麦克风: 启动请求RECORD_AUDIO权限并常驻占用麦克风输入(TV/投影需激活后才输出演唱声)

- 新增 MicActivator: AudioRecord 低开销常驻打开 MIC 并循环读丢弃, 保持输入通道占用 - MainActivity: onCreate 延迟请求麦克风权限(REQUEST_MIC_PERMISSION=12), 授权后激活 - 与 MediaRecorder 录音互斥: startRecording 前 pause, stopRecording 后 resume - onDestroy 释放
2026-09-06 00:39:53 +08:00
parent 9dc0d4b994
commit 197b01f806
2 changed files with 159 additions and 1 deletions
@@ -0,0 +1,127 @@
+package com.local.ktv
+
+import android.media.AudioFormat
+import android.media.AudioRecord
+import android.media.MediaRecorder
+import android.util.Log
+
+/**
+ * 麦克风输入激活器。
+ *
+ * 背景: 电视/投影盒子等设备, 需要某个应用真正打开(占用)麦克风输入通道后,
+ * 系统/音频 HAL 才会把外接麦克风的声音路由到扬声器(供 KTV 演唱)。仅持有
+ * RECORD_AUDIO 权限而不实际录音是不够的。
+ *
+ * 做法: 用一个低开销的 [AudioRecord] 常驻打开麦克风并循环读取丢弃数据,
+ * 保持输入通道占用(不写文件、不对外暴露声音)。与 MediaRecorder 录音互斥:
+ * 开始录音前先 pause, 结束录音后自动 resume。
+ */
+class MicActivator {
+    private val tag = "MicActivator"
+    private var record: AudioRecord? = null
+    private var thread: Thread? = null
+    @Volatile private var running = false
+    @Volatile private var paused = false
+
+    val isActive: Boolean get() = running && !paused
+
+    /** 打开麦克风并保持占用。失败静默(设备无麦克风时不影响 App 使用)。 */
+    @Synchronized
+    fun start() {
+        if (running) return
+        running = true
+        paused = false
+        thread = Thread({ readLoop() }, "mic-activator").also { it.isDaemon = true; it.start() }
+    }
+
+    /** 暂停占用(例如要使用 MediaRecorder 录音时), 保留重开能力。 */
+    @Synchronized
+    fun pause() {
+        if (!running) return
+        paused = true
+        releaseInternal()
+        thread?.interrupt()
+        thread = null
+    }
+
+    /** 恢复占用。 */
+    @Synchronized
+    fun resume() {
+        if (!running) return
+        if (!paused) return
+        paused = false
+        thread = Thread({ readLoop() }, "mic-activator").also { it.isDaemon = true; it.start() }
+    }
+
+    /** 彻底停止(不再自动恢复)。 */
+    @Synchronized
+    fun stop() {
+        running = false
+        paused = false
+        releaseInternal()
+        thread?.interrupt()
+        thread = null
+    }
+
+    private fun readLoop() {
+        var consecutiveFails = 0
+        while (running && !paused) {
+            var recorder: AudioRecord? = null
+            try {
+                val minBuffer = AudioRecord.getMinBufferSize(
+                    16000,
+                    AudioFormat.CHANNEL_IN_MONO,
+                    AudioFormat.ENCODING_PCM_16BIT,
+                )
+                if (minBuffer <= 0) {
+                    // 无可用输入配置(可能无麦克风) → 稍后重试。
+                    sleepQuietly(5000)
+                    continue
+                }
+                recorder = AudioRecord(
+                    MediaRecorder.AudioSource.MIC,
+                    16000,
+                    AudioFormat.CHANNEL_IN_MONO,
+                    AudioFormat.ENCODING_PCM_16BIT,
+                    minBuffer.coerceAtLeast(4096) * 2,
+                )
+                if (recorder.state != AudioRecord.STATE_INITIALIZED) {
+                    sleepQuietly(5000)
+                    continue
+                }
+                record = recorder
+                recorder.startRecording()
+                val buffer = ByteArray(minBuffer.coerceAtLeast(4096))
+                consecutiveFails = 0
+                while (running && !paused) {
+                    // 丢弃读到的数据, 目的仅是让麦克风输入通道保持打开。
+                    val read = recorder.read(buffer, 0, buffer.size)
+                    if (read < 0) {
+                        if (++consecutiveFails > 5) break
+                        sleepQuietly(200)
+                    } else {
+                        consecutiveFails = 0
+                    }
+                }
+            } catch (e: Throwable) {
+                Log.w(tag, "mic keep-alive error: ${e.message}")
+                sleepQuietly(5000)
+            } finally {
+                runCatching { recorder?.stop() }
+                runCatching { recorder?.release() }
+                if (record === recorder) record = null
+            }
+        }
+    }
+
+    private fun releaseInternal() {
+        val r = record
+        record = null
+        runCatching { r?.stop() }
+        runCatching { r?.release() }
+    }
+
+    private fun sleepQuietly(ms: Long) {
+        try { Thread.sleep(ms) } catch (ignored: InterruptedException) { Thread.currentThread().interrupt() }
+    }
+}