x10) > 0 ? 4 : 0); // Decode timestamp
audio_found = AudioHeader.Find(out audio_header, this, position + dataOffset, length - 9);
}
position += length;
}
protected override void ReadStart(long start, ReadStyle propertiesStyle)
{
if (propertiesStyle != ReadStyle.None && !AudioHeader.Find(out first_header, this, start, 0x4000))
{
throw new CorruptFileException("MPEG audio header not found.");
}
}
/// <summary>
/// Reads format specific information at the start of the
/// file.
/// </summary>
/// <param name="start">
/// A <see cref="long" /> value containing the seek position
/// at which the tags end and the media data begins.
/// </param>
/// <param name="propertiesStyle">
/// A <see cref="ReadStyle" /> value specifying at what level
/// of accuracy to read the media properties, or <see
/// cref="ReadStyle.None" /> to ignore the properties.
/// </param>
/// <remarks>
/// This method only searches for an audio header in the
/// first 16384 bytes of code to avoid searching forever in
/// corrupt files.
/// </remarks>
protected override void ReadStart(long start, ReadStyle propertiesStyle)
{
// Only check the first 16 bytes so we're not stuck
// reading a bad file forever.
if ((propertiesStyle & ReadStyle.Average) != 0 &&
!AudioHeader.Find(out first_header, this, start, 0x4000))
{
throw new CorruptFileException("MPEG audio header not found.");
}
}
/// <summary>
/// Reads an audio packet, assigning the audio header and
/// advancing the position to the next packet position.
/// </summary>
/// <param name="position">
/// A <see cref="long" /> value reference specifying the
/// position at which to start reading the packet. This value
/// is updated to the position of the next packet.
/// </param>
void ReadAudioPacket(ref long position)
{
Seek(position + 4);
int length = ReadBlock(2).ToUShort();
if (!audio_found)
{
audio_found = AudioHeader.Find(out audio_header, this, position + 15, length - 9);
}
position += length;
}