android audioflinger 怎样进行音频混合 - 问答

AudioFlinger是Android音频系统的一个关键组件，它负责音频的播放、录制和混合。在Android中，音频混合通常是通过AudioFlinger中的MediaMuxer和MediaCodec类来实现的。以下是一个简单的步骤说明如何进行音频混合：

创建MediaMuxer实例：首先，你需要创建一个MediaMuxer实例，用于写入混合后的音频数据。你需要指定输出文件的格式和路径。例如，创建一个MP3格式的MediaMuxer实例：

MediaMuxer mediaMuxer = new MediaMuxer(outputFilePath, MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);

创建MediaCodec实例：接下来，你需要为每个要混合的音频源创建一个MediaCodec实例。例如，如果你有两个音频源，一个是MP3文件，另一个是AAC文件，你需要为它们分别创建MediaCodec解码器实例：

MediaExtractor mediaExtractor1 = new MediaExtractor();
mediaExtractor1.setDataSource(mp3FilePath);
MediaCodec mediaDecoder1 = MediaCodec.createDecoderByType("audio/mp3");
mediaDecoder1.configure(mediaExtractor1.getTrackInfo(0), null, null, 0);

MediaExtractor mediaExtractor2 = new MediaExtractor();
mediaExtractor2.setDataSource(aacFilePath);
MediaCodec mediaDecoder2 = MediaCodec.createDecoderByType("audio/mp4a-latm");
mediaDecoder2.configure(mediaExtractor2.getTrackInfo(0), null, null, 0);

解码音频数据：使用MediaCodec实例解码音频数据，将其转换为PCM数据：

int bufferSize = 1024;
ByteBuffer[] inputBuffers1 = mediaDecoder1.getInputBuffers();
ByteBuffer[] inputBuffers2 = mediaDecoder2.getInputBuffers();

MediaCodec.BufferInfo bufferInfo1 = new MediaCodec.BufferInfo();
MediaCodec.BufferInfo bufferInfo2 = new MediaCodec.BufferInfo();

int sampleData1, sampleData2;
while (mediaDecoder1.dequeueInputBuffer(-1) >= 0) {
    int inputBufferIndex1 = mediaDecoder1.dequeueInputBuffer(-1);
    sampleData1 = mediaExtractor1.readSampleData(inputBuffers1[inputBufferIndex1], 0);
    if (sampleData1 < 0) {
        mediaDecoder1.queueInputBuffer(inputBufferIndex1, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
    } else {
        mediaDecoder1.queueInputBuffer(inputBufferIndex1, 0, sampleData1, mediaExtractor1.getSampleTime(), 0);
    }
}

while (mediaDecoder2.dequeueInputBuffer(-1) >= 0) {
    int inputBufferIndex2 = mediaDecoder2.dequeueInputBuffer(-1);
    sampleData2 = mediaExtractor2.readSampleData(inputBuffers2[inputBufferIndex2], 0);
    if (sampleData2 < 0) {
        mediaDecoder2.queueInputBuffer(inputBufferIndex2, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
    } else {
        mediaDecoder2.queueInputBuffer(inputBufferIndex2, 0, sampleData2, mediaExtractor2.getSampleTime(), 0);
    }
}

获取PCM数据：解码完成后，从MediaCodec实例中获取PCM数据：

int trackIndex1 = mediaDecoder1.dequeueOutputBuffer(bufferInfo1, 0);
int trackIndex2 = mediaDecoder2.dequeueOutputBuffer(bufferInfo2, 0);

while (trackIndex1 >= 0) {
    ByteBuffer[] outputBuffers1 = mediaDecoder1.getOutputBuffers();
    ByteBuffer outputBuffer1 = outputBuffers1[trackIndex1];
    outputBuffer1.position(bufferInfo1.offset);
    outputBuffer1.limit(bufferInfo1.offset + bufferInfo1.size);
    mediaMuxer.writeSampleData(mediaMuxer.addTrack(mediaExtractor1.getTrackInfo(trackIndex1)), outputBuffer1, bufferInfo1);
    mediaDecoder1.releaseOutputBuffer(trackIndex1, false);
    trackIndex1 = mediaDecoder1.dequeueOutputBuffer(bufferInfo1, 0);
}

while (trackIndex2 >= 0) {
    ByteBuffer[] outputBuffers2 = mediaDecoder2.getOutputBuffers();
    ByteBuffer outputBuffer2 = outputBuffers2[trackIndex2];
    outputBuffer2.position(bufferInfo2.offset);
    outputBuffer2.limit(bufferInfo2.offset + bufferInfo2.size);
    mediaMuxer.writeSampleData(mediaMuxer.addTrack(mediaExtractor2.getTrackInfo(trackIndex2)), outputBuffer2, bufferInfo2);
    mediaDecoder2.releaseOutputBuffer(trackIndex2, false);
    trackIndex2 = mediaDecoder2.dequeueOutputBuffer(bufferInfo2, 0);
}

释放资源：最后，释放MediaMuxer和MediaCodec实例，关闭文件输出流：

mediaMuxer.stop();
mediaMuxer.release();
mediaDecoder1.stop();
mediaDecoder1.release();
mediaDecoder2.stop();
mediaDecoder2.release();

try {
    fos.close();
} catch (IOException e) {
    e.printStackTrace();
}

这样，你就可以使用AudioFlinger进行音频混合了。请注意，这只是一个简化的示例，实际应用中可能需要处理更多的细节，例如错误处理、音频格式转换等。

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