Object Storage Service:Audio transcoding

Prerequisites

Before you begin, make sure that you have:

• An OSS bucket bound to an Intelligent Media Management (IMM) project. For setup instructions, see Quick start and AttachOSSBucket.

• The required permissions for audio transcoding.

• Access credentials configured as environment variables. Java and Python use OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET. Go additionally requires OSS_SESSION_TOKEN.

Use cases

• Format compatibility: Convert audio files to formats supported by a target device or player.

• Storage optimization: Transcode lossless audio (such as FLAC or WAV) to compressed lossy formats like MP3 to reduce storage footprint on mobile devices.

• Media streaming: Produce multiple bitrate versions of a source file to support adaptive streaming across different network conditions.

• Video post-processing: Convert audio tracks to compressed formats during video editing workflows to improve transfer efficiency.

How it works

Submit an asynchronous transcoding request using the x-oss-async-process header. The action is audio/convert. After the task completes, OSS saves the output audio to the path you specify with sys/saveas.

Audio transcoding is asynchronous only — the x-oss-process header used for synchronous image processing is not supported.

Parameters

Action: audio/convert

Use sys/saveas to specify the output path and notify to receive a completion notification. See sys/saveas and Use the notification feature.

Limitations

• Audio transcoding does not support adjusting bit depth, except for FLAC output (use adepth). For bit depth control on video tracks, see Video transcoding.

• Anonymous requests are denied. Authentication is required.

• Only the Java, Python, and Go SDKs support asynchronous audio transcoding.

Use the RESTful API

All examples use the x-oss-async-process header to submit asynchronous transcoding tasks.

POST /example.mp3?x-oss-async-process HTTP/1.1
Host: video-demo.oss-cn-hangzhou.aliyuncs.com
Date: Fri, 28 Oct 2022 06:40:10 GMT
Authorization: OSS4-HMAC-SHA256 Credential=LTAI********************/20250417/cn-hangzhou/oss/aliyun_v4_request,Signature=a7c3554c729d71929e0b84489addee6b2e8d5cb48595adfc51868c299c0c218e

x-oss-async-process=audio/convert,ss_10000,t_60000,f_aac,ab_96000|sys/saveas,b_b3V0YnVja2V0,o_b3V0b2JqcHJlZml4LnthdXRvZXh0fQo/notify,topic_QXVkaW9Db252ZXJ0

POST /example.wav?x-oss-async-process HTTP/1.1
Host: video-demo.oss-cn-hangzhou.aliyuncs.com
Date: Fri, 28 Oct 2022 06:40:10 GMT
Authorization: OSS4-HMAC-SHA256 Credential=LTAI********************/20250417/cn-hangzhou/oss/aliyun_v4_request,Signature=a7c3554c729d71929e0b84489addee6b2e8d5cb48595adfc51868c299c0c218e

x-oss-async-process=audio/convert,f_opus,ab_96000,ar_48000,ac_2|sys/saveas,b_b3V0YnVja2V0,o_b3V0b2JqLnthdXRvZXh0fQo/notify,topic_QXVkaW9Db252ZXJ0

Use OSS SDKs

import com.aliyun.oss.ClientBuilderConfiguration;
import com.aliyun.oss.OSS;
import com.aliyun.oss.OSSClientBuilder;
import com.aliyun.oss.common.auth.CredentialsProviderFactory;
import com.aliyun.oss.common.auth.EnvironmentVariableCredentialsProvider;
import com.aliyun.oss.common.comm.SignVersion;
import com.aliyun.oss.model.AsyncProcessObjectRequest;
import com.aliyun.oss.model.AsyncProcessObjectResult;
import com.aliyuncs.exceptions.ClientException;

import java.util.Base64;

public class Demo {
    public static void main(String[] args) throws ClientException {
        // Endpoint of the region where the bucket is located
        String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        // Region ID of the bucket
        String region = "cn-hangzhou";
        // Load credentials from environment variables OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET
        EnvironmentVariableCredentialsProvider credentialsProvider = CredentialsProviderFactory.newEnvironmentVariableCredentialsProvider();
        String bucketName = "examplebucket";
        String targetKey = "dest.aac";
        String sourceKey = "src.mp3";

        ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
        clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);
        OSS ossClient = OSSClientBuilder.create()
                .endpoint(endpoint)
                .credentialsProvider(credentialsProvider)
                .clientConfiguration(clientBuilderConfiguration)
                .region(region)
                .build();

        try {
            // Transcoding parameters: start at 10 s, duration 60 s, output AAC at 96 kbit/s
            String style = String.format("audio/convert,ss_10000,t_60000,f_aac,ab_96000");
            // Base64-encode the bucket name and output object key for sys/saveas
            String bucketEncoded = Base64.getUrlEncoder().withoutPadding().encodeToString(bucketName.getBytes());
            String targetEncoded = Base64.getUrlEncoder().withoutPadding().encodeToString(targetKey.getBytes());
            String process = String.format("%s|sys/saveas,b_%s,o_%s/notify,topic_QXVkaW9Db252ZXJ0", style, bucketEncoded, targetEncoded);

            AsyncProcessObjectRequest request = new AsyncProcessObjectRequest(bucketName, sourceKey, process);
            AsyncProcessObjectResult response = ossClient.asyncProcessObject(request);
            System.out.println("EventId: " + response.getEventId());
            System.out.println("RequestId: " + response.getRequestId());
            System.out.println("TaskId: " + response.getTaskId());
        } finally {
            ossClient.shutdown();
        }
    }
}

# -*- coding: utf-8 -*-
import base64
import oss2
from oss2.credentials import EnvironmentVariableCredentialsProvider

def main():
    # Load credentials from environment variables
    auth = oss2.Auth(EnvironmentVariableCredentialsProvider())
    endpoint = 'https://oss-cn-hangzhou.aliyuncs.com'
    bucket = oss2.Bucket(auth, endpoint, 'examplebucket')

    source_key = 'src.mp3'
    target_key = 'dest.aac'

    # Transcoding parameters: start at 10 s, duration 60 s, output AAC at 96 kbit/s
    style = 'audio/convert,ss_10000,t_60000,f_aac,ab_96000'

    # Base64-encode the bucket name and output object key for sys/saveas
    bucket_name_encoded = base64.urlsafe_b64encode('examplebucket'.encode()).decode().rstrip('=')
    target_key_encoded = base64.urlsafe_b64encode(target_key.encode()).decode().rstrip('=')
    process = f"{style}|sys/saveas,b_{bucket_name_encoded},o_{target_key_encoded}/notify,topic_QXVkaW9Db252ZXJ0"

    try:
        result = bucket.async_process_object(source_key, process)
        print(f"EventId: {result.event_id}")
        print(f"RequestId: {result.request_id}")
        print(f"TaskId: {result.task_id}")
    except Exception as e:
        print(f"Error: {e}")


if __name__ == "__main__":
    main()

package main

import (
	"encoding/base64"
	"fmt"
	"log"
	"os"

	"github.com/aliyun/aliyun-oss-go-sdk/oss"
)

func main() {
	// Load credentials from environment variables OSS_ACCESS_KEY_ID, OSS_ACCESS_KEY_SECRET, and OSS_SESSION_TOKEN
	provider, err := oss.NewEnvironmentVariableCredentialsProvider()
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(-1)
	}

	// Create an OSS client for the bucket's region
	client, err := oss.New("https://oss-cn-hangzhou.aliyuncs.com", "", "", oss.SetCredentialsProvider(&provider), oss.AuthVersion(oss.AuthV4), oss.Region("cn-hangzhou"))
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(-1)
	}

	bucketName := "examplebucket"
	bucket, err := client.Bucket(bucketName)
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(-1)
	}

	sourceKey := "src.mp3"
	targetKey := "dest.aac"

	// Transcoding parameters: start at 10 s, duration 60 s, output AAC at 96 kbit/s
	style := "audio/convert,ss_10000,t_60000,f_aac,ab_96000"

	// Base64-encode the bucket name and output object key for sys/saveas
	bucketNameEncoded := base64.URLEncoding.EncodeToString([]byte(bucketName))
	targetKeyEncoded := base64.URLEncoding.EncodeToString([]byte(targetKey))
	process := fmt.Sprintf("%s|sys/saveas,b_%v,o_%v/notify,topic_QXVkaW9Db252ZXJ0", style, bucketNameEncoded, targetKeyEncoded)

	result, err := bucket.AsyncProcessObject(sourceKey, process)
	if err != nil {
		log.Fatalf("Failed to async process object: %s", err)
	}

	fmt.Printf("EventId: %s\n", result.EventId)
	fmt.Printf("RequestId: %s\n", result.RequestId)
	fmt.Printf("TaskId: %s\n", result.TaskId)
}

What's next

• sys/saveas — save transcoded output to a specified OSS path

• Use the notification feature — receive a callback when transcoding completes

• Video transcoding — transcode video files and adjust parameters including bit depth