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VbriFrame.javaAPI DocJaudiotagger 2.0.46463Mon Sep 12 16:08:14 BST 2011org.jaudiotagger.audio.mp3

VbriFrame

public class VbriFrame extends Object
Vrbi Frame

In MP3s encoded using the franhofer encoder which variable bit rate the first frame in the file contains a special frame called a Vrbi Frame, instead of audio data (Other Vbr encoders use the more common Xing Frame). 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.

From http://www.codeproject.com/KB/audio-video/mpegaudioinfo.aspx#SideInfo

This header is only used by MPEG audio files encoded with the Fraunhofer Encoder as far as I know. It is different from the XING header. You find it exactly 32 bytes after the end of the first MPEG audio header in the file. (Note that the position is zero-based; position, length and example are each in byte-format.) Position Length Meaning Example 0 4 VBR header ID in 4 ASCII chars, always 'VBRI', not NULL-terminated 'VBRI' 4 2 Version ID as Big-Endian WORD 1 6 2 Delay as Big-Endian float 7344 8 2 Quality indicator 75 10 4 Number of Bytes of Audio as Big-Endian DWORD 45000 14 4 Number of Frames as Big-Endian DWORD 7344 18 2 Number of entries within TOC table as Big-Endian WORD 100 20 2 Scale factor of TOC table entries as Big-Endian DWORD 1 22 2 Size per table entry in bytes (max 4) as Big-Endian WORD 2 24 2 Frames per table entry as Big-Endian WORD 845 26 TOC entries for seeking as Big-Endian integral. From size per table entry and number of entries, you can calculate the length of this field.

Fields Summary
private static final int
VBRI_OFFSET
private static final int
VBRI_HEADER_BUFFER_SIZE
private static final int
VBRI_IDENTIFIER_BUFFER_SIZE
private static final int
VBRI_DELAY_BUFFER_SIZE
private static final int
VBRI_QUALITY_BUFFER_SIZE
private static final int
VBRI_AUDIOSIZE_BUFFER_SIZE
private static final int
VBRI_FRAMECOUNT_BUFFER_SIZE
private static final int
VBRI_TOC_ENTRY_BUFFER_SIZE
public static final int
MAX_BUFFER_SIZE_NEEDED_TO_READ_VBRI
private static final int
BYTE_1
private static final int
BYTE_2
private static final int
BYTE_3
private static final int
BYTE_4
private static final byte[]
VBRI_VBR_ID
Identifier
private ByteBuffer
header
private boolean
vbr
private int
frameCount
private int
audioSize
private LameFrame
lameFrame
Constructors Summary
private VbriFrame(ByteBuffer header)
Read the VBRI Properties from the buffer


                
      
    
        this.header=header;
        //Go to start of Buffer
        header.rewind();
        header.position(10);
        setAudioSize();
        setFrameCount();
Methods Summary
public final intgetAudioSize()

return
size of audio data in bytes

        return audioSize;
public java.lang.StringgetEncoder()

        return "Fraunhofer";
public final intgetFrameCount()

return
count of frames

        return frameCount;
public final booleanisVbr()
Is this VBRIFrame detailing a varaible bit rate MPEG

return

        return true;
public static java.nio.ByteBufferisVbriFrame(java.nio.ByteBuffer bb, MPEGFrameHeader mpegFrameHeader)
IS this a VBRI frame

param
bb
param
mpegFrameHeader
return
raw header if this is a VBRI frame


        //We store this so can return here after scanning through buffer
        int startPosition = bb.position();
        MP3File.logger.finest("Checking VBRI Frame at" + startPosition);

        bb.position(startPosition + VBRI_OFFSET);

        //Create header from here
        ByteBuffer header = bb.slice();

        // Return Buffer to start Point
        bb.position(startPosition);

        //Check Identifier
        byte[] identifier = new byte[VBRI_IDENTIFIER_BUFFER_SIZE];
        header.get(identifier);
        if ((!Arrays.equals(identifier, VBRI_VBR_ID)))
        {
            return null;
        }
        MP3File.logger.finest("Found VBRI Frame");
        return header;
public static org.jaudiotagger.audio.mp3.VbriFrameparseVBRIFrame(java.nio.ByteBuffer header)
Parse the VBRIFrame of an MP3File, cannot be called until we have validated that this is a VBRIFrame

return
throws
org.jaudiotagger.audio.exceptions.InvalidAudioFrameException

        VbriFrame VBRIFrame = new VbriFrame(header);
        return VBRIFrame;
private voidsetAudioSize()
Set size of AudioData

        byte frameSizeBuffer[] = new byte[VBRI_AUDIOSIZE_BUFFER_SIZE];
        header.get(frameSizeBuffer);
        boolean audioSizeEnabled = true;
        audioSize = (frameSizeBuffer[BYTE_1] << 24) & 0xFF000000 | (frameSizeBuffer[BYTE_2] << 16) & 0x00FF0000 | (frameSizeBuffer[BYTE_3] << 8) & 0x0000FF00 | frameSizeBuffer[BYTE_4] & 0x000000FF;
private voidsetFrameCount()
Set count of frames

        byte frameCountBuffer[] = new byte[VBRI_FRAMECOUNT_BUFFER_SIZE];
        header.get(frameCountBuffer);
        boolean frameCountEnabled = true;
        frameCount = (frameCountBuffer[BYTE_1] << 24) & 0xFF000000 | (frameCountBuffer[BYTE_2] << 16) & 0x00FF0000 | (frameCountBuffer[BYTE_3] << 8) & 0x0000FF00 | frameCountBuffer[BYTE_4] & 0x000000FF;
public java.lang.StringtoString()

return
a string represntation

        return "VBRIheader" + " vbr:" + vbr + " frameCount:" + frameCount + " audioFileSize:" + audioSize + " encoder:" + getEncoder();