统一通道数和采样率

参考文章 详解如何使用代码进行音频合成
不过，上面给的代码中也有不对的地方（应该是采样点字节数那里），不能全抄。

混音算法

  /**
     * 按音量权值进行混音算法
     */

    private static class WeightAudioMixer extends MultiAudioMixer {
        float weight[];

        public WeightAudioMixer(float[] weight) {
            this.weight = weight;
        }

        @Override
       public byte[] mixRawAudioBytes(byte[][] bMulRoadAudioes) {

            if (bMulRoadAudioes == null || bMulRoadAudioes.length == 0)
                return null;

            byte[] realMixAudio = bMulRoadAudioes[0];

            if (bMulRoadAudioes.length == 1) {
                DLog.i("MultiAudioMixer", "bMulRoadAudioes.length == 1");
                return realMixAudio;
            }

            for (int rw = 0; rw < bMulRoadAudioes.length; ++rw) {
                if (bMulRoadAudioes[rw].length != realMixAudio.length) {
                    Log.e("app", "column of the road of audio + " + rw + " is diffrent.");
                    return null;
                }
            }

            int row = bMulRoadAudioes.length;
            int coloum = realMixAudio.length / 2;
            short[][] sMulRoadAudioes = new short[row][coloum];

            for (int r = 0; r < row; ++r) {
                for (int c = 0; c < coloum; ++c) {
                    sMulRoadAudioes[r][c] = (short) ((bMulRoadAudioes[r][c * 2] & 0xff) | (bMulRoadAudioes[r][c * 2 + 1] & 0xff) << 8);
                    //todo
//                    if(r==0){
//                        sMulRoadAudioes[r][c]=(short) (sMulRoadAudioes[r][c]*firstweight);
//                    }else  if(r==1){
//                        sMulRoadAudioes[r][c]=(short) (sMulRoadAudioes[r][c]*secondweight);
//                    }
                }
            }

            short[] sMixAudio = new short[coloum];
            int mixVal;
            int sr = 0;
            for (int sc = 0; sc < coloum; ++sc) {
                mixVal = 0;
                sr = 0;
                for (; sr < row; ++sr) {
                    //mixVal += sMulRoadAudioes[sr][sc];
                    mixVal += sMulRoadAudioes[sr][sc] * weight[sr];
                    DLog.i("MultiAudioMixer", "sMulRoadAudioes:" + sMulRoadAudioes[sr][sc] + "weight[" + sr + "]:" + weight[sr]);

                }
//                sMixAudio[sc] = (short) (mixVal / row);
                sMixAudio[sc] = (short) (mixVal);
            }

            for (sr = 0; sr < coloum; ++sr) {
                realMixAudio[sr * 2] = (byte) (sMixAudio[sr] & 0x00FF);
                realMixAudio[sr * 2 + 1] = (byte) ((sMixAudio[sr] & 0xFF00) >> 8);
            }

            return realMixAudio;
        }

    }

配合上面那篇文章作者的demo ：https://github.com/CrazyZty/ComposeAudio，基本可以实现背景音乐和视频原声音按音量混合的功能了