音视频技术 on 伊特瑞特

Android录制本机正在播放的声音

Tue, 18 Feb 2025 18:32:00 +0800

一、声明必要的权限

在 Android 项目中，需要在AndroidManifest.xml文件中添加权限：

	<!--文件存储权限-->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.RECORD_AUDIO" />
    
    <!--高版本录制屏幕需要在前台服务中-->
    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />

二、声明应用允许录制播放的声音

需要在 AndroidManifest.xml文件 application 标签中添加 android:allowAudioPlaybackCapture="true"

三、定义前台服务

AndroidManifest.xml文件中定义前台服务：

    <service
    android:name=".MediaProjectionService"
    android:foregroundServiceType="mediaProjection"
    />

四、开始录制

Activity中定义开始录制的方法:

FFmpeg命令学习

Wed, 25 Dec 2024 20:28:00 +0800

1 概要

ffmpeg 命令格式:

`1`	`ffmpeg [global_options] {[input_file_options] -i input_url} ... {[output_file_options] output_url} ...`

2 说明

ffmpeg是一个通用媒体转换器。它可以读取各种输入 - 包括实时抓取/记录设备 - 过滤并将其转码为多种输出格式。
ffmpeg从选项指定的任意数量的输入“文件”（可以是常规文件、管道、网络流、抓取设备等）读取，并写入 -i任意数量的输出“文件”，这些文件由选项指定一个简单的输出 url。在命令行上找到的任何不能解释为选项的内容都被视为输出 url。

SDP(会话描述协议)介绍

Mon, 23 Dec 2024 19:59:00 +0800

概述

SDP 是一种用于描述多媒体会话的协议，它本身并不用于传输媒体数据，而是提供了有关多媒体会话的信息，如会话名称、时间信息、媒体类型（音频、视频等）、传输地址等。这些信息使得参与会话的各方能够了解会话的细节，从而进行正确的媒体数据传输和处理。

SDP 协议格式

SDP 消息是基于文本的，格式比较灵活，一般由多行文本组成，每行的格式为**<类型>=<值>**。例如：v=0，其中v是类型，表示 SDP 的版本，0是值。

SDP 主要字段解释

SDP示例：

RTSP协议学习

Mon, 23 Dec 2024 18:58:00 +0800

RTSP协议与HTTP协议一样，也是一种文本传输协议。

其请求格式如图:

Android相机预览画面拉伸问题处理

Tue, 12 Nov 2024 17:30:00 +0800

当 Android 相机设置了某个分辨率后预览画面出现变形拉伸，可以通过以下4种方法进行处理：

1. 选择合适的预览分辨率

获取支持的预览尺寸：通过 Camera.Parameters 类的 getSupportedPreviewSizes() 方法获取相机支持的所有预览分辨率列表，然后从中选择一个与屏幕宽高比最接近的分辨率来设置为相机的预览分辨率.
计算最佳预览尺寸：编写方法来计算最佳的预览尺寸，通常是根据屏幕的宽高比与相机支持的预览尺寸的宽高比进行对比，找到差值最小的那个预览尺寸。以下是一个示例方法：

SIP协议学习

Tue, 05 Nov 2024 15:58:00 +0800

SIP协议学习

SIP（Session Initiation Protocol，会话初始协议）是一个应用层的信令控制协议，用于创建、修改和释放一个或多个参与者的会话。以下是关于 SIP 协议的详细介绍：

1.发展历程:

1996 年，出现 SIP 的概念。
1999 年 3 月，IETF（Internet Engineering Task Force，因特网工程任务组）在 RFC2543 中定义了 SIP。
21 世纪初，SIP 得到逐渐推广。随着 LTE 的推广，SIP 成为 LTE 的语音最终解决方案 VoLTE 的主要信令协议，其应用范围从特定环境逐步扩展至主流多媒体通信环境。

2.系统组成:

用户代理（User Agent）：分为用户代理客户端（UAC）和用户代理服务器（UAS）。UAC 负责发起 SIP 请求，UAS 负责接收并响应请求。例如，用户使用的 SIP 电话终端就是一种用户代理，它可以发起呼叫请求（作为 UAC），也可以接收来自其他用户的呼叫请求并进行响应（作为 UAS）。

Android使用MediaMuxer合成MP4

Mon, 04 Nov 2024 16:30:00 +0800

基本概念

MediaMuxer是 Android 提供的一个用于将音频和视频轨道混合（复用）成一个多媒体文件（如 MP4、3GP 等）的工具类。它允许开发者将来自不同来源（例如通过MediaCodec编码后的音频流和视频流）的媒体数据组合在一起，生成一个完整的多媒体文件。

使用步骤

初始化 MediaMuxer

首先，需要创建一个MediaMuxer对象。其构造函数需要传入两个参数，一个是输出文件的路径，另一个是输出文件的格式（例如MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4表示输出为 MP4 格式）。

RTP协议介绍

Tue, 22 Oct 2024 15:59:00 +0800

一、RTP协议概述

RTP（Real-time Transport Protocol），即实时传输协议，在网络传输中占据着至关重要的地位。它是一个为程序指定处理在单点或多点网络服务上传输多媒体数据的方式的英特网传输标准。

RTP 的作用主要是为实时传输音频和视频等多媒体数据提供端到端的网络传输功能。随着互联网的普及和带宽的提升，人们对于实时音视频传输的需求不断增加，RTP 协议应运而生。它通过在数据包中添加时间戳和序列号等信息，保证音视频数据的实时性和顺序性。

Android使用Camera2获取yuv数据

Tue, 08 Oct 2024 14:32:00 +0800

一、声明必要的权限

在 Android 项目中，需要在AndroidManifest.xml文件中添加相机使用权限：

`1`	`<uses-permission android:name = "android.permission.CAMERA"/>`

二、创建管理器

在 Java 或 Kotlin 代码中，创建一个CameraManager实例来管理相机设备：

在java中:

`1`	`CameraManager cameraManager = (CameraManager)getSystemService(Context.CAMERA_SERVICE);`

在Kotlin中:

`1`	`val cameraManager = getSystemService(Context.CAMERA_SERVICE) as CameraManager`

三、获取相机信息

查询相机列表，找到要打开的目标相机:

在java中:

         String[] cameraIds = cameraManager.getCameraIdList();
         String rearCameraId = null;
         for (String id : cameraIds) {
             CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
             Integer facing = characteristics.get(CameraCharacteristics.LENS_FACING);
             if (facing!= null && facing == CameraCharacteristics.LENS_FACING_BACK) {
                 rearCameraId = id;
                 break;
             }
         }

在Kotlin中:

