package org.jaudiotagger.audio.mp3;
import org.jaudiotagger.audio.exceptions.InvalidAudioFrameException;
import java.nio.ByteBuffer;
import java.util.Arrays;
/**
* Xing Frame
* <p/>
* <p>In some MP3s which variable bit rate the first frame in the file contains a special frame called a Xing Frame,
* instead of audio data. This is used to store additional information about the file. The most important aspect for
* this library is details allowing us to determine the bitrate of a Variable Bit Rate VBR file without having
* to process the whole file.
* <p/>
* Xing VBR Tag data format is 120 bytes long
* 4 bytes for Header Tag
* 4 bytes for Header Flags
* 4 bytes for FRAME SIZE
* 4 bytes for AUDIO_SIZE
* 100 bytes for entry (NUMTOCENTRIES)
* 4 bytes for VBR SCALE. a VBR quality indicator: 0=best 100=worst
* <p/>
* It my then contain a Lame Frame ( a Lame frame is in essence an extended Xing Frame
*/
public class XingFrame
{
//The offset into first frame varies based on the MPEG frame properties
private static final int MPEG_VERSION_1_MODE_MONO_OFFSET = 21;
private static final int MPEG_VERSION_1_MODE_STEREO_OFFSET = 36;
private static final int MPEG_VERSION_2_MODE_MONO_OFFSET = 13;
private static final int MPEG_VERSION_2_MODE_STEREO_OFFSET = 21;
private static final int XING_HEADER_BUFFER_SIZE = 120;
private static final int XING_IDENTIFIER_BUFFER_SIZE = 4;
private static final int XING_FLAG_BUFFER_SIZE = 4;
private static final int XING_FRAMECOUNT_BUFFER_SIZE = 4;
private static final int XING_AUDIOSIZE_BUFFER_SIZE = 4;
public static final int MAX_BUFFER_SIZE_NEEDED_TO_READ_XING = MPEG_VERSION_1_MODE_STEREO_OFFSET + XING_HEADER_BUFFER_SIZE + LameFrame.LAME_HEADER_BUFFER_SIZE;
private static final int BYTE_1 = 0;
private static final int BYTE_2 = 1;
private static final int BYTE_3 = 2;
private static final int BYTE_4 = 3;
/**
* Use when it is a VBR (Variable Bitrate) file
*/
private static final byte[] XING_VBR_ID = {'X', 'i', 'n', 'g'};
/**
* Use when it is a CBR (Constant Bitrate) file
*/
private static final byte[] XING_CBR_ID = {'I', 'n', 'f', 'o'};
private ByteBuffer header;
private boolean vbr = false;
private boolean isFrameCountEnabled = false;
private int frameCount = -1;
private boolean isAudioSizeEnabled = false;
private int audioSize = -1;
private LameFrame lameFrame;
/**
* Read the Xing Properties from the buffer
*/
private XingFrame(ByteBuffer header)
{
this.header=header;
//Go to start of Buffer
header.rewind();
//Set Vbr
setVbr();
//Read Flags, only the fourth byte of interest to us
byte flagBuffer[] = new byte[XING_FLAG_BUFFER_SIZE];
header.get(flagBuffer);
//Read FrameCount if flag set
if ((flagBuffer[BYTE_4] & (byte) (1)) != 0)
{
setFrameCount();
}
//Read Size if flag set
if ((flagBuffer[BYTE_4] & (byte) (1 << 1)) != 0)
{
setAudioSize();
}
//TODO TOC
//TODO VBR Quality
//Look for LAME Header as long as we have enough bytes to do it properly
if (header.limit() >= XING_HEADER_BUFFER_SIZE + LameFrame.LAME_HEADER_BUFFER_SIZE)
{
header.position(XING_HEADER_BUFFER_SIZE);
lameFrame = LameFrame.parseLameFrame(header);
}
}
public LameFrame getLameFrame()
{
return lameFrame;
}
/**
* Set whether or not VBR, (Xing can also be used for CBR though this is less useful)
*/
private void setVbr()
{
//Is it VBR or CBR
byte[] identifier = new byte[XING_IDENTIFIER_BUFFER_SIZE];
header.get(identifier);
