android - MIDI 丢失信息

Question

还有其他人发现 MIDI 消息被丢弃了吗？具体来说，noteOff 之后不会跟随 noteOn，反之亦然。

我尝试过同时使用 Android M 的内置 API、MidiManager 和 https://github.com/kshoji/USB-MIDI-Driver .我已经在两台 Android 设备上试过了。

将同一架钢琴连接到我的计算机不会产生丢失的消息。

不幸的是，钢琴流式传输 MIDI 规范主动感应消息 (0xFE)，我认为这可能无济于事。但令人不安的是，任何消息都被丢弃了。我的下一步是购买一个单独的 MIDI 转 USB 适配器，而不是使用钢琴的 USB 输出。

欢迎任何建议

Answer 1

我找到了 Google 的示例应用程序(官方 API)。他们将 MidiReceiver 类包装在自定义 MidiFramer 类中。我不介意有人解释这段代码如何改变事物，但我的猜测是 Android 将消息分组在一起。这是代码:

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.common.midi;

import android.media.midi.MidiReceiver;
import android.util.Log;

import java.io.IOException;

/**
 * Convert stream of arbitrary MIDI bytes into discrete messages.
 *
 * Parses the incoming bytes and then posts individual messages to the receiver
 * specified in the constructor. Short messages of 1-3 bytes will be complete.
 * System Exclusive messages may be posted in pieces.
 *
 * Resolves Running Status and interleaved System Real-Time messages.
 */
public class MidiFramer extends MidiReceiver {
    private MidiReceiver mReceiver;
    private byte[] mBuffer = new byte[3];
    private int mCount;
    private byte mRunningStatus;
    private int mNeeded;
    private boolean mInSysEx;

    public MidiFramer(MidiReceiver receiver) {
        mReceiver = receiver;
    }

    /*
     * @see android.midi.MidiReceiver#onSend(byte[], int, int, long)
     */
    @Override
    public void onSend(byte[] data, int offset, int count, long timestamp)
            throws IOException {
        int sysExStartOffset = (mInSysEx ? offset : -1);

        for (int i = 0; i < count; i++) {
            final byte currentByte = data[offset];
            final int currentInt = currentByte & 0xFF;
            if (currentInt >= 0x80) { // status byte?
                if (currentInt < 0xF0) { // channel message?
                    mRunningStatus = currentByte;
                    mCount = 1;
                    mNeeded = MidiConstants.getBytesPerMessage(currentByte) - 1;
                } else if (currentInt < 0xF8) { // system common?
                    if (currentInt == 0xF0 /* SysEx Start */) {
                        // Log.i(TAG, "SysEx Start");
                        mInSysEx = true;
                        sysExStartOffset = offset;
                    } else if (currentInt == 0xF7 /* SysEx End */) {
                        // Log.i(TAG, "SysEx End");
                        if (mInSysEx) {
                            mReceiver.send(data, sysExStartOffset,
                                offset - sysExStartOffset + 1, timestamp);
                            mInSysEx = false;
                            sysExStartOffset = -1;
                        }
                    } else {
                        mBuffer[0] = currentByte;
                        mRunningStatus = 0;
                        mCount = 1;
                        mNeeded = MidiConstants.getBytesPerMessage(currentByte) - 1;
                    }
                } else { // real-time?
                    // Single byte message interleaved with other data.
                    if (mInSysEx) {
                        mReceiver.send(data, sysExStartOffset,
                                offset - sysExStartOffset, timestamp);
                        sysExStartOffset = offset + 1;
                    }
                    mReceiver.send(data, offset, 1, timestamp);
                }
            } else { // data byte
                if (!mInSysEx) {
                    mBuffer[mCount++] = currentByte;
                    if (--mNeeded == 0) {
                        if (mRunningStatus != 0) {
                            mBuffer[0] = mRunningStatus;
                        }
                        mReceiver.send(mBuffer, 0, mCount, timestamp);
                        mNeeded = MidiConstants.getBytesPerMessage(mBuffer[0]) - 1;
                        mCount = 1;
                    }
                }
            }
            ++offset;
        }

        // send any accumulatedSysEx data
        if (sysExStartOffset >= 0 && sysExStartOffset < offset) {
            mReceiver.send(data, sysExStartOffset,
                    offset - sysExStartOffset, timestamp);
        }
    }

}