Android MediaRecorder Api解析

Wed, 25 Sep 2024 10:30:00 +0800

android官方文档

一般使用流程

  MediaRecorder recorder = new MediaRecorder();
  recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
  recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
  recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
  recorder.setOutputFile(PATH_NAME);
  recorder.prepare();
  recorder.start();   // 录制已经开始了
  ...
  recorder.stop();
  recorder.reset();   // 重置，这时可以重新设置AudioSource
  recorder.release(); // 释放资源

流程状态图

常见内部类或接口

AudioSource 可选音频源

DEFAULT 默认音频源
MIC 麦克风
VOICE_CALL 打电话
CAMCORDER 相机录像时的音频源
VOICE_COMMUNICATION 语音通话，VoIP，带音频去回声，增益

VideoSource 可选视频源

DEFAULT 系统预设默认
CAMERA 从相机获取视频
SURFACE 从surface中获取

OutputFormat 输出格式

DEFAULT 系统预设默认
THREE_GPP 3GP，视频
MEPG_4 mp4，视频
RAW_AMR
AMR_NB
AMR_WB
AAC_ADIF
AAC_ADTS
OUTPUT_FORMAT_RTP_AVP
MPEG_2_TS
WEBM
HEIF
OGG

AudioEncoder 可选音频编码常量

DEFAULT
AMR_NB
AMR_WB
AAC
HE_AAC
AAC_ELD
VORBIS
OPUS

VideoEncoder 可选视频编码常量

DEFAULT
H263
H264
MPEG_4_SP
VP8
HEVC(H265)
VP9
DOLBY_VISION
AV1

OnErrorListener 错误回调接口

	/*
     * 未指定的MediaRecorder错误
     */
	public static final int MEDIA_RECORDER_ERROR_UNKNOWN=1;
	
	/**
	 * 媒体服务器死亡。在这种情况下，应用程序必须释放MediaRecorder对象并实例化一个新对象 
	 */
	public static final int MEDIA_ERROR_SERVER_DIED = 100;

	public interface OnErrorListener
    {
        /**
         * 在录制时发生错误的时候调用
         *
         * @param mr 遇到错误的MediaRecorder对象
         * @param what  错误类型
         * <ul>
         * <li>{@link #MEDIA_RECORDER_ERROR_UNKNOWN}
         * <li>{@link #MEDIA_ERROR_SERVER_DIED}
         * </ul>
         * @param extra  特定错误类型的错误代码
         */
        void onError(MediaRecorder mr, int what, int extra);
    }

OnInfoListener 录制信息回调接口

	
	//未指定的信息类型
	public static final int MEDIA_RECORDER_INFO_UNKNOWN              = 1;
	
	//达到最大录制时间提示
	public static final int MEDIA_RECORDER_INFO_MAX_DURATION_REACHED = 800;
	
	//达到最大录制文件大小提示
	public static final int MEDIA_RECORDER_INFO_MAX_FILESIZE_REACHED = 801;

	public interface OnInfoListener
    {
        /**
         * 录制过程中提示或警告回调该接口
         *
         * @param mr   触发提示或警告的MediaRecorder
         * @param what 发生的提示或警告类型
         * <ul>
         * <li>{@link #MEDIA_RECORDER_INFO_UNKNOWN}
         * <li>{@link #MEDIA_RECORDER_INFO_MAX_DURATION_REACHED}
         * <li>{@link #MEDIA_RECORDER_INFO_MAX_FILESIZE_REACHED}
         * </ul>
         * @param extra   特定提示或警告类型的代码
         */
        void onInfo(MediaRecorder mr, int what, int extra);
    }

常见方法

视频相关

getSurface():Surface

    /**
     * 获取在使用surface视频源时的surface
     *
     * 只能在prepare方法之后调用. 在调用start方法之前surface中渲染的帧数据将被丢弃
     *
     * @throws IllegalStateException 在调用prepare方法之前，stop方法之后，或者未设置surface视频源调用该方法抛出该异常 
     * @see android.media.MediaRecorder.VideoSource
     */
    public native Surface getSurface();

setInputSurface(Surface):void

    /**
     * 当配置使用SURFACE视频源时，这个方法为录制器设置一个持续更新的surface
     * 只能在prepare方法之前调用
     * @param surface a persistent input surface created by
     *           {@link MediaCodec#createPersistentInputSurface}
     * @throws IllegalStateException if it is called after {@link #prepare} and before
     * {@link #stop}.
     * @throws IllegalArgumentException if the surface was not created by
     *           {@link MediaCodec#createPersistentInputSurface}.
     * @see MediaCodec#createPersistentInputSurface
     * @see MediaRecorder.VideoSource
     */
    public void setInputSurface(@NonNull Surface surface) {
        if (!(surface instanceof MediaCodec.PersistentSurface)) {
            throw new IllegalArgumentException("not a PersistentSurface");
        }
        native_setInputSurface(surface);
    }

setPreviewDisplay(Surface):void

    /**
     * 设置一个surface用来显示当前录制中的视频。需要在prepare方法之前调用
     * Sets a Surface to show a preview of recorded media (video). Calls this
     * before prepare() to make sure that the desirable preview display is
     * set. If {@link #setCamera(Camera)} is used and the surface has been
     * already set to the camera, application do not need to call this. If
     * this is called with non-null surface, the preview surface of the camera
     * will be replaced by the new surface. If this method is called with null
     * surface or not called at all, media recorder will not change the preview
     * surface of the camera.
     *
     * @param sv the Surface to use for the preview
     * @see android.hardware.Camera#setPreviewDisplay(android.view.SurfaceHolder)
     */
    public void setPreviewDisplay(Surface sv) {
        mSurface = sv;
    }

isSystemOnlyAudioSource(int):boolean

    // TODO make AudioSource static (API change) and move this method inside the AudioSource class
    /**
     * @hide
     * @param source An audio source to test
     * @return true if the source is only visible to system components
     */
    public static boolean isSystemOnlyAudioSource(int source) {
        switch(source) {
            case AudioSource.DEFAULT:
            case AudioSource.MIC:
            case AudioSource.VOICE_UPLINK:
            case AudioSource.VOICE_DOWNLINK:
            case AudioSource.VOICE_CALL:
            case AudioSource.CAMCORDER:
            case AudioSource.VOICE_RECOGNITION:
            case AudioSource.VOICE_COMMUNICATION:
            //case REMOTE_SUBMIX:  considered "system" as it requires system permissions
            case AudioSource.UNPROCESSED:
            case AudioSource.VOICE_PERFORMANCE:
                return false;
            default:
                return true;
        }
    }

