My Java program needs to send a binary payload via QR Code, but I can't get it to work. I have tried several QR Code libraries and many approaches, but all seem to have this problem. My current implementation uses ZXING.
The problem is that all the Java libraries I've tried seem to be focused on String payloads, and do not provide support for binary data. The common suggested solution to this is to encode the binary data as Base64. However, my data is already near the size limit of QR Codes. With the 33% inflation caused by Base64 encoding, my data is too big. I have already expended significant effort into reducing the size of the payload, and it currently consists of 4 character hashes delimited by new lines; all inside max level compression by the Java Deflator class. I can't make it any smaller.
I need a way to store binary data in a QR code with minimal data inflation overhead.
Update:
I recently went back and published the referenced code as a project on GitHub for anyone who wants to use it.
https://github.com/yurelle/Base45Encoder
I developed a solution which only introduces a storage efficiency loss of -8%. It exploits a built-in compression optimization of the ZXING QR Code Library.
Explanation
ZXING will automatically detect if your String payload is purely AlphaNumeric (by their own definition), and if so, it will automatically compress 2 AlphaNumeric characters into 11 bits. The definition ZXING uses for "alphanumeric" is all-caps only, 0-9, and a few special symbols ('/', ':', etc.). All told, their definition allows 45 possible values. Then, it packs 2 of these Base45 digits into 11 bits.
2 digits in base 45 is 2,025 possible values. 11 bits has a maximum storage capacity of 2,048 possible states. This is only a loss of 1.1% in storage efficiency behind raw binary.
45 ^ 2 = 2,025
2 ^ 11 = 2,048
2,048 - 2,025 = 23
23 / 2,048 = 0.01123046875 = 1.123%
However, this is the ideal / theoretical efficiency. My implementation processes data in chunks, using a Long as a computational buffer. However, since Java Long's are singed, we can only use the lower 7 bytes. The conversion code requires continuously positive values; using the highest 8th byte would contaminate the sign bit and randomly produce negative values.
Real-World Test:
Using a 7 byte Long to encode a 2KB buffer of random bytes, we get the following results.
Raw Binary Size: 2,048
Encoded String Size: 3,218
QR Code Alphanum Size: 2,213 (after the QR Code compresses 2 base45 digits to 11 bits)
This is a real-world storage efficiency loss of only 8%.
2,213 - 2,048 = 165
165 / 2,048 = 0.08056640625 = 8.0566%
Solution
I implemented it as a self-contained static utility class, so all you have to do is call:
//Encode
final byte[] myBinaryData = ...;
final String encodedStr = BinaryToBase45Encoder.encodeToBase45QrPayload(myBinaryData);
//Decode
final byte[] decodedBytes = BinaryToBase45Encoder.decodeBase45QrPayload(encodedStr);
Alternatively, you can also do it via InputStreams:
//Encode
final InputStream in_1 = ... ;
final String encodedStr = BinaryToBase45Encoder.encodeToBase45QrPayload(in_1);
//Decode
final InputStream in_2 = ... ;
final byte[] decodedBytes = BinaryToBase45Encoder.decodeBase45QrPayload(in_2);
Here's the implementation
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
/**
* For some reason none of the Java QR Code libraries support binary payloads. At least, none that
* I could find anyway. The commonly suggested workaround for this is to use Base64 encoding.
* However, this results in a 33% payload size inflation. If your payload is already near the size
* limit of QR codes, this is a lot.
*
* This class implements an encoder which takes advantage of a built-in compression optimization
* of the ZXING QR Code library, to enable the storage of Binary data into a QR Code, with a
* storage efficiency loss of only -8%.
*
* The built-in optimization is this: ZXING will automatically detect if your String payload is
* purely AlphaNumeric (by their own definition), and if so, it will automatically compress 2
* AlphaNumeric characters into 11 bits.
*
*
* ----------------------
*
*
* The included ALPHANUMERIC_TABLE is the conversion table used by the ZXING library as a reverse
* index for determining if a given input data should be classified as alphanumeric.
