Using AVTranscoder to Transcode Videos (ArkTS)

You can use the AVTranscoder to implement video transcoding. You can check whether the current device supports the AVTranscoder by calling canIUse. If the return value of canIUse("SystemCapability.Multimedia.Media.AVTranscoder") is true, the transcoding capability can be used.

This topic describes how to use the AVTranscoder to implement video transcoding, covering the process of starting, pausing, resuming, and exiting transcoding.

How to Develop

Read AVTranscoder for the API reference.

Create an avTranscoder instance.

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

let avTranscoder: media.AVTranscoder;
media.createAVTranscoder().then((transcoder: media.AVTranscoder) => {
  avTranscoder = transcoder;
  // Perform other operations after avTranscoder is assigned a value.
}, (error: BusinessError) => {
  console.error(`createAVTranscoder failed`);
});

Set the events to listen for.

Event Type	Description
complete	Mandatory; used to listen for the completion of transcoding.
error	Mandatory; used to listen for AVTranscoder errors.

import { BusinessError } from '@kit.BasicServicesKit';

// Callback function for the completion of transcoding.
avTranscoder.on('complete', () => {
  console.log(`transcoder is completed`);
  // Listen for the transcoding completion event and call release.
});

// Callback function for errors.
avTranscoder.on('error', (err: BusinessError) => {
  console.error(`avTranscoder failed, code is ${err.code}, message is ${err.message}`);
});

Set the FD of the source video file.
NOTE

The fdSrc value in the code snippet below is for reference only. You need to check the media asset validity and set fdSrc based on service requirements.
- If local files are used for transcoding, ensure that the files are available and the application sandbox path is used for access. For details about how to obtain the application sandbox path, see Obtaining Application File Paths. For details about the application sandbox and how to push files to the application sandbox directory, see File Management.
- You can also use ResourceManager.getRawFd() to obtain the FD of a file packed in the HAP file. For details, see ResourceManager API Reference.
```
import resourceManager from '@ohos.resourceManager';
import { common } from '@kit.AbilityKit';

let context = getContext(this) as common.UIAbilityContext;
let fileDescriptor = await context.resourceManager.getRawFd('H264_AAC.mp4');
// Set fdSrc used for transcoding.
this.avTranscoder.fdSrc = fileDescriptor;
```
Set the FD of the target video file.

NOTE

fdDst specifies the FD of the output file after transcoding. The value is a number. You must call ohos.file.fs of Core File Kit to implement access to the application file. For details, see Application File Access and Management.
```
// Set fdDst of the output file.
this.avTranscoder.fdDst = 55; // Obtain the file descriptor of the created video file by referring to the sample code in Application File Access and Management.
```

Set video transcoding parameters and call prepare().

NOTE

Only transcoding-related parameters are set in the input parameter avConfig of the prepare() API.

Only the supported transcoding formats can be used due to the limited demultiplexing, multiplexing, encoding, and decoding capabilities.

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

let avConfig: media.AVTranscoderConfig = {
  audioBitrate: 100000, // Audio bit rate.
  audioCodec: media.CodecMimeType.AUDIO_AAC, // Audio encoding format.
  fileFormat: media.ContainerFormatType.CFT_MPEG_4, // Container format.
  videoBitrate: 2000000, // Video bit rate.
  videoCodec: media.CodecMimeType.VIDEO_AVC, // Video encoding format.
  videoFrameWidth: 640, // Video frame width: 640.
  videoFrameHeight: 480, // Video frame height: 480.
};
avTranscoder.prepare(avConfig).then(() => {
  console.log('Invoke prepare succeeded.');
}, (err: BusinessError) => {
  console.error(`Invoke prepare failed, code is ${err.code}, message is ${err.message}`);
});

Call start() to start transcoding.

// Start transcoding.
avTranscoder.start();

Call pause() to pause transcoding.

// Pause transcoding.
avTranscoder.pause();

Call resume() to resume transcoding.

// Resume transcoding.
avTranscoder.resume();

Call cancel() to cancel transcoding.

// Cancel transcoding.
avTranscoder.cancel();

Call release() to destroy the instance and exit transcoding.
```
// Destroy the instance.
avTranscoder.release();
```

Sample Code

Refer to the sample code below to implement transcoding, covering the process of starting, pausing, resuming, and exiting transcoding.

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

export class AVTranscoderDemo {
  private avTranscoder: media.AVTranscoder | undefined = undefined;
  private avConfig: media.AVTranscoderConfig = {
    audioBitrate: 100000, // Audio bit rate.
    audioCodec: media.CodecMimeType.AUDIO_AAC, // Audio encoding format.
    fileFormat: media.ContainerFormatType.CFT_MPEG_4, // Container format.
    videoBitrate: 200000, // Video bit rate.
    videoCodec: media.CodecMimeType.VIDEO_AVC, // Video encoding format.
    videoFrameWidth: 640, // Video frame width.
    videoFrameHeight: 480, // Video frame height.
  };

  // Set AVTranscoder callback functions.
  setAVTranscoderCallback() {
    if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {
      if (this.avTranscoder != undefined) {
        // Callback function for the completion of transcoding.
        this.avTranscoder.on('complete', async () => {
          console.log(`AVTranscoder is completed`);
          await this.releaseTranscoderingProcess();
        });
        // Callback function for errors.
        this.avTranscoder.on('error', (err: BusinessError) => {
          console.error(`AVTranscoder failed, code is ${err.code}, message is ${err.message}`);
        });
      }
    }
  }

  // Process of starting transcoding.
  async startTranscoderingProcess() {
    if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {
      if (this.avTranscoder != undefined) {
        await this.avTranscoder.release();
        this.avTranscoder = undefined;
      }
      // 1. Create an avTranscoder instance.
      this.avTranscoder = await media.createAVTranscoder();
      this.setAVTranscoderCallback();
      // 2. Obtain the source file FD and output file FD and assign them to avTranscoder. For details, see the FilePicker document.
      let context = getContext(this) as common.UIAbilityContext;
      let fileDescriptor = await context.resourceManager.getRawFd('H264_AAC.mp4');
      this.avTranscoder.fdSrc = fileDescriptor;
      this.avTranscoder.fdDst = 55;
      // 3. Set transcoding parameters to complete the preparations.
      await this.avTranscoder.prepare(this.avConfig);
      // 4. Start transcoding.
      await this.avTranscoder.start();
    }
  }

  // Process of pausing transcoding.
  async pauseTranscoderingProcess() {
    if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {
      if (this.avTranscoder != undefined) { // It is reasonable to call pause only after start is called and returns a value.
        await this.avTranscoder.pause();
      }
    }
  }

  // Resume the transcoding process.
  async resumeTranscoderingProcess() {
    if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {
      if (this.avTranscoder != undefined) { // It is reasonable to call resume only after pause is called and returns a value.
        await this.avTranscoder.resume();
      }
    }
  }

  // Release the transcoding process.
  async releaseTranscoderingProcess() {
    if (canIUse("SystemCapability.Multimedia.Media.AVTranscoder")) {
      if (this.avTranscoder != undefined) {
        // 1. Release the avTranscoder instance.
        await this.avTranscoder.release();
        this.avTranscoder = undefined;
        // 2. Close the FD of the output file.
      }
    }
  }

  // A complete example of starting, pausing, resuming, and exiting transcoding.
  async avTranscoderDemo() {
    await this.startTranscoderingProcess(); // Start transcoding.
    await this.pauseTranscoderingProcess(); // Pause transcoding.
    await this.resumeTranscoderingProcess(); // Resume transcoding.
    await this.releaseTranscoderingProcess(); // Exit transcoding.
  }
}