使用LAME，把PCM编码格式的录音文件转换为MP3格式的文件

最近，项目需要把PCM编码的录音文件转为MP3格式。
通过学习，发现可以使用de.sciss.jump3r项目：

        <dependency>
            <groupId>de.sciss</groupId>
            <artifactId>jump3r</artifactId>
            <version>1.0.5</version>
        </dependency>

测试代码：

public class LameTest {
    private static Logger LOG = LoggerFactory.getLogger(LameTest.class);

    @Test
    public void encode() {
        LameEncoder encoder = null;
        try {
            byte[] pcm = Files.readAllBytes(Paths.get("recordFiles/", "20190415_09_0016.wav"));

            int r = ThreadLocalRandom.current().nextInt(1000);
            Path file = Files.createFile(Paths.get("recordFiles/", "file_" + r + ".mp3"));

            AudioFormat format = fileFormat(pcm);
            encoder = new LameEncoder(format);

            byte[] buffer = new byte[encoder.getPCMBufferSize()];

            int bytesToTransfer = Math.min(buffer.length, pcm.length);
            int bytesWritten;
            int currentPcmPosition = 0;
            while (0 < (bytesWritten = encoder.encodeBuffer(pcm, currentPcmPosition, bytesToTransfer, buffer))) {
                currentPcmPosition += bytesToTransfer;
                bytesToTransfer = Math.min(buffer.length, pcm.length - currentPcmPosition);

                Files.write(file, copyOfRange(buffer, 0, bytesWritten), StandardOpenOption.APPEND);
            }

            LOG.info("new file is {}.", file.getFileName());
        } catch (IOException ex) {
            LOG.warn("encode error: {}.", ex);
        } finally {
            encoder.close();
        }
    }

}

wav文件头处理类：

public class WavFileUtil {
    private static Logger LOG = LoggerFactory.getLogger(WavFileUtil.class);

    private static final int HEAD_LENGTH = 12;

    private static final int FORMAT_LENGTH = 24;

    private static boolean isWav(byte[] head) {
        return ("RIFF".equals(new String(head, 0, 4, ISO_8859_1)) &&
                "WAVE".equals(new String(head, 8, 4, ISO_8859_1)));
    }

    private static void fileTooSmall(byte[] file) {
        if (file.length < HEAD_LENGTH + FORMAT_LENGTH) {
            LOG.warn("file is too small, size if {}.", file.length);
            throw new IvcFileException();
        }
    }

    public static int fileSize(byte[] file) {
        fileTooSmall(file);

        byte[] head = copyOfRange(file, 0, HEAD_LENGTH);

        if (isWav(head)) {
            return ByteBuffer.wrap(copyOfRange(head, 4, 8))
                    .order(LITTLE_ENDIAN)
                    .getInt() + 8;
        } else {
            LOG.warn("file format error: expected {}, actual {}.",
                    "[82, 73, 70, 70, *, *, *, *, 87, 65, 86, 69]",
                    head);
            throw new IvcFileException();
        }
    }

    public static AudioFormat fileFormat(byte[] file) {
        fileTooSmall(file);

        byte[] head = copyOfRange(file, 0, HEAD_LENGTH);

        if (isWav(head)) {
            byte[] format = copyOfRange(file, 12, HEAD_LENGTH + FORMAT_LENGTH);
            String chuckID = new String(format, 0, 4, ISO_8859_1);
            int chunkSize = ByteBuffer.wrap(copyOfRange(format, 4, 8))
                    .order(LITTLE_ENDIAN).getInt();
            int audioFmt = ByteBuffer.wrap(copyOfRange(format, 8, 10))
                    .order(LITTLE_ENDIAN).getShort();
            int channels = ByteBuffer.wrap(copyOfRange(format, 10, 12))
                    .order(LITTLE_ENDIAN).getShort();
            int sampleRate = ByteBuffer.wrap(copyOfRange(format, 12, 16))
                    .order(LITTLE_ENDIAN).getInt();
            int byteRate = ByteBuffer.wrap(copyOfRange(format, 16, 20))
                    .order(LITTLE_ENDIAN).getInt();
            int frameSize = ByteBuffer.wrap(copyOfRange(format, 20, 22))
                    .order(LITTLE_ENDIAN).getShort();
            int sampleSizeInBits = ByteBuffer.wrap(copyOfRange(format, 22, 24))
                    .order(LITTLE_ENDIAN).getShort();

            //return new AudioFormat(PCM_SIGNED, sampleRate,
            //        sampleSizeInBits, channels, frameSize, sampleRate, false);
            return new AudioFormat(sampleRate, sampleSizeInBits, channels,
                    false, false);
        } else {
            LOG.warn("file is not a wav.");
            throw new IvcFileException();
        }
    }

}

测试通过，效果还不错。