isValidAudioSource(int):boolean

    /**
     * @hide
     * @param source An audio source to test
     * @return true if the source is a valid one
     */
    public static boolean isValidAudioSource(int source) {
        switch(source) {
            case AudioSource.MIC:
            case AudioSource.VOICE_UPLINK:
            case AudioSource.VOICE_DOWNLINK:
            case AudioSource.VOICE_CALL:
            case AudioSource.CAMCORDER:
            case AudioSource.VOICE_RECOGNITION:
            case AudioSource.VOICE_COMMUNICATION:
            case AudioSource.REMOTE_SUBMIX:
            case AudioSource.UNPROCESSED:
            case AudioSource.VOICE_PERFORMANCE:
            case AudioSource.ECHO_REFERENCE:
            case AudioSource.RADIO_TUNER:
            case AudioSource.HOTWORD:
            case AudioSource.ULTRASOUND:
                return true;
            default:
                return false;
        }
    }

setVideoSource(int):void

    /**
     * Sets the video source to be used for recording. If this method is not
     * called, the output file will not contain an video track. The source needs
     * to be specified before setting recording-parameters or encoders. Call
     * this only before setOutputFormat().
     *
     * @param video_source the video source to use
     * @throws IllegalStateException if it is called after setOutputFormat()
     * @see android.media.MediaRecorder.VideoSource
     */
    public native void setVideoSource(int video_source)
            throws IllegalStateException;

setProfile(CamcorderProfile):void

    /**
     * Uses the settings from a CamcorderProfile object for recording. This method should
     * be called after the video AND audio sources are set, and before setOutputFile().
     * If a time lapse CamcorderProfile is used, audio related source or recording
     * parameters are ignored.
     *
     * @param profile the CamcorderProfile to use
     * @see android.media.CamcorderProfile
     */
    public void setProfile(CamcorderProfile profile) {
        setOutputFormat(profile.fileFormat);
        setVideoFrameRate(profile.videoFrameRate);
        setVideoSize(profile.videoFrameWidth, profile.videoFrameHeight);
        setVideoEncodingBitRate(profile.videoBitRate);
        setVideoEncoder(profile.videoCodec);
        if (profile.quality >= CamcorderProfile.QUALITY_TIME_LAPSE_LOW &&
             profile.quality <= CamcorderProfile.QUALITY_TIME_LAPSE_QVGA) {
            // Nothing needs to be done. Call to setCaptureRate() enables
            // time lapse video recording.
        } else {
            setAudioEncodingBitRate(profile.audioBitRate);
            setAudioChannels(profile.audioChannels);
            setAudioSamplingRate(profile.audioSampleRate);
            setAudioEncoder(profile.audioCodec);
        }
    }

setVideoProfile(VideoProfile):void

    /**
     * Uses the settings from a VideoProfile object for recording.
     * <p>
     * This method should be called after the video AND audio sources are set, and before
     * setOutputFile().
     * <p>
     * This method can be used instead of {@link #setProfile} when using EncoderProfiles.
     *
     * @param profile the VideoProfile to use
     * @see android.media.EncoderProfiles
     * @see android.media.CamcorderProfile#getAll
     */
    public void setVideoProfile(@NonNull EncoderProfiles.VideoProfile profile) {
        setVideoFrameRate(profile.getFrameRate());
        setVideoSize(profile.getWidth(), profile.getHeight());
        setVideoEncodingBitRate(profile.getBitrate());
        setVideoEncoder(profile.getCodec());
        if (profile.getProfile() >= 0) {
            setVideoEncodingProfileLevel(profile.getProfile(), 0 /* level */);
        }
    }

setCaptureRate(double):void

    /**
     * Set video frame capture rate. This can be used to set a different video frame capture
     * rate than the recorded video's playback rate. This method also sets the recording mode
     * to time lapse. In time lapse video recording, only video is recorded. Audio related
     * parameters are ignored when a time lapse recording session starts, if an application
     * sets them.
     *
     * @param fps Rate at which frames should be captured in frames per second.
     * The fps can go as low as desired. However the fastest fps will be limited by the hardware.
     * For resolutions that can be captured by the video camera, the fastest fps can be computed using
     * {@link android.hardware.Camera.Parameters#getPreviewFpsRange(int[])}. For higher
     * resolutions the fastest fps may be more restrictive.
     * Note that the recorder cannot guarantee that frames will be captured at the
     * given rate due to camera/encoder limitations. However it tries to be as close as
     * possible.
     */
    public void setCaptureRate(double fps) {
        // Make sure that time lapse is enabled when this method is called.
        setParameter("time-lapse-enable=1");
        setParameter("time-lapse-fps=" + fps);
    }

setOrientationHint(int):void

    /**
     * Sets the orientation hint for output video playback.
     * This method should be called before prepare(). This method will not
     * trigger the source video frame to rotate during video recording, but to
     * add a composition matrix containing the rotation angle in the output
     * video if the output format is OutputFormat.THREE_GPP or
     * OutputFormat.MPEG_4 so that a video player can choose the proper
     * orientation for playback. Note that some video players may choose
     * to ignore the compostion matrix in a video during playback.
     *
     * @param degrees the angle to be rotated clockwise in degrees.
     * The supported angles are 0, 90, 180, and 270 degrees.
     * @throws IllegalArgumentException if the angle is not supported.
     *
     */
    public void setOrientationHint(int degrees) {
        if (degrees != 0   &&
            degrees != 90  &&
            degrees != 180 &&
            degrees != 270) {
            throw new IllegalArgumentException("Unsupported angle: " + degrees);
        }
        setParameter("video-param-rotation-angle-degrees=" + degrees);
    }

setVideoSize(int,int):void

    /**
     * Sets the width and height of the video to be captured.  Must be called
     * after setVideoSource(). Call this after setOutputFormat() but before
     * prepare().
     *
     * @param width the width of the video to be captured
     * @param height the height of the video to be captured
     * @throws IllegalStateException if it is called after
     * prepare() or before setOutputFormat()
     */
    public native void setVideoSize(int width, int height)
            throws IllegalStateException;

setVideoFrameRate(int):void

    /**
     * Sets the frame rate of the video to be captured.  Must be called
     * after setVideoSource(). Call this after setOutputFormat() but before
     * prepare().
     *
     * @param rate the number of frames per second of video to capture
     * @throws IllegalStateException if it is called after
     * prepare() or before setOutputFormat().
     *
     * NOTE: On some devices that have auto-frame rate, this sets the
     * maximum frame rate, not a constant frame rate. Actual frame rate
     * will vary according to lighting conditions.
     */
    public native void setVideoFrameRate(int rate) throws IllegalStateException;

