Dual Stream Mode

Dual stream mode refers to publishing both a high-quality (large) and a low-quality (small) video stream when sharing video resources.

The SDK enables dual stream publishing by default, automatically generating both streams for each video publisher. The small stream's resolution automatically follows the large stream's settings.

tip

In multi-party RTC calls, dual stream mode effectively reduces downstream bandwidth consumption. Subscribers can optionally request the small stream as needed.

The resolution mapping between small and large streams is as follows:

Large Stream Resolution	Small Stream Resolution	Aspect Ratio
176X144	176X144	11:9
180X180	180X180	1:1
256X144	256X144	16:9
240X180	240X180	4:3
320X180	256X144	16:9
240X240	180X180	1:1
320X240	240X180	4:3
360X360	180X180	1:1
480X360	240X180	4:3
640X360	256X144	16:9
480X480	180X180	1:1
640X480	240X180	4:3
720X480	240X180	3:2
848X480	256X144	9:5
960X720	240X180	4:3
1280X720	256X144	16:9
1920X1080	256X144	16:9

Enabling/Disabling Dual Stream

Configure dual stream mode during engine initialization by specifying the video setup parameters. When enabled, publishers will automatically generate both streams.

/// Enable dual stream during engine creation
RCRTCVideoSetup videoSetup = RCRTCVideoSetup.create(enableTinyStream: true);
RCRTCEngineSetup engineSetup = RCRTCEngineSetup.create(videoSetup: videoSetup);
engine = RCRTCEngine.create(engineSetup);

/// Disable dual stream during engine creation
RCRTCVideoSetup videoSetup = RCRTCVideoSetup.create(enableTinyStream: false);
RCRTCEngineSetup engineSetup = RCRTCEngineSetup.create(videoSetup: videoSetup);
engine = RCRTCEngine.create(engineSetup);

Configuring Small Stream Properties

When dual stream is enabled, set small stream parameters by passing true to the tiny parameter in setVideoConfig:

RCRTCVideoConfig config = RCRTCVideoConfig.create(
    minBitrate: 200,
    maxBitrate: 900,
    fps: RCRTCVideoFps.fps_15,
    resolution: RCRTCVideoResolution.resolution_480_640,
);
engine.setVideoConfig(config, true);

Switching Streams as Subscriber

If remote users enabled dual stream before joining, local subscribers can request either stream via the tiny parameter in subscribe:

/// Subscribe to large stream
engine.subscribe(userId, RCRTCMediaType.audio_video, false);

/// Subscribe to small stream
engine.subscribe(userId, RCRTCMediaType.audio_video, true);