android mp3转pcm

在 Android 平台上，可以使用 Android 自带的 MediaCodec 类来完成 MP3 转 PCM 的操作。下面是一个简单的示例代码：

import android.media.MediaCodec;
import android.media.MediaExtractor;
import android.media.MediaFormat;

import java.io.FileOutputStream;
import java.nio.ByteBuffer;

public class Mp3ToPcmConverter {

    public static void convert(String mp3FilePath, String pcmFilePath) throws Exception {
        MediaExtractor extractor = new MediaExtractor();
        extractor.setDataSource(mp3FilePath);

        int audioTrackIndex = -1;
        int trackCount = extractor.getTrackCount();
        for (int i = 0; i < trackCount; i++) {
            MediaFormat format = extractor.getTrackFormat(i);
            String mime = format.getString(MediaFormat.KEY_MIME);
            if (mime.startsWith("audio/")) {
                audioTrackIndex = i;
                break;
            }
        }

        if (audioTrackIndex == -1) {
            throw new IllegalStateException("No audio track found in " + mp3FilePath);
        }

        extractor.selectTrack(audioTrackIndex);
        MediaFormat audioFormat = extractor.getTrackFormat(audioTrackIndex);

        MediaCodec codec = MediaCodec.createDecoderByType(audioFormat.getString(MediaFormat.KEY_MIME));
        codec.configure(audioFormat, null, null, 0);
        codec.start();

        ByteBuffer[] codecInputBuffers = codec.getInputBuffers();
        ByteBuffer[] codecOutputBuffers = codec.getOutputBuffers();

        FileOutputStream fos = new FileOutputStream(pcmFilePath);

        boolean inputDone = false;
        boolean outputDone = false;
        long presentationTimeUs = 0;

        while (!outputDone) {
            if (!inputDone) {
                int inputBufferIndex = codec.dequeueInputBuffer(10000);
                if (inputBufferIndex >= 0) {
                    ByteBuffer inputBuffer = codecInputBuffers[inputBufferIndex];
                    int sampleSize = extractor.readSampleData(inputBuffer, 0);
                    if (sampleSize < 0) {
                        codec.queueInputBuffer(inputBufferIndex, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
                        inputDone = true;
                    } else {
                        codec.queueInputBuffer(inputBufferIndex, 0, sampleSize, presentationTimeUs, 0);
                        presentationTimeUs = extractor.getSampleTime();
                        extractor.advance();
                    }
                }
            }

            int outputBufferIndex = codec.dequeueOutputBuffer(new MediaCodec.BufferInfo(), 10000);
            if (outputBufferIndex >= 0) {
                ByteBuffer outputBuffer = codecOutputBuffers[outputBufferIndex];
                outputBuffer.position(0);
                byte[] pcmData = new byte[outputBuffer.remaining()];
                outputBuffer.get(pcmData);
                fos.write(pcmData);
                codec.releaseOutputBuffer(outputBufferIndex, false);
                if ((outputBufferIndex & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
                    outputDone = true;
                }
            } else if (outputBufferIndex == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
                audioFormat = codec.getOutputFormat();
            }
        }

        fos.flush();
        fos.close();
        codec.stop();
        codec.release();
        extractor.release();
    }
}

使用方法：

try {
    Mp3ToPcmConverter.convert("/sdcard/test.mp3", "/sdcard/test.pcm");
} catch (Exception e) {
    e.printStackTrace();
}

其中 `/sdcard/test.mp3` 是输入的 MP3 文件路径，`/sdcard/test.pcm` 是输出的 PCM 文件路径。注意，此代码仅供参考，实际使用时可能需要根据自己的需求进行修改。