*
* See:
*
* com.google.zxing.qrcode.encoder.Encoder.chooseMode(String content, String encoding)
*
* which scans through the input string one character at a time and passes them to:
*
* getAlphanumericCode(int code)
*
* in the same class, which uses that character as a numeric index into the the
* ALPHANUMERIC_TABLE.
*
* If you examine the values, you'll notice that it ignores / disqualifies certain values, and
* effectively converts the input into base 45 (0 -> 44; -1 is interpreted by the calling code
* to mean a failure). This is confirmed in the function:
*
* appendAlphanumericBytes(CharSequence content, BitArray bits)
*
* where they pack 2 of these base 45 digits into 11 bits. This presents us with an opportunity.
* If we can take our data, and convert it into a compatible base 45 alphanumeric representation,
* then the QR Encoder will automatically pack that data into sub-byte chunks.
*
* 2 digits in base 45 is 2,025 possible values. 11 bits has a maximum storage capacity of 2,048
* possible states. This is only a loss of 1.1% in storage efficiency behind raw binary.
*
* 45 ^ 2 = 2,025
* 2 ^ 11 = 2,048
* 2,048 - 2,025 = 23
* 23 / 2,048 = 0.01123046875 = 1.123%
*
* However, this is the ideal / theoretical efficiency. This implementation processes data in
* chunks, using a Long as a computational buffer. However, since Java Long's are singed, we
* can only use the lower 7 bytes. The conversion code requires continuously positive values;
* using the highest 8th byte would contaminate the sign bit and randomly produce negative
* values.
*
*
* Real-World Test:
*
* Using a 7 byte Long to encode a 2KB buffer of random bytes, we get the following results.
*
* Raw Binary Size: 2,048
* Encoded String Size: 3,218
* QR Code Alphanum Size: 2,213 (after the QR Code compresses 2 base45 digits to 11 bits)
*
* This is a real-world storage efficiency loss of only 8%.
*
* 2,213 - 2,048 = 165
* 165 / 2,048 = 0.08056640625 = 8.0566%
*/
public class BinaryToBase45Encoder {
public final static int[] ALPHANUMERIC_TABLE;
/*
* You could probably just copy & paste the array literal from the ZXING source code; it's only
* an array definition. But I was unsure of the licensing issues with posting it on the internet,
* so I did it this way.
*/
static {
final Field SOURCE_ALPHANUMERIC_TABLE;
int[] tmp;
//Copy lookup table from ZXING Encoder class
try {
SOURCE_ALPHANUMERIC_TABLE = com.google.zxing.qrcode.encoder.Encoder.class.getDeclaredField("ALPHANUMERIC_TABLE");
SOURCE_ALPHANUMERIC_TABLE.setAccessible(true);
tmp = (int[]) SOURCE_ALPHANUMERIC_TABLE.get(null);
} catch (NoSuchFieldException e) {
e.printStackTrace();//Shouldn't happen
tmp = null;
} catch (IllegalAccessException e) {
e.printStackTrace();//Shouldn't happen
tmp = null;
}
//Store
ALPHANUMERIC_TABLE = tmp;
}
public static final int NUM_DISTINCT_ALPHANUM_VALUES = 45;
public static final char[] alphaNumReverseIndex = new char[NUM_DISTINCT_ALPHANUM_VALUES];
static {
//Build AlphaNum Index
final int len = ALPHANUMERIC_TABLE.length;
for (int x = 0; x < len; x++) {
// The base45 result which the alphanum lookup table produces.
// i.e. the base45 digit value which String characters are
// converted into.
//
// We use this value to build a reverse lookup table to find
// the String character we have to send to the encoder, to
// make it produce the given base45 digit value.
final int base45DigitValue = ALPHANUMERIC_TABLE[x];
//Ignore the -1 records
if (base45DigitValue > -1) {
//The index into the lookup table which produces the given base45 digit value.
