HarmonyOS鸿蒙Next中使用AVPlayer添加视频内封字幕怎么实现

截至目前，官方暂未提供 AVPlayer“直接读取并显示内封字幕”的现成方案，当前仅支持视频播放前设置外挂字幕。

如果你的片源是 mkv、mp4 这类带内封字幕的文件，通常要先把字幕轨抽出来，转成 srt 等外挂字幕文件，再通过 AVPlayer 挂载播放。

如果要做内封字幕，可以参考以下两条建议方案：

1. 服务端或预处理阶段把内封字幕抽成 srt，比如用 ffmpeg 之类工具，先把视频里的字幕轨导出来，再在 HarmonyOS 端按外挂字幕方式接入；

2. 自己接入第三方解封装能力，自己解析 mkv/mp4 容器，把字幕轨读出来，再按时间轴自己绘制字幕层，这条工作量会明显大很多，AVPlayer 本身不能替你把这件事做完。

【先转外挂字幕：注意需在资源目录src/main/resources/rawfile/自备test.mp4以及test.srt】示例代码：

import { media } from '@kit.MediaKit';
import { common } from '@kit.AbilityKit';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct Index {
  @State subtitleText: string = '';
  private avPlayer: media.AVPlayer | null = null;
  private surfaceId: string = '';
  private xComponentController: XComponentController = new XComponentController();

  aboutToAppear() {
    this.initPlayer();
  }

  aboutToDisappear() {
    this.releasePlayer();
  }

  async initPlayer() {
    let context = this.getUIContext().getHostContext() as common.UIAbilityContext;
    this.avPlayer = await media.createAVPlayer();

    this.avPlayer.on('stateChange', async (state: string) => {
      if (!this.avPlayer) {
        return;
      }
      switch (state) {
        case 'initialized':
          if (this.surfaceId) {
            this.avPlayer.surfaceId = this.surfaceId;
          }
          await this.avPlayer.prepare();
          break;
        case 'prepared':
          await this.avPlayer.play();
          break;
      }
    });

    this.avPlayer.on('subtitleUpdate', (info: media.SubtitleInfo) => {
      this.subtitleText = info?.text ? info.text : '';
    });

    this.avPlayer.on('error', (err: BusinessError) => {
      console.error('player error: ' + err.code + ', ' + err.message);
    });

    let videoFd = await context.resourceManager.getRawFd('test.mp4');
    this.avPlayer.fdSrc = {
      fd: videoFd.fd,
      offset: videoFd.offset,
      length: videoFd.length
    };

    let subtitleFd = await context.resourceManager.getRawFd('test.srt');
    await this.avPlayer.addSubtitleFromFd(subtitleFd.fd, subtitleFd.offset, subtitleFd.length);
  }

  onSurfaceReady() {
    this.surfaceId = this.xComponentController.getXComponentSurfaceId();
    if (this.avPlayer && this.surfaceId && this.avPlayer.state === 'initialized') {
      this.avPlayer.surfaceId = this.surfaceId;
    }
  }

  async releasePlayer() {
    if (this.avPlayer) {
      try {
        await this.avPlayer.release();
      } catch (e) {
      }
      this.avPlayer = null;
    }
  }

  build() {
    Stack({ alignContent: Alignment.Bottom }) {
      XComponent({
        id: 'video_surface',
        type: 'surface',
        controller: this.xComponentController
      })
        .width('100%')
        .height(260)
        .onLoad(() => {
          this.onSurfaceReady();
        })

      Text(this.subtitleText)
        .fontSize(18)
        .fontColor(Color.White)
        .backgroundColor('#66000000')
        .padding(8)
        .margin({ bottom: 20, left: 12, right: 12 })
    }
    .width('100%')
  }
}