Manually concatenating two wave files

Even though there are libraries and tools to concatenate two canonical wave files, here is how you can do it manually, just in case you need to or are interested.

Take one of the files and add the second files minus the header. Then modify sizes of the file and the actual data part.

You might want to look at the definition of a wave file first.

public byte[] mergeTwoWavFiles(byte[] fileOne, byte[] fileTwo) throws
UnsupportedAudioFileException, IOException {

        long lengthOne = getChunkLength(fileOne);
        long lengthTwo = getChunkLength(fileTwo);

        // result length is wave file lengths minus one header (44)
        byte[] result = new byte[fileOne.length + fileTwo.length - 44];
        System.arraycopy(fileOne, 0, result, 0, fileOne.length);
        System.arraycopy(fileTwo, 44, result, fileOne.length, fileTwo.length - 44);

        // modify ChunkSize
        long combinedChunkSize = lengthOne + lengthTwo;
        byte[] data = longToByteArray(combinedChunkSize);
        result[4] = data[3];
        result[5] = data[2];
        result[6] = data[1];
        result[7] = data[0];

        // modify SubChunkSize
        combinedChunkSize = fileOne.length + fileTwo.length - 88;
        data = longToByteArray(combinedChunkSize);
        result[40] = data[3];
        result[41] = data[2];
        result[42] = data[1];
        result[43] = data[0];

        return result;

     /**
     * get the chunksize length coded in 4 byte
     *
     * @param combinedChunkSize
     * @return
     */
    private byte[] longToByteArray(long combinedChunkSize) {
        byte[] result = new byte[4];
        for (int i = 0; i < 4; ++i) {
            int shift = i << 3; // i * 8
            result[3 - i] = (byte) ((combinedChunkSize & (0xff << shift)) >>> shift);
        }
        return result;
    }

    /**
     * get the length of the wav from its chunksize info
     *
     * @param chunkSize
     * @return
     */
    private long getChunkLength(byte[] chunkSize) {
        long length = 0;
        for (int i = 7; i >= 4; i--) {
            length = (length << 8) + (chunkSize[i] & 0xff);
        }
        return length;
    }

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Nico Heid

I work as a software engineer during the day and sometimes hack a bit in my free time. That currently includes anything from software, system and networks to raspberry pi and hardware. You can find most of my results on this blog.

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