if (Arrays.equals(identifier, XING_VBR_ID))
{
MP3File.logger.finest("Is Vbr");
vbr = true;
}
}
/**
* Set count of frames
*/
private void setFrameCount()
{
byte frameCountBuffer[] = new byte[XING_FRAMECOUNT_BUFFER_SIZE];
header.get(frameCountBuffer);
isFrameCountEnabled = true;
frameCount = (frameCountBuffer[BYTE_1] << 24) & 0xFF000000 | (frameCountBuffer[BYTE_2] << 16) & 0x00FF0000 | (frameCountBuffer[BYTE_3] << 8) & 0x0000FF00 | frameCountBuffer[BYTE_4] & 0x000000FF;
}
/**
* @return true if frameCount has been specified in header
*/
public final boolean isFrameCountEnabled()
{
return isFrameCountEnabled;
}
/**
* @return count of frames
*/
public final int getFrameCount()
{
return frameCount;
}
/**
* Set size of AudioData
*/
private void setAudioSize()
{
byte frameSizeBuffer[] = new byte[XING_AUDIOSIZE_BUFFER_SIZE];
header.get(frameSizeBuffer);
isAudioSizeEnabled = true;
audioSize = (frameSizeBuffer[BYTE_1] << 24) & 0xFF000000 | (frameSizeBuffer[BYTE_2] << 16) & 0x00FF0000 | (frameSizeBuffer[BYTE_3] << 8) & 0x0000FF00 | frameSizeBuffer[BYTE_4] & 0x000000FF;
}
/**
* @return true if audioSize has been specified in header
*/
public final boolean isAudioSizeEnabled()
{
return isAudioSizeEnabled;
}
/**
* @return size of audio data in bytes
*/
public final int getAudioSize()
{
return audioSize;
}
/**
* Parse the XingFrame of an MP3File, cannot be called until we have validated that
* this is a XingFrame
*
* @return
* @throws InvalidAudioFrameException
*/
public static XingFrame parseXingFrame(ByteBuffer header) throws InvalidAudioFrameException
{
XingFrame xingFrame = new XingFrame(header);
return xingFrame;
}
/**
* IS this a Xing frame
*
* @param bb
* @param mpegFrameHeader
* @return true if this is a Xing frame
*/
public static ByteBuffer isXingFrame(ByteBuffer bb, MPEGFrameHeader mpegFrameHeader)
{
//We store this so can return here after scanning through buffer
int startPosition = bb.position();
//Get to Start of where Xing Frame Should be ( we dont know if it is one at this point)
if (mpegFrameHeader.getVersion() == MPEGFrameHeader.VERSION_1)
{
if (mpegFrameHeader.getChannelMode() == MPEGFrameHeader.MODE_MONO)
{
bb.position(startPosition + MPEG_VERSION_1_MODE_MONO_OFFSET);
}
else
{
bb.position(startPosition + MPEG_VERSION_1_MODE_STEREO_OFFSET);
}
}
//MPEGVersion 2 and 2.5
else
{
if (mpegFrameHeader.getChannelMode() == MPEGFrameHeader.MODE_MONO)
{
bb.position(startPosition + MPEG_VERSION_2_MODE_MONO_OFFSET);
}
else
{
bb.position(startPosition + MPEG_VERSION_2_MODE_STEREO_OFFSET);
}
}
//Create header from here
ByteBuffer header = bb.slice();
// Return Buffer to start Point
bb.position(startPosition);
//Check Identifier
byte[] identifier = new byte[XING_IDENTIFIER_BUFFER_SIZE];
header.get(identifier);
if ((!Arrays.equals(identifier, XING_VBR_ID)) && (!Arrays.equals(identifier, XING_CBR_ID)))
{
return null;
}
MP3File.logger.finest("Found Xing Frame");
return header;
}
/**
* Is this XingFrame detailing a variable bit rate MPEG
*
* @return
*/
public final boolean isVbr()
{
return vbr;
}
/**
* @return a string representation
*/
public String toString()
{
return "xingheader" + " vbr:" + vbr + " frameCountEnabled:" + isFrameCountEnabled + " frameCount:" + frameCount + " audioSizeEnabled:" + isAudioSizeEnabled + " audioFileSize:" + audioSize;
}
}
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