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前言：

目前随着手机分辨率越来越高，几十秒的视频动不动就几百兆，为了减少传输大小，就需要对原有视频进行压缩，那么在鸿蒙中，如果不引入三方组件如何实现视频压缩呢。下面将介绍一种方法，使用鸿蒙的媒体库实现视频压缩

一、使用AVTranscoder实现视频压缩

主要步骤如下：

（1）设置压缩参数，比如设置比特率，通过设置比特率可以控制压缩后的视频大小，比如一个100M的视频，时长为30s，如果想要压缩到10M以内，则设置比特率为 10 * 8 * 1024 * 1024 / 30 约等于2500000，为了去除音频大小的影响，我们可以再乘以0.8，差不多为2000000

（2）设置压缩过程的回调函数，监听视频压缩是否成功

（3）设置待压缩的视频句柄，设置输出视频的路径句柄

二、下面展示从相册中选中视频，并压缩到10M以内的完整示例：

1、从相册中选择视频代码：

import { photoAccessHelper } from "@kit.MediaLibraryKit";export class FileUtil {static async selectVideo() {const photoViewPicker = new photoAccessHelper.PhotoViewPicker()const photoSelectOptions = new photoAccessHelper.PhotoSelectOptions()photoSelectOptions.MIMEType = photoAccessHelper.PhotoViewMIMETypes.VIDEO_TYPEphotoSelectOptions.maxSelectNumber = 1let result = await photoViewPicker.select(photoSelectOptions)let uris = result.photoUris || []if (uris.length) {return uris[0]}return ""}
}

2、使用AVTranscoder压缩视频，并将压缩后的视频存入应用沙箱

import { media } from '@kit.MediaKit';
import { BusinessError } from '@kit.BasicServicesKit';
import { common } from '@kit.AbilityKit';
import { FileUtil } from './FileUtil';
import {fileIo as fs} from '@kit.CoreFileKit'export class AVTranscoderDemo {private avTranscoder: media.AVTranscoder | undefined = undefined;private avConfig: media.AVTranscoderConfig = {audioCodec: media.CodecMimeType.AUDIO_AAC, // 音频编码格式。fileFormat: media.ContainerFormatType.CFT_MPEG_4, // 封装格式。videoBitrate: 2000000, // 视频比特率。videoCodec: media.CodecMimeType.VIDEO_AVC, // 视频编码格式。};// 注册avTranscoder回调函数。setAVTranscoderCallback() {if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {if (this.avTranscoder != undefined) {// 转码完成回调函数。this.avTranscoder.on('complete', async () => {console.log(`AVTranscoder is completed`);await this.releaseTranscoderingProcess();});// 错误上报回调函数。this.avTranscoder.on('error', (err: BusinessError) => {console.error(`AVTranscoder failed, code is ${err.code}, message is ${err.message}`);});}}}// 开始转码对应的流程。async startTranscoderingProcess() {if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {if (this.avTranscoder != undefined) {await this.avTranscoder.release();this.avTranscoder = undefined;}// 1.创建转码实例。this.avTranscoder = await media.createAVTranscoder();this.setAVTranscoderCallback();// 2.从相册选取视频let viedoInput = await FileUtil.selectVideo();let fileDescriptor = await fs.open(viedoInput, fs.OpenMode.READ_ONLY)this.avTranscoder.fdSrc = fileDescriptor;// 3、指定压缩后的视频路径let context = getContext(this) as common.UIAbilityContextlet targetPath = context?.filesDir + '/' + new Date().getTime()+'test.mp4'let targetFile = await fs.open(targetPath,fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE)this.avTranscoder.fdDst = targetFile.fd;// 3.配置转码参数完成准备工作。await this.avTranscoder.prepare(this.avConfig);// 4.开始转码。await this.avTranscoder.start();}}// 暂停转码对应的流程。async pauseTranscoderingProcess() {if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {if (this.avTranscoder != undefined) { // 仅在调用start返回后调用pause为合理调用。await this.avTranscoder.pause();}}}// 恢复对应的转码流程。async resumeTranscoderingProcess() {if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {if (this.avTranscoder != undefined) { // 仅在调用pause返回后调用resume为合理调用。await this.avTranscoder.resume();}}}// 释放转码流程。async releaseTranscoderingProcess() {if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {if (this.avTranscoder != undefined) {// 1.释放转码实例。await this.avTranscoder.release();this.avTranscoder = undefined;// 2.关闭转码目标文件fd。}}}// 一个完整的【开始转码-暂停转码-恢复转码-转码完成】示例。async avTranscoderDemo() {await this.startTranscoderingProcess(); // 开始转码。await this.pauseTranscoderingProcess(); //暂停转码。await this.resumeTranscoderingProcess(); // 恢复转码。await this.releaseTranscoderingProcess(); // 释放转码。}
}