使用 Bytedeco 将 PCM 编码成 PCmu

首先需要导入 bytedeco 库，然后使用以下代码将 PCM 编码成 PCmu：

import org.bytedeco.javacpp.*;
import static org.bytedeco.javacpp.avcodec.*;
import static org.bytedeco.javacpp.avutil.*;

public class PCMToPCMUConverter {
    public static byte[] convert(byte[] pcmData, int sampleRate, int channels) {
        // 分配 AVCodecContext 和 AVFrame
        AVCodec codec = avcodec_find_encoder(AV_CODEC_ID_PCM_MULAW);
        AVCodecContext codecContext = avcodec_alloc_context3(codec);
        AVFrame frame = av_frame_alloc();

        // 设置 AVCodecContext 参数
        codecContext.sample_fmt(AV_SAMPLE_FMT_S16);
        codecContext.sample_rate(sampleRate);
        codecContext.channels(channels);

        // 打开编码器
        avcodec_open2(codecContext, codec, (AVDictionary) null);

        // 分配输入数据缓冲区
        AVPacket packet = new AVPacket();
        av_init_packet(packet);
        packet.data(null);
        packet.size(0);

        // 分配输出数据缓冲区
        BytePointer outBuffer = new BytePointer(null);
        int outBufferSize = av_samples_get_buffer_size((IntPointer) null, codecContext.channels(),
                1, AV_SAMPLE_FMT_S16, 1);
        av_malloc(outBufferSize).position(0).limit(outBufferSize).get(outBuffer);

        // 将 PCM 数据编码成 PCmu
        byte[] pcmuData = new byte[pcmData.length / 2];
        int pcmuIndex = 0;
        for (int i = 0; i < pcmData.length; i += 2) {
            short pcmSample = (short) (pcmData[i] | (pcmData[i + 1] << 8));
            frame.data(0).putShort(pcmuIndex, pcmSample);
            frame.nb_samples(1);
            frame.format(AV_SAMPLE_FMT_S16);
            frame.channels(channels);
            frame.sample_rate(sampleRate);
            avcodec_send_frame(codecContext, frame);
            while (avcodec_receive_packet(codecContext, packet) == 0) {
                BytePointer data = packet.data();
                int size = packet.size();
                data.position(0).limit(size).get(outBuffer);
                outBuffer.position(0);
                outBuffer.get(pcmuData, pcmuIndex, size);
                pcmuIndex += size;
                av_packet_unref(packet);
            }
        }

        // 清理资源
        avcodec_free_context(codecContext);
        av_frame_free(frame);
        av_packet_unref(packet);
        av_free(outBuffer);

        return pcmuData;
    }
}

使用方法：

byte[] pcmData = ... // PCM 数据
int sampleRate = ... // 采样率
int channels = ... // 声道数
byte[] pcmuData = PCMToPCMUConverter.convert(pcmData, sampleRate, channels); // 将 PCM 编码成 PCmu