//
//i.e. to produce a base45 digit with the numeric value in base45DigitValue, we need
//to send the Encoder a String character with the numeric value in x.
alphaNumReverseIndex[base45DigitValue] = (char) x;
}
}
}
/*
* The storage capacity of one digit in the number system; i.e. the maximum
* possible number of distinct values which can be stored in 1 logical digit
*/
public static final int QR_PAYLOAD_NUMERIC_BASE = NUM_DISTINCT_ALPHANUM_VALUES;
/*
* We can't use all 8 bytes, because the Long is signed, and the conversion math
* requires consistently positive values. If we populated all 8 bytes, then the
* last byte has the potential to contaminate the sign bit, and break the
* conversion math. So, we only use the lower 7 bytes, and avoid this problem.
*/
public static final int LONG_USABLE_BYTES = Long.BYTES - 1;
//The following mapping was determined by brute-forcing -1 Long (all bits 1), and compressing to base45 until it hit zero.
public static final int[] BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION = new int[] {0,2,3,5,6,8,9,11,12};
public static final int NUM_BASE45_DIGITS_PER_LONG = BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION[LONG_USABLE_BYTES];
public static final Map<Integer, Integer> BASE45_TO_BINARY_DIGIT_COUNT_CONVERSION = new HashMap<>();
static {
//Build Reverse Lookup
int len = BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION.length;
for (int x=0; x<len; x++) {
int numB45Digits = BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION[x];
BASE45_TO_BINARY_DIGIT_COUNT_CONVERSION.put(numB45Digits, x);
}
}
public static String encodeToBase45QrPayload(final byte[] inputData) throws IOException {
return encodeToBase45QrPayload(new ByteArrayInputStream(inputData));
}
public static String encodeToBase45QrPayload(final InputStream in) throws IOException {
//Init conversion state vars
final StringBuilder strOut = new StringBuilder();
int data;
long buf = 0;
// Process all input data in chunks of size LONG.BYTES, this allows for economies of scale
// so we can process more digits of arbitrary size before we hit the wall of the binary
// chunk size in a power of 2, and have to transmit a sub-optimal chunk of the "crumbs"
// left over; i.e. the slack space between where the multiples of QR_PAYLOAD_NUMERIC_BASE
// and the powers of 2 don't quite line up.
while(in.available() > 0) {
//Fill buffer
int numBytesStored = 0;
while (numBytesStored < LONG_USABLE_BYTES && in.available() > 0) {
//Read next byte
data = in.read();
//Push byte into buffer
buf = (buf << 8) | data; //8 bits per byte
//Increment
numBytesStored++;
}
//Write out in lower base
final StringBuilder outputChunkBuffer = new StringBuilder();
final int numBase45Digits = BINARY_TO_BASE45_DIGIT_COUNT_CONVERSION[numBytesStored];
int numB45DigitsProcessed = 0;
while(numB45DigitsProcessed < numBase45Digits) {
//Chunk out a digit
final byte digit = (byte) (buf % QR_PAYLOAD_NUMERIC_BASE);
//Drop digit data from buffer
buf = buf / QR_PAYLOAD_NUMERIC_BASE;
//Write Digit
outputChunkBuffer.append(alphaNumReverseIndex[(int) digit]);
//Track output digits
numB45DigitsProcessed++;
}
/*
* The way this code works, the processing output results in a First-In-Last-Out digit
* reversal. So, we need to buffer the chunk output, and feed it to the OutputStream
* backwards to correct this.
*
* We could probably get away with writing the bytes out in inverted order, and then
* flipping them back on the decode side, but just to be safe, I'm always keeping
* them in the proper order.
*/
strOut.append(outputChunkBuffer.reverse().toString());
}
//Return
return strOut.toString();
}
public static byte[] decodeBase45QrPayload(final String inputStr) throws IOException {
//Prep for InputStream
final byte[] buf = inputStr.getBytes();//Use the default encoding (the same encoding that the 'char' primitive uses)
return decodeBase45QrPayload(new ByteArrayInputStream(buf));
}
public static byte[] decodeBase45QrPayload(final InputStream in) throws IOException {
//Init conversion state vars
final ByteArrayOutputStream out = new ByteArrayOutputStream();
int data;
long buf = 0;
int x=0;
// Process all input data in chunks of size LONG.BYTES, this allows for economies of scale
// so we can process more digits of arbitrary size before we hit the wall of the binary
// chunk size in a power of 2, and have to transmit a sub-optimal chunk of the "crumbs"
// left over; i.e. the slack space between where the multiples of QR_PAYLOAD_NUMERIC_BASE
// and the powers of 2 don't quite line up.