setVideoEncoder(int):void

    /**
     * Sets the video encoder to be used for recording. If this method is not
     * called, the output file will not contain an video track. Call this after
     * setOutputFormat() and before prepare().
     *
     * @param video_encoder the video encoder to use.
     * @throws IllegalStateException if it is called before
     * setOutputFormat() or after prepare()
     * @see android.media.MediaRecorder.VideoEncoder
     */
    public native void setVideoEncoder(@VideoEncoderValues int video_encoder)
            throws IllegalStateException;

setVideoEncodingBitRate(int):void

    /**
     * Sets the video encoding bit rate for recording. Call this method before prepare().
     * Prepare() may perform additional checks on the parameter to make sure whether the
     * specified bit rate is applicable, and sometimes the passed bitRate will be
     * clipped internally to ensure the video recording can proceed smoothly based on
     * the capabilities of the platform.
     *
     * <p>
     * NB: the actual bitrate and other encoding characteristics may be affected by
     * the minimum quality floor behavior introduced in
     * {@link android.os.Build.VERSION_CODES#S}. More detail on how and where this
     * impacts video encoding can be found in the
     * {@link MediaCodec} page and looking for "quality floor" (near the top of the page).
     *
     * @param bitRate the video encoding bit rate in bits per second.
     */
    public void setVideoEncodingBitRate(int bitRate) {
        if (bitRate <= 0) {
            throw new IllegalArgumentException("Video encoding bit rate is not positive");
        }
        setParameter("video-param-encoding-bitrate=" + bitRate);
    }

setVideoEncodingProfileLevel(int,int):void

    /**
     * Sets the desired video encoding profile and level for recording. The profile and level
     * must be valid for the video encoder set by {@link #setVideoEncoder}. This method can
     * called before or after {@link #setVideoEncoder} but it must be called before {@link #prepare}.
     * {@code prepare()} may perform additional checks on the parameter to make sure that the specified
     * profile and level are applicable, and sometimes the passed profile or level will be
     * discarded due to codec capablity or to ensure the video recording can proceed smoothly
     * based on the capabilities of the platform. <br>Application can also use the
     * {@link MediaCodecInfo.CodecCapabilities#profileLevels} to query applicable combination of profile
     * and level for the corresponding format. Note that the requested profile/level may not be supported by
     * the codec that is actually being used by this MediaRecorder instance.
     * @param profile declared in {@link MediaCodecInfo.CodecProfileLevel}.
     * @param level declared in {@link MediaCodecInfo.CodecProfileLevel}.
     * @throws IllegalArgumentException when an invalid profile or level value is used.
     */
    public void setVideoEncodingProfileLevel(int profile, int level) {
        if (profile < 0)  {
            throw new IllegalArgumentException("Video encoding profile is not positive");
        }
        if (level < 0)  {
            throw new IllegalArgumentException("Video encoding level is not positive");
        }
        setParameter("video-param-encoder-profile=" + profile);
        setParameter("video-param-encoder-level=" + level);
    }

音频相关

setAudioSource(int):void

    /**
     * Sets the audio source to be used for recording. If this method is not
     * called, the output file will not contain an audio track. The source needs
     * to be specified before setting recording-parameters or encoders. Call
     * this only before setOutputFormat().
     *
     * @param audioSource the audio source to use
     * @throws IllegalStateException if it is called after setOutputFormat()
     * @see android.media.MediaRecorder.AudioSource
     */
    public native void setAudioSource(@Source int audioSource)
            throws IllegalStateException;

getAudioSourceMax():int

    /**
     * Gets the maximum value for audio sources.
     * @see android.media.MediaRecorder.AudioSource
     */
    public static final int getAudioSourceMax() {
        return AudioSource.VOICE_PERFORMANCE;
    }

setAudioProfile(AudioProfile):void

    /**
     * Uses the settings from an AudioProfile for recording.
     * <p>
     * This method should be called after the video AND audio sources are set, and before
     * setOutputFile().
     * <p>
     * This method can be used instead of {@link #setProfile} when using EncoderProfiles.
     *
     * @param profile the AudioProfile to use
     * @see android.media.EncoderProfiles
     * @see android.media.CamcorderProfile#getAll
     */
    public void setAudioProfile(@NonNull EncoderProfiles.AudioProfile profile) {
        setAudioEncodingBitRate(profile.getBitrate());
        setAudioChannels(profile.getChannels());
        setAudioSamplingRate(profile.getSampleRate());
        setAudioEncoder(profile.getCodec());
    }

setAudioEncoder(int):void

    /**
     * Sets the audio encoder to be used for recording. If this method is not
     * called, the output file will not contain an audio track. Call this after
     * setOutputFormat() but before prepare().
     *
     * @param audio_encoder the audio encoder to use.
     * @throws IllegalStateException if it is called before
     * setOutputFormat() or after prepare().
     * @see android.media.MediaRecorder.AudioEncoder
     */
    public native void setAudioEncoder(@AudioEncoderValues int audio_encoder)
            throws IllegalStateException;

setAudioSamplingRate(int):void

    /**
     * Sets the audio sampling rate for recording. Call this method before prepare().
     * Prepare() may perform additional checks on the parameter to make sure whether
     * the specified audio sampling rate is applicable. The sampling rate really depends
     * on the format for the audio recording, as well as the capabilities of the platform.
     * For instance, the sampling rate supported by AAC audio coding standard ranges
     * from 8 to 96 kHz, the sampling rate supported by AMRNB is 8kHz, and the sampling
     * rate supported by AMRWB is 16kHz. Please consult with the related audio coding
     * standard for the supported audio sampling rate.
     *
     * @param samplingRate the sampling rate for audio in samples per second.
     */
    public void setAudioSamplingRate(int samplingRate) {
        if (samplingRate <= 0) {
            throw new IllegalArgumentException("Audio sampling rate is not positive");
        }
        setParameter("audio-param-sampling-rate=" + samplingRate);
    }

setAudioChannels(int):void

    /**
     * Sets the number of audio channels for recording. Call this method before prepare().
     * Prepare() may perform additional checks on the parameter to make sure whether the
     * specified number of audio channels are applicable.
     *
     * @param numChannels the number of audio channels. Usually it is either 1 (mono) or 2
     * (stereo).
     */
    public void setAudioChannels(int numChannels) {
        if (numChannels <= 0) {
            throw new IllegalArgumentException("Number of channels is not positive");
        }
        mChannelCount = numChannels;
        setParameter("audio-param-number-of-channels=" + numChannels);
    }

setAudioEncodingBitRate(int):void

    /**
     * Sets the audio encoding bit rate for recording. Call this method before prepare().
     * Prepare() may perform additional checks on the parameter to make sure whether the
     * specified bit rate is applicable, and sometimes the passed bitRate will be clipped
     * internally to ensure the audio recording can proceed smoothly based on the
     * capabilities of the platform.
     *
     * @param bitRate the audio encoding bit rate in bits per second.
     */
    public void setAudioEncodingBitRate(int bitRate) {
        if (bitRate <= 0) {
            throw new IllegalArgumentException("Audio encoding bit rate is not positive");
        }
        setParameter("audio-param-encoding-bitrate=" + bitRate);
    }

setPreferredDevice(AudioDeviceInfo):boolean [AudioRouting]

