Overview of Alibaba Cloud CDN Live Streaming Architecture and Key Technologies

Video is a sequence of images displayed at more than 24 frames per second, creating a smooth visual effect based on the persistence of vision principle.

Media transcoding converts audio, video, or other multimedia from one encoding format to another, while a Content Delivery Network (CDN) provides services such as streaming servers, load balancing, routing, video transcoding, recording, anti‑hotlinking, and performance optimization.

The article introduces Alibaba Cloud CDN live streaming system from the perspectives of overview, architecture, business functions, and scenarios.

1. Video‑related terminology

Bitrate: The amount of data transmitted per unit time, usually expressed in kbps. Higher bitrate generally yields higher quality but larger file size.

Frame: The smallest unit of video data, equivalent to a single still image; a series of frames creates motion.

Frame rate (fps): Number of frames displayed per second; higher fps provides smoother animation, though gains diminish beyond the display's refresh rate.

2. Live streaming overview

Live streaming and video‑on‑demand (VOD) both deliver video data from servers to clients, but VOD allows random access (fast‑forward, rewind) while live streaming does not. Live streaming tags each frame with a timestamp and streams it continuously, forming a publish‑subscribe model.

The live streaming workflow includes video capture, preprocessing, encoding, push‑stream, transcoding, distribution, and client playback.

3. Live streaming architecture

Capture: Video is captured from iOS, Android, or PC devices (e.g., OBS on PC).

Pre‑processing: Includes beauty filters, watermarks, blur effects, etc.

Encoding: Balances bitrate and quality; iOS often uses hardware encoding, Android mainly software encoding.

Push‑stream & transcoding: Streams are sent to servers and transcoded to various protocols such as RTMP, HLS, and FLV.

Distribution: CDN accelerates delivery to support massive concurrent viewers.

Client playback: Decoding and rendering on iOS, Android, Flash, VLC, HTML5, etc., with focus on low latency and fast start.

4. Detailed CDN architecture

Push streams typically use RTMP; playback can use RTMP, HTTP‑FLV, or HLS. Popular push‑stream tools include OBS, mobile apps, and FFmpeg. The CDN network consists of over 700 domestic nodes and 300 overseas nodes, providing intelligent scheduling and edge delivery.

The publishing side sends streams to the server, which then distributes them to multiple subscribers through a cascade of publish‑subscribe relationships.

5. Business functions and scenarios

Key functions include transcoding (with quality and bitrate adjustments), watermarking, dynamic templates, delayed transcoding, periodic screenshots, dynamic configuration, recording, authentication, anti‑hotlinking, blacklisting, and various APIs for stream management.

Monitoring captures metrics such as bitrate, traffic, online viewers, and frame rate; sudden frame‑rate drops indicate network jitter, prompting frame loss handling.

Typical application scenarios:

UGC interactive live: Platforms like Yizhibo, Inke offering chat, co‑broadcast, etc.

E‑commerce live: Platforms such as Taobao Live handling promotional spikes.

Sports events / large‑scale variety shows: Services for CCTV5 and similar broadcasters.

Game live: Supports capture devices, recording for later VOD (e.g., Quanmin, Panda).

Online education / finance live: Provides authentication, anti‑hotlinking, and URL encryption for education and financial platforms.

More than half of video live‑streaming and VOD platforms currently use Alibaba Cloud's live streaming services, which continue to evolve to build a comprehensive video technology ecosystem.