while(in.available() > 0) {
//Convert & Fill Buffer
int numB45Digits = 0;
while (numB45Digits < NUM_BASE45_DIGITS_PER_LONG && in.available() > 0) {
//Read in next char
char c = (char) in.read();
//Translate back through lookup table
int digit = ALPHANUMERIC_TABLE[(int) c];
//Shift buffer up one digit to make room
buf *= QR_PAYLOAD_NUMERIC_BASE;
//Append next digit
buf += digit;
//Increment
numB45Digits++;
}
//Write out in higher base
final LinkedList<Byte> outputChunkBuffer = new LinkedList<>();
final int numBytes = BASE45_TO_BINARY_DIGIT_COUNT_CONVERSION.get(numB45Digits);
int numBytesProcessed = 0;
while(numBytesProcessed < numBytes) {
//Chunk out 1 byte
final byte chunk = (byte) buf;
//Shift buffer to next byte
buf = buf >> 8; //8 bits per byte
//Write byte to output
//
//Again, we need to invert the order of the bytes, so as we chunk them off, push
//them onto a FILO stack; inverting their order.
outputChunkBuffer.push(chunk);
//Increment
numBytesProcessed++;
}
//Write chunk buffer to output stream (in reverse order)
while (outputChunkBuffer.size() > 0) {
out.write(outputChunkBuffer.pop());
}
}
//Return
out.flush();
out.close();
return out.toByteArray();
}
}
Here are some tests I ran to verify the code:
#Test
public void stringEncodingTest() throws IOException {
//Init test data
final String testStr = "Some cool input data! !##$%^&*()_+";
//Encode
final String encodedStr = BinaryToBase45Encoder.encodeToBase45QrPayload(testStr.getBytes("UTF-8"));
//Decode
final byte[] decodedBytes = BinaryToBase45Encoder.decodeBase45QrPayload(encodedStr);
final String decodedStr = new String(decodedBytes, "UTF-8");
//Output
final boolean matches = testStr.equals(decodedStr);
assert(matches);
System.out.println("They match!");
}
#Test
public void binaryEncodingAccuracyTest() throws IOException {
//Init test data
final int maxBytes = 10_000;
for (int x=1; x<=maxBytes; x++) {
System.out.print("x: " + x + "\t");
//Encode
final byte[] inputArray = getTestBytes(x);
final String encodedStr = BinaryToBase45Encoder.encodeToBase45QrPayload(inputArray);
//Decode
final byte[] decodedBytes = BinaryToBase45Encoder.decodeBase45QrPayload(encodedStr);
//Output
for (int y=0; y<x; y++) {
assertEquals(inputArray[y], decodedBytes[y]);
}
System.out.println("Passed!");
}
}
#Test
public void binaryEncodingEfficiencyTest() throws IOException, WriterException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
//Init test data
final byte[] inputData = new byte[2048];
new Random().nextBytes(inputData);
//Encode
final String encodedStr = BinaryToBase45Encoder.encodeToBase45QrPayload(inputData);
//Write to QR Code Encoder // Have to use Reflection to force access, since the function is not public.