    /**
     * Specifies an audio device (via an {@link AudioDeviceInfo} object) to route
     * the input from this MediaRecorder.
     * @param deviceInfo The {@link AudioDeviceInfo} specifying the audio source.
     *  If deviceInfo is null, default routing is restored.
     * @return true if succesful, false if the specified {@link AudioDeviceInfo} is non-null and
     * does not correspond to a valid audio input device.
     */
    @Override
    public boolean setPreferredDevice(AudioDeviceInfo deviceInfo) {
        if (deviceInfo != null && !deviceInfo.isSource()) {
            return false;
        }
        int preferredDeviceId = deviceInfo != null ? deviceInfo.getId() : 0;
        boolean status = native_setInputDevice(preferredDeviceId);
        if (status == true) {
            synchronized (this) {
                mPreferredDevice = deviceInfo;
            }
        }
        return status;
    }

getPreferredDevice():AudioDeviceInfo [AudioRouting]

    /**
     * Returns the selected input device specified by {@link #setPreferredDevice}. Note that this
     * is not guaranteed to correspond to the actual device being used for recording.
     */
    @Override
    public AudioDeviceInfo getPreferredDevice() {
        synchronized (this) {
            return mPreferredDevice;
        }
    }

getRoutedDevice():AudioDeviceInfo [AudioRouting]

    /**
     * Returns an {@link AudioDeviceInfo} identifying the current routing of this MediaRecorder
     * Note: The query is only valid if the MediaRecorder is currently recording.
     * If the recorder is not recording, the returned device can be null or correspond to previously
     * selected device when the recorder was last active.
     */
    @Override
    public AudioDeviceInfo getRoutedDevice() {
        int deviceId = native_getRoutedDeviceId();
        if (deviceId == 0) {
            return null;
        }
        return AudioManager.getDeviceForPortId(deviceId, AudioManager.GET_DEVICES_INPUTS);
    }

add/removeOnRoutingChangedListener(OnRoutingChangedListener):void [AudioRouting]

    /**
     * Adds an {@link AudioRouting.OnRoutingChangedListener} to receive notifications of routing
     * changes on this MediaRecorder.
     * @param listener The {@link AudioRouting.OnRoutingChangedListener} interface to receive
     * notifications of rerouting events.
     * @param handler  Specifies the {@link Handler} object for the thread on which to execute
     * the callback. If <code>null</code>, the handler on the main looper will be used.
     */
    @Override
    public void addOnRoutingChangedListener(AudioRouting.OnRoutingChangedListener listener,
                                            Handler handler) {
        synchronized (mRoutingChangeListeners) {
            if (listener != null && !mRoutingChangeListeners.containsKey(listener)) {
                enableNativeRoutingCallbacksLocked(true);
                mRoutingChangeListeners.put(
                        listener, new NativeRoutingEventHandlerDelegate(this, listener,
                                handler != null ? handler : mEventHandler));
            }
        }
    }

    /**
     * Removes an {@link AudioRouting.OnRoutingChangedListener} which has been previously added
     * to receive rerouting notifications.
     * @param listener The previously added {@link AudioRouting.OnRoutingChangedListener} interface
     * to remove.
     */
    @Override
    public void removeOnRoutingChangedListener(AudioRouting.OnRoutingChangedListener listener) {
        synchronized (mRoutingChangeListeners) {
            if (mRoutingChangeListeners.containsKey(listener)) {
                mRoutingChangeListeners.remove(listener);
                enableNativeRoutingCallbacksLocked(false);
            }
        }
    }

getActiveMicrophones():List

    //--------------------------------------------------------------------------
    // Microphone information
    //--------------------
    /**
     * Return A lists of {@link MicrophoneInfo} representing the active microphones.
     * By querying channel mapping for each active microphone, developer can know how
     * the microphone is used by each channels or a capture stream.
     *
     * @return a lists of {@link MicrophoneInfo} representing the active microphones
     * @throws IOException if an error occurs
     */
    public List<MicrophoneInfo> getActiveMicrophones() throws IOException {
        ArrayList<MicrophoneInfo> activeMicrophones = new ArrayList<>();
        int status = native_getActiveMicrophones(activeMicrophones);
        if (status != AudioManager.SUCCESS) {
            if (status != AudioManager.ERROR_INVALID_OPERATION) {
                Log.e(TAG, "getActiveMicrophones failed:" + status);
            }
            Log.i(TAG, "getActiveMicrophones failed, fallback on routed device info");
        }
        AudioManager.setPortIdForMicrophones(activeMicrophones);

        // Use routed device when there is not information returned by hal.
        if (activeMicrophones.size() == 0) {
            AudioDeviceInfo device = getRoutedDevice();
            if (device != null) {
                MicrophoneInfo microphone = AudioManager.microphoneInfoFromAudioDeviceInfo(device);
                ArrayList<Pair<Integer, Integer>> channelMapping = new ArrayList<>();
                for (int i = 0; i < mChannelCount; i++) {
                    channelMapping.add(new Pair(i, MicrophoneInfo.CHANNEL_MAPPING_DIRECT));
                }
                microphone.setChannelMapping(channelMapping);
                activeMicrophones.add(microphone);
            }
        }
        return activeMicrophones;
    }

setPreferredMicrophoneDirection(int):boolean [MicrophoneDirection]

    //--------------------------------------------------------------------------
    // MicrophoneDirection
    //--------------------
    /**
     * Specifies the logical microphone (for processing).
     *
     * @param direction Direction constant.
     * @return true if sucessful.
     */
    public boolean setPreferredMicrophoneDirection(@DirectionMode int direction) {
        return native_setPreferredMicrophoneDirection(direction) == 0;
    }

setPreferredMicrophoneFieldDimension(float):boolean [MicrophoneDirection]

