Object Storage Service:Generate a live transcoding playlist

How it works

With offline video transcoding, the entire video must finish transcoding before playback can start. Live transcoding works differently: playback begins immediately after the source video is uploaded. Only the segments being watched are transcoded in real time.

• Transcode during playback. No waiting. Playback starts as soon as the playlist is generated.

• Fast startup and seeking. Optimized transcoding delivers a playback experience similar to local playback.

• On-demand processing. Segments that are never played are never transcoded. Transcoded TS files can be deleted and regenerated on demand, which reduces storage costs.

• Broad format support. Over 300 audio and video input formats are supported.

• Customizable output. Transcoding parameters control video codec, resolution, bitrate, audio, and more.

Use cases

• Network drives: After a user uploads a video, the client selects the optimal resolution based on network conditions, ensuring real-time playback and device compatibility. Videos that are not frequently accessed are never transcoded, reducing storage costs.

• Video previews in chat applications: In messaging or social media apps, a video is playable immediately after it is sent. Videos in chat history can be periodically deleted and remain playable on demand.

• Online forums and blogs: Shared videos play without waiting for transcoding, delivering smooth playback at the selected resolution.

Supported formats

Live transcoding supports over 300 audio and video formats. The following table lists common supported formats.

Prerequisites

Before you begin, make sure that you have:

• Activated the Intelligent Media Management (IMM) service. For details, see Activate products

• Attached an IMM project to your OSS bucket. For console instructions, see Quick Start. For the API approach, see AttachOSSBucket

• The required permissions for IMM processing. For details, see Permissions

Usage notes

• Anonymous access will be denied.

• For additional details, see Live transcoding and GenerateVideoPlaylist API.

Parameters

Operation: hls/m3u8

Generate a playlist and sign the stream

Live transcoding involves two steps: generating the m3u8 playlist, then signing the stream URL for playback.

POST /example.avi?x-oss-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-process=hls/m3u8,ss_15000,t_1800000,vcodec_h264,fps_25,fpsopt_1,s_1280x720,sopt_1,scaletype_fit,arotate_1,vb_2000000,vbopt_1,acodec_aac,ar_44100,ac_2,ab_128000,abopt_1,st_10000,initd_30000|sys/saveas,o_b3V0b2JqcHJlZml4L21lZGlh,b_b3V0YnVja2V0

HTTP/1.1 200 OK
Server: AliyunOSS
Date: Wed, 25 May 2022 12:43:57 GMT
Content-Type: application/json;charset=utf-8
Content-Length: 161
Connection: keep-alive
x-oss-request-id: 628E2481184E20F26C000009
x-oss-server-time: 12437

{"Duration":1800,"RequestId":"********-37E6-5996-8425-********","VideoPlaylist":[{"FrameRate":"25","Resolution":"1280x720","Token":"f93c43079**********1269608ebc86e","URI":"oss://outbucket/outobjprefix/media.m3u8"}]}

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

# Specify the endpoint of the region where the bucket is located.
endpoint = 'yourEndpoint'

# Obtain access credentials from environment variables.
# Make sure OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET are set.
auth = oss2.ProviderAuth(EnvironmentVariableCredentialsProvider())

# The name of the destination bucket.
bucket_name = 'your-oss-bucket-name'

# Set key to the name of the generated playlist, for example, output/media.m3u8.
key = 'output/media.m3u8'

# Specify the bucket instance.
# Use the oss2.AuthV2 signing method.
bucket = oss2.Bucket(auth, 'https://oss-cn-hangzhou.aliyuncs.com', bucket_name)

# Set x-oss-process to hls/sign,live_1.
params = {}
params.update({oss2.Bucket.PROCESS: 'hls/sign,live_1'})

# Generate the signed URL.
# Set slash_safe to True so that OSS does not escape forward slashes (/)
# in the object path. Without this, the signed URL is unusable.
url = bucket.sign_url('GET', key, 7200, params=params, slash_safe=True)

# The generated URL can be played directly in any HLS player.
print(url)

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:10
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-PLAYLIST-TYPE:VOD
#EXTINF:10.0,
media-c14709808479b31566b50f2f8b93fe1a-0.ts
#EXTINF:10.0,
media-c14709808479b31566b50f2f8b93fe1a-1.ts
#EXTINF:10.0,
media-c14709808479b31566b50f2f8b93fe1a-2.ts
#EXTINF:10.0,
media-c14709808479b31566b50f2f8b93fe1a-3.ts
#EXT-X-ENDLIST

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:10
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-PLAYLIST-TYPE:VOD
#EXTINF:10.000,
media-c14709808479b31566b50f2f8b93fe1a-0.ts?x-oss-process=if_status_eq_404{hls/ts,from_b3V0cHV0L21lZGlhLm0zdTg}&x-oss-expires=1710457284&x-oss-signature-version=OSS2&x-oss-access-key-id=****fEAub****&x-oss-signature=****VR3gy****
#EXTINF:10.000,
media-c14709808479b31566b50f2f8b93fe1a-1.ts?x-oss-process=if_status_eq_404{hls/ts,from_b3V0cHV0L21lZGlhLm0zdTg}&x-oss-expires=1710457284&x-oss-signature-version=OSS2&x-oss-access-key-id=****fEAub****&x-oss-signature=****VR3gy****
#EXTINF:10.000,
media-c14709808479b31566b50f2f8b93fe1a-2.ts?x-oss-process=if_status_eq_404{hls/ts,from_b3V0cHV0L21lZGlhLm0zdTg}&x-oss-expires=1710457284&x-oss-signature-version=OSS2&x-oss-access-key-id=****fEAub****&x-oss-signature=****VR3gy****
#EXTINF:10.000,
media-c14709808479b31566b50f2f8b93fe1a-3.ts?x-oss-process=if_status_eq_404{hls/ts,from_b3V0cHV0L21lZGlhLm0zdTg}&x-oss-expires=1710457284&x-oss-signature-version=OSS2&x-oss-access-key-id=****fEAub****&x-oss-signature=****VR3gy****
#EXT-X-ENDLIST

Use an SDK

Generating a live transcoding playlist is a synchronous process. For SDK usage details, see Use an SDK.

Output files

When a playlist is generated, the system creates an m3u8 file and TS files at the specified output path prefix. The m3u8 file is created immediately. If a pre-transcoding duration is specified, TS files for that duration are generated asynchronously.

For example, with a 30-second pre-transcoding duration and 10-second segment duration, three TS files are created:

.
├── outobjprefix.m3u8
├── outobjprefix-92376fbb-171f-4259-913f-705f7ee02f2s-0.ts
├── outobjprefix-92376fbb-171f-4259-913f-705f7ee02f2s-1.ts
├── outobjprefix-92376fbb-171f-4259-913f-705f7ee02f2s-2.ts
├── outobjprefix-92376fbb-171f-4259-913f-705f7ee02f2s-3.ts

Segments that are not pre-transcoded are transcoded on demand during playback. If a video is never played, no additional TS files are generated. If playback starts at the 15-minute mark, transcoding begins from that point.

Feature details

FAQ