final BitArray qrCode = new BitArray();
final Method appendAlphanumericBytes = com.google.zxing.qrcode.encoder.Encoder.class.getDeclaredMethod("appendAlphanumericBytes", CharSequence.class, BitArray.class);
appendAlphanumericBytes.setAccessible(true);
appendAlphanumericBytes.invoke(null, encodedStr, qrCode);
//Output
final int origSize = inputData.length;
final int qrSize = qrCode.getSizeInBytes();
System.out.println("Raw Binary Size:\t\t" + origSize + "\nEncoded String Size:\t" + encodedStr.length() + "\nQR Code Alphanum Size:\t" + qrSize);
//Calculate Storage Efficiency Loss
final int delta = origSize - qrSize;
final double efficiency = ((double) delta) / origSize;
System.out.println("Storage Efficiency Loss: " + String.format("%.3f", efficiency * 100) + "%");
}
public static byte[] getTestBytes(int numBytes) {
final Random rand = new Random();
final ByteArrayOutputStream bos = new ByteArrayOutputStream();
for (int x=0; x<numBytes; x++) {
//bos.write(255);// -1 (byte) = 255 (int) = 1111 1111
byte b = (byte) rand.nextInt();
bos.write(b);
}
return bos.toByteArray();
}
I did test mix two PCM audio file.
but don't get true audio file.
I used this example
So, my code:
private void mixSound() throws IOException {
byte[] music1 = null;
music1 = new byte[in1.available()];
music1 = convertStreamToByteArray(in1);
in1.close();
byte[] music2 = null;
music2 = new byte[in2.available()];
music2 = convertStreamToByteArray(in2);
in2.close();
byte[] output = new byte[music1.length];
for (int i = 0; i < output.length; i++) {
samplef1 = music1[i] / 128.0f;
samplef2 = music2[i] / 128.0f;
float mixed = samplef1 + samplef2;
// reduce the volume a bit:
mixed *= 0.8;
// hard clipping
if (mixed > 1.0f) mixed = 1.0f;
if (mixed < -1.0f) mixed = -1.0f;
byte outputSample = (byte) (mixed * 128.0f);
output[i] = outputSample;
} //for loop
save = openFileOutput(filename, Context.MODE_PRIVATE);
save.write(output);
save.flush();
save.close();
}
public byte[] convertStreamToByteArray(InputStream is) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buff = new byte[8000];
int i;
while ((i = is.read(buff, 0, buff.length)) > 0) {
baos.write(buff, 0, i);
}
return baos.toByteArray(); // be sure to close InputStream in calling function
}
2 audio files with bit rate 64000 & sampling rate 16000 GH & sterio
in1 = getResources().openRawResource(R.raw.a_2);
in2 = getResources().openRawResource(R.raw.a_diz_2);
Also try to convert
bytes array to short array -> then calculate-> then convert short to byte using converts methods
like bytes2Shorts(byte[] buf) and shorts2Bytes(short[] s).
But steel have a fail result.
Someone can say me Where is my wrong?
There are a number of issues here and I'll try to address some of them
First, using byte[] suggests that your PCM wave data format is AudioFormat.ENCODING_PCM_8BIT (or it should be this format if it already isn't). This format uses 8-bit (1 byte) unsigned, which means that the sound
samples are stored in the [0, 255] range (not in the [-127, +128] or [-128,+127] range).
This means that the negative values are in the [0, 127] range and the positive samples are in the [128,255] range.
When mixing values, it's best to prevent clipping right from the start so I'd use
byte mixed = (music1[i] + music2[i])/2; //this ensures that mixed remains within the `correct range` for your PCM format
You can also divide your samples by 128 (if you want to convert them to floating point values)
float samplef1 = (((float)music1[i]-127)/128 ; //converting samples to [-1, +1] range -- -1 corresponds a sample value of 0 and +1 to 255
float samplef2 = (((float)music2[i]-127)/128;
float mixed = (samplef1+samplef2)/2;
Note that you now have 2 options to play data(samples) generated in this way. Either, convert floats back to bytes or use the AudioFormat.ENCODING_PCM_FLOAT format.
audio files with bit rate 64000 & sampling rate 16000 GH & sterio
This can't be correct. Typical sampling rates are 4000Hz, 8000Hz, 11000Hz, 16000Hz, 22050Hz or 44100Hz. For bit depths, audio usually uses 8 bits, 16 bits or 32 bits.
For instance, CD quality audio uses 44100Hz, 16bit, stereo format.
