File	Doc	Category	Size	Date	Package
ID3Unsynchronization.java	API Doc	Jaudiotagger 2.0.4	9189	Wed Mar 30 16:12:06 BST 2011	org.jaudiotagger.tag.id3

ID3Unsynchronization

• java.lang.Object

Fields Summary
public static Logger	logger

Constructors Summary

Methods Summary
public static boolean	requiresUnsynchronization(byte[] abySource) Check if a byte array will require unsynchronization before being written as a tag. If the byte array contains any $FF $E0 bytes, then it will require unsynchronization. param abySource the byte array to be examined return true if unsynchronization is required, false otherwise for (int i = 0; i < abySource.length - 1; i++) { if (((abySource[i] & MPEGFrameHeader.SYNC_BYTE1) == MPEGFrameHeader.SYNC_BYTE1) && ((abySource[i + 1] & MPEGFrameHeader.SYNC_BYTE2) == MPEGFrameHeader.SYNC_BYTE2)) { if (logger.isLoggable(Level.FINEST)) { logger.finest("Unsynchronisation required found bit at:" + i); } return true; } } return false;
public static java.nio.ByteBuffer	synchronize(java.nio.ByteBuffer source) Synchronize an array of bytes, this should only be called if it has been determined the tag is unsynchronised Any patterns of the form $FF $00 should be replaced by $FF param source a ByteBuffer to be unsynchronized return a synchronized representation of the source //long start = System.nanoTime(); int len = source.remaining(); byte[] bytes = new byte[len + 1]; // an extra byte saves a check later. source.get(bytes, 0, len); int from = 0, to = 0; boolean copy = true; // whether to copy the byte, if false, check the byte != 0. while (from < len) { byte byteValue = bytes[from++]; if (copy || byteValue != 0) bytes[to++] = byteValue; copy = ((byteValue & MPEGFrameHeader.SYNC_BYTE1) != MPEGFrameHeader.SYNC_BYTE1); } ByteBuffer bb2 = ByteBuffer.wrap(bytes, 0, to); //long time = System.nanoTime() - start; //System.out.printf("Took %6.3f ms, was %d bytes, now %,d bytes%n", time/1e6, source.limit(), bb2.limit()); return bb2;
public static byte[]	unsynchronize(byte[] abySource) Unsynchronize an array of bytes, this should only be called if the decision has already been made to unsynchronize the byte array In order to prevent a media player from incorrectly interpreting the contents of a tag, all $FF bytes followed by a byte with value >=224 must be followed by a $00 byte (thus, $FF $F0 sequences become $FF $00 $F0). Additionally because unsynchronisation is being applied any existing $FF $00 have to be converted to $FF $00 $00 param abySource a byte array to be unsynchronized return a unsynchronized representation of the source ByteArrayInputStream input = new ByteArrayInputStream(abySource); ByteArrayOutputStream output = new ByteArrayOutputStream(abySource.length); int count = 0; while (input.available() > 0) { int firstByte = input.read(); count++; output.write(firstByte); if ((firstByte & MPEGFrameHeader.SYNC_BYTE1) == MPEGFrameHeader.SYNC_BYTE1) { // if byte is $FF, we must check the following byte if there is one if (input.available() > 0) { input.mark(1); // remember where we were, if we don't need to unsynchronize int secondByte = input.read(); if ((secondByte & MPEGFrameHeader.SYNC_BYTE2) == MPEGFrameHeader.SYNC_BYTE2) { // we need to unsynchronize here if (logger.isLoggable(Level.FINEST)) { logger.finest("Writing unsynchronisation bit at:" + count); } output.write(0); } else if (secondByte == 0) { // we need to unsynchronize here if (logger.isLoggable(Level.FINEST)) { logger.finest("Inserting zero unsynchronisation bit at:" + count); } output.write(0); } input.reset(); } } } // if we needed to unsynchronize anything, and this tag ends with 0xff, we have to append a zero byte, // which will be removed on de-unsynchronization later if ((abySource[abySource.length - 1] & MPEGFrameHeader.SYNC_BYTE1) == MPEGFrameHeader.SYNC_BYTE1) { logger.finest("Adding unsynchronisation bit at end of stream"); output.write(0); } return output.toByteArray();