    /**
     * Specifies the zoom factor (i.e. the field dimension) for the selected microphone
     * (for processing). The selected microphone is determined by the use-case for the stream.
     *
     * @param zoom the desired field dimension of microphone capture. Range is from -1 (wide angle),
     * though 0 (no zoom) to 1 (maximum zoom).
     * @return true if sucessful.
     */
    public boolean setPreferredMicrophoneFieldDimension(
                            @FloatRange(from = -1.0, to = 1.0) float zoom) {
        Preconditions.checkArgument(
                zoom >= -1 && zoom <= 1, "Argument must fall between -1 & 1 (inclusive)");
        return native_setPreferredMicrophoneFieldDimension(zoom) == 0;
    }

register/unregisterAudioRecordingCallback([Executor],AudioRecordingCallback):void [AudioRecordingMonitor]

    /**
     * Register a callback to be notified of audio capture changes via a
     * {@link AudioManager.AudioRecordingCallback}. A callback is received when the capture path
     * configuration changes (pre-processing, format, sampling rate...) or capture is
     * silenced/unsilenced by the system.
     * @param executor {@link Executor} to handle the callbacks.
     * @param cb non-null callback to register
     */
    public void registerAudioRecordingCallback(@NonNull @CallbackExecutor Executor executor,
            @NonNull AudioManager.AudioRecordingCallback cb) {
        mRecordingInfoImpl.registerAudioRecordingCallback(executor, cb);
    }

    /**
     * Unregister an audio recording callback previously registered with
     * {@link #registerAudioRecordingCallback(Executor, AudioManager.AudioRecordingCallback)}.
     * @param cb non-null callback to unregister
     */
    public void unregisterAudioRecordingCallback(@NonNull AudioManager.AudioRecordingCallback cb) {
        mRecordingInfoImpl.unregisterAudioRecordingCallback(cb);
    }

getActiveRecordingConfiguration():AudioRecordingConfiguration [AudioRecordingMonitor]

    /**
     * Returns the current active audio recording for this audio recorder.
     * @return a valid {@link AudioRecordingConfiguration} if this recorder is active
     * or null otherwise.
     * @see AudioRecordingConfiguration
     */
    public @Nullable AudioRecordingConfiguration getActiveRecordingConfiguration() {
        return mRecordingInfoImpl.getActiveRecordingConfiguration();
    }

其他

setPrivacySensitive(boolean):void

    /**
     * Indicates that this capture request is privacy sensitive and that
     * any concurrent capture is not permitted.
     * <p>
     * The default is not privacy sensitive except when the audio source set with
     * {@link #setAudioSource(int)} is {@link AudioSource#VOICE_COMMUNICATION} or
     * {@link AudioSource#CAMCORDER}.
     * <p>
     * Always takes precedence over default from audio source when set explicitly.
     * <p>
     * Using this API is only permitted when the audio source is one of:
     * <ul>
     * <li>{@link AudioSource#MIC}</li>
     * <li>{@link AudioSource#CAMCORDER}</li>
     * <li>{@link AudioSource#VOICE_RECOGNITION}</li>
     * <li>{@link AudioSource#VOICE_COMMUNICATION}</li>
     * <li>{@link AudioSource#UNPROCESSED}</li>
     * <li>{@link AudioSource#VOICE_PERFORMANCE}</li>
     * </ul>
     * Invoking {@link #prepare()} will throw an IOException if this
     * condition is not met.
     * <p>
     * Must be called after {@link #setAudioSource(int)} and before {@link #setOutputFormat(int)}.
     * @param privacySensitive True if capture from this MediaRecorder must be marked as privacy
     * sensitive, false otherwise.
     * @throws IllegalStateException if called before {@link #setAudioSource(int)}
     * or after {@link #setOutputFormat(int)}
     */
    public native void setPrivacySensitive(boolean privacySensitive);

isPrivacySensitive():boolean

    /**
     * Returns whether this MediaRecorder is marked as privacy sensitive or not with
     * regard to audio capture.
     * <p>
     * See {@link #setPrivacySensitive(boolean)}
     * <p>
     * @return true if privacy sensitive, false otherwise
     */
    public native boolean isPrivacySensitive();

setLocation(float,float):void

    /**
     * Set and store the geodata (latitude and longitude) in the output file.
     * This method should be called before prepare(). The geodata is
     * stored in udta box if the output format is OutputFormat.THREE_GPP
     * or OutputFormat.MPEG_4, and is ignored for other output formats.
     * The geodata is stored according to ISO-6709 standard.
     *
     * @param latitude latitude in degrees. Its value must be in the
     * range [-90, 90].
     * @param longitude longitude in degrees. Its value must be in the
     * range [-180, 180].
     *
     * @throws IllegalArgumentException if the given latitude or
     * longitude is out of range.
     *
     */
    public void setLocation(float latitude, float longitude) {
        int latitudex10000  = (int) (latitude * 10000 + 0.5);
        int longitudex10000 = (int) (longitude * 10000 + 0.5);

        if (latitudex10000 > 900000 || latitudex10000 < -900000) {
            String msg = "Latitude: " + latitude + " out of range.";
            throw new IllegalArgumentException(msg);
        }
        if (longitudex10000 > 1800000 || longitudex10000 < -1800000) {
            String msg = "Longitude: " + longitude + " out of range";
            throw new IllegalArgumentException(msg);
        }

        setParameter("param-geotag-latitude=" + latitudex10000);
        setParameter("param-geotag-longitude=" + longitudex10000);
    }

setOutputFormat(int):void

    /**
     * Sets the format of the output file produced during recording. Call this
     * after setAudioSource()/setVideoSource() but before prepare().
     *
     * <p>It is recommended to always use 3GP format when using the H.263
     * video encoder and AMR audio encoder. Using an MPEG-4 container format
     * may confuse some desktop players.</p>
     *
     * @param output_format the output format to use. The output format
     * needs to be specified before setting recording-parameters or encoders.
     * @throws IllegalStateException if it is called after prepare() or before
     * setAudioSource()/setVideoSource().
     * @see android.media.MediaRecorder.OutputFormat
     */
    public native void setOutputFormat(@OutputFormatValues int output_format)
            throws IllegalStateException;

setMaxDuration(int):void

    /**
     * Sets the maximum duration (in ms) of the recording session.
     * Call this after setOutputFormat() but before prepare().
     * After recording reaches the specified duration, a notification
     * will be sent to the {@link android.media.MediaRecorder.OnInfoListener}
     * with a "what" code of {@link #MEDIA_RECORDER_INFO_MAX_DURATION_REACHED}
     * and recording will be stopped. Stopping happens asynchronously, there
     * is no guarantee that the recorder will have stopped by the time the
     * listener is notified.
     *
     * <p>When using MPEG-4 container ({@link #setOutputFormat(int)} with
     * {@link OutputFormat#MPEG_4}), it is recommended to set maximum duration that fits the use
     * case. Setting a larger than required duration may result in a larger than needed output file
     * because of space reserved for MOOV box expecting large movie data in this recording session.
     *  Unused space of MOOV box is turned into FREE box in the output file.</p>
     *
     * @param max_duration_ms the maximum duration in ms (if zero or negative, disables the duration limit)
     *
     */
    public native void setMaxDuration(int max_duration_ms) throws IllegalArgumentException;