My task is convert short[] array to byte[] array, because need send bytes via socket. This is bytes for AudioTrack (Android)
For converting use this post, specifically this and this
This method gives only white noise, when try to convert short to byte array:
val sampleBuffer = decoder.decodeFrame(frameHeader, bitstream) as SampleBuffer
val pcm = sampleBuffer.buffer //pcm is short[] array
byteBuf = ByteBuffer.allocate(pcm.size * 2) // because 1 short = 2 bytes
while (pcm.size > i) {
byteBuf.putShort(pcm[i])
i++
}
auddioTrack.write(byteBuf.array(), 0, byteBuf.limit());
But this convert works fine:
var i = 0
val byteBuf = ByteBuffer.allocate(pcm.size * 2)
val buff = ByteBuffer.allocate(2)
//pcm size equals 2304
while (pcm.size > i) {
// byteBuf.putShort(pcm[i])
byteBuf.put(byteArrayOf((pcm[i].toInt() and 0x00FF).toByte(), ((pcm[i].toInt() and 0xFF00) shr (8)).toByte()))
i++
}
auddioTrack.write(byteBuf.array(), 0, byteBuf.limit());
Why has it happened?
byteBuf.array().size will return the size of the buffer (pcm.size * 2) regardless of whether that many bytes were written into the buffer. You probably want byteBuf.limit() instead.
In java.
I had some file (*.wav) from where I extracted byte[]. After that I converted this to double[] by this code:
for (int i = 0; i < bytesIn.length && idx < buffer.length; i += 2)
{
byte lowByte = bytesIn[i];
byte highByte = bytesIn[i+1];
//Little endian
buffer[idx++] = (lowByte & 0xFF | highByte << 8);
}
Where bytesIn = byte[] of file
and buffer = double[]
After this I did some operation on buffer used fast Fourier transform and inverse. Now after inverse operation from fft I have double[] but I dont know how to get back to byte[].
I found this:
byte[] bytes = new byte[8];
ByteBuffer.wrap(bytes).putDouble(value);
but bytes store different value than I expected. Changed buffer after IFFT is same as original one. Can anyone write how to reverse code from first code block?
I'm making a drum sequencer in Android...
I'm writing to an AudioTrack in MODE_STREAM, so that I can achieve synchronized audio playback with all InputStreams (availible via a list of 'active' InputStreams, activeStreams in the code below)
The audio is always: PCM (WAV), 16bit Stereo 44100 Hz.
Obviously, I can't composite audio in real time on the UI thread, so I'm using an AsyncTask to queue up all the audio buffering.
I got buffered playback working, but when it comes to merging the buffers of two (or more) InputStream's, the internet seems to be in some kind of debate of what to do next. "Convert the byte[] to short[]!", "No, do the bit mixing on-the-fly!", "But if you don't use shorts the byte Endianness is ignored!", "It gets ignored anyway!" - I don't even know any more.
How do I mix the buffer of two or more InputStreams? I don't understand why my current implementation is failing
I've tried like, 4 different StackOverflow solutions to convert the byte[] to short[] so I can add the samples together, but the conversion always instantly crashes Java with some cryptic error message that I can't get my head around. So now I give up. Here's my code implementing one such StackOverflow solution...
protected Long doInBackground(Object ... Object) {
int bytesWritten = 0;
InputStream inputStream;
int si = 0, i = 0;
//The combined buffers. The 'composition'
short[] cBuffer = new short[Synth.AUDIO_BUFFER_SIZE];
//The 'current buffer', the segment of inputStream audio.
byte[] bBuffer = new byte[Synth.AUDIO_BUFFER_SIZE];
//The 'current buffer', converted to short?
short[] sBuffer = new short[Synth.AUDIO_BUFFER_SIZE];
int curStreamNum;
int numStreams = activeStreams.size();
short mix;
//Start with an empty 'composition'
cBuffer = new short[Synth.AUDIO_BUFFER_SIZE];
boolean bufferEmpty = false;
try {
while(true) { // keep going forever, until stopped or paused.
for(curStreamNum = 0;curStreamNum < numStreams;curStreamNum++){
inputStream = activeStreams.get(curStreamNum);
i = inputStream.read(bBuffer);
bufferEmpty = i<=-1;
if(bufferEmpty){
//Input stream buffer was empty. It's out of audio. Close and remove the stream.
inputStream.close();
activeStreams.remove(curStreamNum);
curStreamNum--; numStreams--; continue; // hard continue.
