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录屏与投屏

问题​

Android 如何实现录屏功能？MediaProjection API 怎么用？

答案​

MediaProjection 录屏流程​

实现步骤​

class ScreenRecordService : Service() {
    private var mediaProjection: MediaProjection? = null
    private var mediaRecorder: MediaRecorder? = null
    private var virtualDisplay: VirtualDisplay? = null

    fun startRecording(resultCode: Int, data: Intent) {
        // 1. 获取 MediaProjection
        val projectionManager = getSystemService(MEDIA_PROJECTION_SERVICE) as MediaProjectionManager
        mediaProjection = projectionManager.getMediaProjection(resultCode, data)

        // 2. 配置 MediaRecorder
        val outputFile = File(getExternalFilesDir(null), "record_${System.currentTimeMillis()}.mp4")
        mediaRecorder = MediaRecorder(this).apply {
            setVideoSource(MediaRecorder.VideoSource.SURFACE)
            setAudioSource(MediaRecorder.AudioSource.MIC)
            setOutputFormat(MediaRecorder.OutputFormat.MPEG_4)
            setVideoEncoder(MediaRecorder.VideoEncoder.H264)
            setAudioEncoder(MediaRecorder.AudioEncoder.AAC)
            setVideoSize(1080, 1920)
            setVideoFrameRate(30)
            setVideoEncodingBitRate(6_000_000)
            setOutputFile(outputFile.absolutePath)
            prepare()
        }

        // 3. 创建 VirtualDisplay，将屏幕镜像到 MediaRecorder 的 Surface
        val metrics = resources.displayMetrics
        virtualDisplay = mediaProjection?.createVirtualDisplay(
            "ScreenRecord",
            1080, 1920, metrics.densityDpi,
            DisplayManager.VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR,
            mediaRecorder?.surface,   // 关键：Surface 来自 MediaRecorder
            null, null
        )

        // 4. 开始录制
        mediaRecorder?.start()
    }

    fun stopRecording() {
        mediaRecorder?.stop()
        mediaRecorder?.release()
        virtualDisplay?.release()
        mediaProjection?.stop()
    }
}
Android 10+ 限制

Android 10 起录屏必须在前台 Service（foregroundServiceType="mediaProjection"）中进行。Android 14 进一步要求每次录屏都必须重新获取用户授权。

截图（单帧捕获）​

// 使用 ImageReader 捕获单帧
val imageReader = ImageReader.newInstance(width, height, PixelFormat.RGBA_8888, 2)

val virtualDisplay = mediaProjection.createVirtualDisplay(
    "Screenshot", width, height, density,
    DisplayManager.VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR,
    imageReader.surface, null, null
)

imageReader.setOnImageAvailableListener({ reader ->
    val image = reader.acquireLatestImage() ?: return@setOnImageAvailableListener
    // Image → Bitmap
    val planes = image.planes
    val buffer = planes[0].buffer
    val bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
    bitmap.copyPixelsFromBuffer(buffer)
    image.close()
    virtualDisplay.release()
}, handler)

常见面试问题​

Q1: 为什么录屏需要前台 Service？​

答案：

录屏涉及用户隐私（屏幕内容可能包含敏感信息）。Android 10 起强制要求 MediaProjection 在前台 Service 中使用，确保用户能通过通知栏看到正在录屏。后台录屏被禁止，进入后台后 MediaProjection 会被自动停止。

Q2: 录屏如何同时录制系统音频？​

答案：

Android 10+ 支持通过 AudioPlaybackCapture API 录制其他应用播放的系统音频。需要在 MediaRecorder 中设置 setAudioSource(MediaRecorder.AudioSource.REMOTE_SUBMIX) 或使用 AudioRecord + AudioPlaybackCaptureConfiguration。但目标应用可以通过 setAllowedCapturePolicy(ALLOW_CAPTURE_BY_NONE) 拒绝被录制。

相关链接​