setMaxFileSize(long):void

    /**
     * Sets the maximum filesize (in bytes) of the recording session.
     * Call this after setOutputFormat() but before prepare().
     * After recording reaches the specified filesize, a notification
     * will be sent to the {@link android.media.MediaRecorder.OnInfoListener}
     * with a "what" code of {@link #MEDIA_RECORDER_INFO_MAX_FILESIZE_REACHED}
     * and recording will be stopped. Stopping happens asynchronously, there
     * is no guarantee that the recorder will have stopped by the time the
     * listener is notified.
     *
     * <p>When using MPEG-4 container ({@link #setOutputFormat(int)} with
     * {@link OutputFormat#MPEG_4}), it is recommended to set maximum filesize that fits the use
     * case. Setting a larger than required filesize may result in a larger than needed output file
     * because of space reserved for MOOV box expecting large movie data in this recording session.
     * Unused space of MOOV box is turned into FREE box in the output file.</p>
     *
     * @param max_filesize_bytes the maximum filesize in bytes (if zero or negative, disables the limit)
     *
     */
    public native void setMaxFileSize(long max_filesize_bytes) throws IllegalArgumentException;

setOutputFile(FileDescriptor/FIle):void

    /**
     * Pass in the file descriptor of the file to be written. Call this after
     * setOutputFormat() but before prepare().
     *
     * @param fd an open file descriptor to be written into.
     * @throws IllegalStateException if it is called before
     * setOutputFormat() or after prepare()
     */
    public void setOutputFile(FileDescriptor fd) throws IllegalStateException
    {
        mPath = null;
        mFile = null;
        mFd = fd;
    }

    /**
     * Pass in the file object to be written. Call this after setOutputFormat() but before prepare().
     * File should be seekable. After setting the next output file, application should not use the
     * file until {@link #stop}. Application is responsible for cleaning up unused files after
     * {@link #stop} is called.
     *
     * @param file the file object to be written into.
     */
    public void setOutputFile(File file)
    {
        mPath = null;
        mFd = null;
        mFile = file;
    }

setNextOutputFile(File):void

    /**
     * Sets the next output file descriptor to be used when the maximum filesize is reached
     * on the prior output {@link #setOutputFile} or {@link #setNextOutputFile}). File descriptor
     * must be seekable and writable. After setting the next output file, application should not
     * use the file referenced by this file descriptor until {@link #stop}. It is the application's
     * responsibility to close the file descriptor. It is safe to do so as soon as this call returns.
     * Application must call this after receiving on the
     * {@link android.media.MediaRecorder.OnInfoListener} a "what" code of
     * {@link #MEDIA_RECORDER_INFO_MAX_FILESIZE_APPROACHING} and before receiving a "what" code of
     * {@link #MEDIA_RECORDER_INFO_MAX_FILESIZE_REACHED}. The file is not used until switching to
     * that output. Application will receive{@link #MEDIA_RECORDER_INFO_NEXT_OUTPUT_FILE_STARTED}
     * when the next output file is used. Application will not be able to set a new output file if
     * the previous one has not been used. Application is responsible for cleaning up unused files
     * after {@link #stop} is called.
     *
     * @param fd an open file descriptor to be written into.
     * @throws IllegalStateException if it is called before prepare().
     * @throws IOException if setNextOutputFile fails otherwise.
     */
    public void setNextOutputFile(FileDescriptor fd) throws IOException
    {
        _setNextOutputFile(fd);
    }

prepare():void

    /**
     * Prepares the recorder to begin capturing and encoding data. This method
     * must be called after setting up the desired audio and video sources,
     * encoders, file format, etc., but before start().
     *
     * @throws IllegalStateException if it is called after
     * start() or before setOutputFormat().
     * @throws IOException if prepare fails otherwise.
     */
    public void prepare() throws IllegalStateException, IOException
    {
        if (mPath != null) {
            RandomAccessFile file = new RandomAccessFile(mPath, "rw");
            try {
                _setOutputFile(file.getFD());
            } finally {
                file.close();
            }
        } else if (mFd != null) {
            _setOutputFile(mFd);
        } else if (mFile != null) {
            RandomAccessFile file = new RandomAccessFile(mFile, "rw");
            try {
                _setOutputFile(file.getFD());
            } finally {
                file.close();
            }
        } else {
            throw new IOException("No valid output file");
        }

        _prepare();
    }

start():void

    /**
     * Begins capturing and encoding data to the file specified with
     * setOutputFile(). Call this after prepare().
     *
     * <p>Since API level 13, if applications set a camera via
     * {@link #setCamera(Camera)}, the apps can use the camera after this method
     * call. The apps do not need to lock the camera again. However, if this
     * method fails, the apps should still lock the camera back. The apps should
     * not start another recording session during recording.
     *
     * @throws IllegalStateException if it is called before
     * prepare() or when the camera is already in use by another app.
     */
    public native void start() throws IllegalStateException;

stop():void

    /**
     * Stops recording. Call this after start(). Once recording is stopped,
     * you will have to configure it again as if it has just been constructed.
     * Note that a RuntimeException is intentionally thrown to the
     * application, if no valid audio/video data has been received when stop()
     * is called. This happens if stop() is called immediately after
     * start(). The failure lets the application take action accordingly to
     * clean up the output file (delete the output file, for instance), since
     * the output file is not properly constructed when this happens.
     *
     * @throws IllegalStateException if it is called before start()
     */
    public native void stop() throws IllegalStateException;

pause():void

    /**
     * Pauses recording. Call this after start(). You may resume recording
     * with resume() without reconfiguration, as opposed to stop(). It does
     * nothing if the recording is already paused.
     *
     * When the recording is paused and resumed, the resulting output would
     * be as if nothing happend during paused period, immediately switching
     * to the resumed scene.
     *
     * @throws IllegalStateException if it is called before start() or after
     * stop()
     */
    public native void pause() throws IllegalStateException;

resume():void

    /**
     * Resumes recording. Call this after start(). It does nothing if the
     * recording is not paused.
     *
     * @throws IllegalStateException if it is called before start() or after
     * stop()
     * @see android.media.MediaRecorder#pause
     */
    public native void resume() throws IllegalStateException;

reset():void

    /**
     * Restarts the MediaRecorder to its idle state. After calling
     * this method, you will have to configure it again as if it had just been
     * constructed.
     */
    public void reset() {
        native_reset();