}else{
//Take the now-read buffer, and convert to shorts.
ByteBuffer.wrap(bBuffer).order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().get(sBuffer);
//Take the short buffer, merge into composition buffer.
//TODO: Optimize by making the 'first layer' of the composition the first buffer, on its own.
for(si=0;si<Synth.AUDIO_BUFFER_SIZE;si++){
mix = (short) (sBuffer[si] + cBuffer[si]);
//This part is probably completely wrong too. I'm not up to here yet to evaluate whats needed...
if(mix >= 32767){
mix = 32767;
}else if (mix <= -32768){
mix = -32768;
}
cBuffer[si] = mix;
}
}
}
track.write(sBuffer, 0, i);
//It's always full; full buffer of silence, or of composited audio.
totalBytesWritten += Synth.AUDIO_BUFFER_SIZE;
//.. queueNewInputStreams ..
publishProgress(totalBytesWritten);
if (isCancelled()) break;
}
} catch (IOException e) {e.printStackTrace();}
return Long.valueOf(totalBytesWritten);
}
I'm currently getting a BufferUnderflowException on this line: ByteBuffer.wrap(bBuffer).order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().get(sBuffer);.
How is it possible to have buffer underrun? I'm only converting a byte[] to a short[].
Please help!
I've posted my whole function in the hopes that this more complete code sample and fairly adaptable usage can help other people out there.
(P.S. the byte[] to short[] conversion is followed by some flimsy hard clipping which I'm not even up to debugging yet, but advice there would also be appreciated)
Your solution seems almost good, I see two issues and a potential one:
the length of the short array: it MUST be the half of the byte array, otherwise you get the underflow
the sum of the short must be the average of the shorts and not just the sum, or you'll get just noise
(potential issue) the length of the array you read by InputStream cannot be totally free, since you have to sum 2bytes for every InputStream (then it must be an even array) and you should take care of mono vs. stereo audio files (if stereo you have 2bytes for the left channel and 2bytes for the right channel interleaved)
Here you can find a snippet that I would use to sum of two WAV array (16bit, mono)
Random random = new Random();
int bufferLength = 20;
byte[] is1 = new byte[bufferLength];
byte[] is2 = new byte[bufferLength];
byte[] average = new byte[bufferLength];
random.nextBytes(is1);
random.nextBytes(is2);
short[] shorts1 = new short[bufferLength/2];
ByteBuffer.wrap(is1).order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().get(shorts1);
short[] shorts2 = new short[bufferLength/2];
ByteBuffer.wrap(is2).order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().get(shorts2);
short[] result = new short[bufferLength/2];
for (int i=0; i<result.length; i++) {
result[i] = (short) ((shorts1[i] + shorts2[i])/2);
}
ByteBuffer.wrap(average).order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().put(result);
For a 32bit stereo, the solution could be
Random random = new Random();
int bufferLength = 8 * 50;
byte[] is1 = new byte[bufferLength];
byte[] is2 = new byte[bufferLength];
byte[] average = new byte[bufferLength];
random.nextBytes(is1);
random.nextBytes(is2);
System.out.println(bytesToHex(is1));
System.out.println(bytesToHex(is2));
int[] ints1 = new int[bufferLength/4];
ByteBuffer.wrap(is1).order(ByteOrder.LITTLE_ENDIAN).asIntBuffer().get(ints1);
int[] ints2 = new int[bufferLength/4];
ByteBuffer.wrap(is2).order(ByteOrder.LITTLE_ENDIAN).asIntBuffer().get(ints2);
int[] result = new int[bufferLength/4];
for (int i=0; i<result.length; i++) {
result[i] = ((ints1[i] + ints2[i])/2);
}
ByteBuffer.wrap(average).order(ByteOrder.LITTLE_ENDIAN).asIntBuffer().put(result);