要在Android中使用FFmpeg合并两个音频文件，可以使用以下代码示例来解决问题。首先，请确保已在项目中正确配置了FFmpeg。

import android.os.AsyncTask;
import android.util.Log;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class MergeAudioTask extends AsyncTask {

    private static final String TAG = "MergeAudioTask";
    private String[] inputPaths;
    private String outputPath;
    private MergeAudioListener listener;

    public MergeAudioTask(String[] inputPaths, String outputPath, MergeAudioListener listener) {
        this.inputPaths = inputPaths;
        this.outputPath = outputPath;
        this.listener = listener;
    }

    @Override
    protected Boolean doInBackground(Void... voids) {
        Process process = null;
        try {
            String cmd = "ffmpeg -i concat:";
            for (String path : inputPaths) {
                cmd += path + "|";
            }
            cmd = cmd.substring(0, cmd.length() - 1); // Remove last pipe character
            cmd += " -c copy " + outputPath;

            process = Runtime.getRuntime().exec(cmd);

            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getErrorStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                Log.e(TAG, "FFmpeg error: " + line);
            }

            int exitCode = process.waitFor();
            return exitCode == 0;

        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        } finally {
            if (process != null) {
                process.destroy();
            }
        }

        return false;
    }

    @Override
    protected void onPostExecute(Boolean success) {
        super.onPostExecute(success);
        if (success) {
            listener.onMergeSuccess(outputPath);
        } else {
            listener.onMergeFailure();
        }
    }

    public interface MergeAudioListener {
        void onMergeSuccess(String mergedFilePath);
        void onMergeFailure();
    }
}

然后，在您的Activity或Fragment中使用以下代码来调用合并音频文件的任务：

String[] inputPaths = {"path/to/audio1.wav", "path/to/audio2.wav"};
String outputPath = "path/to/output.wav";

MergeAudioTask mergeAudioTask = new MergeAudioTask(inputPaths, outputPath, new MergeAudioTask.MergeAudioListener() {
    @Override
    public void onMergeSuccess(String mergedFilePath) {
        // 合并成功
        // 可在此处执行相关操作，例如播放合并后的音频文件
    }

    @Override
    public void onMergeFailure() {
        // 合并失败
        // 可在此处执行相关操作，例如显示错误信息
    }
});
mergeAudioTask.execute();

这样，当任务完成时，将根据成功或失败调用相应的回调方法。