        // make sure none of the listeners get called anymore
        mEventHandler.removeCallbacksAndMessages(null);
    }

getMaxAmplitude():int

    /**
     * Returns the maximum absolute amplitude that was sampled since the last
     * call to this method. Call this only after the setAudioSource().
     *
     * @return the maximum absolute amplitude measured since the last call, or
     * 0 when called for the first time
     * @throws IllegalStateException if it is called before
     * the audio source has been set.
     */
    public native int getMaxAmplitude() throws IllegalStateException;

setOnErrorListener(OnErrorListener):void

    /**
     * Register a callback to be invoked when an error occurs while
     * recording.
     *
     * @param l the callback that will be run
     */
    public void setOnErrorListener(OnErrorListener l)
    {
        mOnErrorListener = l;
    }

setOnInfoListener(OnInfoListener):void

    /**
     * Register a callback to be invoked when an informational event occurs while
     * recording.
     *
     * @param listener the callback that will be run
     */
    public void setOnInfoListener(OnInfoListener listener)
    {
        mOnInfoListener = listener;
    }

getPortedId():int

    //---------------------------------------------------------
    // Implementation of AudioRecordingMonitorClient interface
    //--------------------
    /**
     * @hide
     */
    public int getPortId() {
        if (mNativeContext == 0) {
            return 0;
        }
        return native_getPortId();
    }

release():void

    /**
     * Releases resources associated with this MediaRecorder object.
     * It is good practice to call this method when you're done
     * using the MediaRecorder. In particular, whenever an Activity
     * of an application is paused (its onPause() method is called),
     * or stopped (its onStop() method is called), this method should be
     * invoked to release the MediaRecorder object, unless the application
     * has a special need to keep the object around. In addition to
     * unnecessary resources (such as memory and instances of codecs)
     * being held, failure to call this method immediately if a
     * MediaRecorder object is no longer needed may also lead to
     * continuous battery consumption for mobile devices, and recording
     * failure for other applications if no multiple instances of the
     * same codec are supported on a device. Even if multiple instances
     * of the same codec are supported, some performance degradation
     * may be expected when unnecessary multiple instances are used
     * at the same time.
     */
    public native void release();

Android使用AudioRecord录制AAC音频

Wed, 25 Sep 2024 10:30:00 +0800

在 Android 中使用 AudioRecord 录制 AAC 音频可以按照以下步骤进行：

一、添加权限

在 AndroidManifest.xml 文件中添加录音权限：

<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" /> <!--android 11 以上-->

二、初始化参数

确定音频输入源，通常可以使用 MediaRecorder.AudioSource.MIC（麦克风）。
选择音频采样率，常见的有 44100Hz、48000Hz 等。
确定音频通道配置，如单声道（AudioFormat.CHANNEL_IN_MONO）或立体声（AudioFormat.CHANNEL_IN_STEREO）。
选择音频编码格式，这里需要选择支持 AAC 编码的格式，如 AudioFormat.ENCODING_PCM_16BIT，后续再进行 AAC 编码转换。
计算最小缓冲区大小，可以使用 AudioRecord.getMinBufferSize() 方法来获取满足上述参数要求的最小缓冲区大小。

三、初始化 AudioRecord 对象

Android使用Camera1获取yuv数据

Wed, 25 Sep 2024 10:30:00 +0800

一、设置权限

在 AndroidManifest.xml 文件中添加相机权限和存储权限（如果需要保存数据的话）：

1
2

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

二、布局设置

在布局文件中添加一个 SurfaceView 用于显示相机预览：

<SurfaceView
    android:id="@+id/surfaceView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

三、初始化相机

在 Activity 或 Fragment 中，获取 SurfaceView 实例并设置其 holder：

   SurfaceView surfaceView = findViewById(R.id.surfaceView);
   SurfaceHolder surfaceHolder = surfaceView.getHolder();
   surfaceHolder.addCallback(new SurfaceHolder.Callback() {
       @Override
       public void surfaceCreated(SurfaceHolder holder) {
           // Surface 创建时初始化相机
           initCamera();
       }

       @Override
       public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
           // Surface 尺寸改变时
       }

       @Override
       public void surfaceDestroyed(SurfaceHolder holder) {
           // Surface 销毁时释放相机资源
           releaseCamera();
       }
   });

初始化相机的方法：

Android使用MediaRecorder录制aac音频

Wed, 25 Sep 2024 10:30:00 +0800

在 Android 中使用MediaRecorder录制 AAC 音频可以按照以下步骤进行：

一、添加权限

在 AndroidManifest.xml 文件中添加以下权限：

1
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<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

二、初始化 MediaRecorder

在你的 Activity 或 Fragment 中初始化MediaRecorder：

`1`	`MediaRecorder mediaRecorder = new MediaRecorder();`

三、设置音频源、输出格式和编码器

mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC); //设置音频源
mediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.AAC_ADTS); //设置输出格式
mediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC); //音频编码格式为aac
mediaRecorder.setAudioSamplingRate(8000);//设置采样率

四、设置输出文件路径

`1`	`mediaRecorder.setOutputFile("/path/to/your/output/file.aac");`

这里的文件路径可以根据你的需求进行设置，可以是内部存储路径或外部存储路径。

视频百科

Wed, 25 Sep 2024 10:30:00 +0800

视频的基本构成
- 图像帧：视频是由一系列连续的图像帧组成，每一张图像称为一帧。这些帧按顺序快速播放，利用人眼的视觉暂留效应，使人感觉像是在观看连续的动态画面。例如，在一个 30fps（帧每秒）的视频中，每秒钟就会有 30 张不同的图像帧依次展示。
- 像素：像素是图像的基本单元，一个个像素组合在一起构成了图像帧。屏幕上的每个像素点都由红（R）、绿（G）、蓝（B）三种颜色的光组成，通过不同强度的组合，可以呈现出各种丰富的色彩。像素的数量和分布决定了图像的清晰度和分辨率

音频百科

Wed, 25 Sep 2024 10:30:00 +0800

此处所讲的音频(Audio) 是指自然界的声音，包括人声等，通过技术手段在计算机中存储或表现的一种形式

自然界的声音都是模拟信号，是一种波，计算机通过采样器(一般是麦克风等设备)捕获到声音的特征并用计算机能识别的数字信号来表示

音频PCM编码

一般音频采集是采用PCM（Pulse Code Modulation）脉冲编码调制进行模拟信号到数字信号的转换。是将模拟信号每隔一定时间进行取样，使其离散化，同时将抽样值按分层单位四舍五入取整量化，同时将抽样值按一组二进制码来表示抽样脉冲的幅值。