Enable adaptive bitrate

Adaptive Bitrate (ABR) streaming delivers multiple video quality levels from a single source, allowing viewers to automatically switch between different bitrates based on their network conditions and device capabilities. This ensures optimal viewing experience by reducing buffering and maintaining the highest possible quality for each viewer's situation.

This guide explains how to configure Adaptive Bitrate (ABR) encoding for video transcoding in Media Gateway.

Understand the tech

ABR works by encoding the same video content at multiple resolutions and bitrates, called layers. Viewers can then select or automatically switch between different layers based on their available bandwidth and device performance. Media Gateway supports ABR through the simulcastStreamLayers configuration in stream templates. When enabled, the system creates multiple encoding layers from your source stream.

Following are the key ABR concepts:

• Source stream: The original stream pushed by the client without transcoding.
• Main stream: The primary transcoded stream output by Media Gateway when video transcoding is enabled. Resolution does not exceed the source stream resolution.
• Layer: Additional streams with lower bitrates that Media Gateway outputs based on your configuration.
• Layer ID: A unique identifier for each layer stream, ranging from 1 to 7.
• Low stream: A lower-quality stream option that was available before full ABR support. It is now implemented as Layer ID 7 to maintain compatibility with existing applications that expect this stream type.

ABR configuration

Configure ABR encoding in stream configuration templates using the settings.transcoding.video.simulcastStreamLayers parameter.

API endpoint

Use the Create or reset template API to configure ABR layers:

• Method: PUT
• Endpoint: https://api.agora.io/{region}/v1/projects/{appId}/rtls/ingress/stream-templates/{templateId}
• Authentication: HTTP Basic authentication or HMAC authentication

Path parameters:

Relevant request fields:

Request example

curl --request PUT \
  --url https://api.agora.io/${region}/v1/projects/${appId}/rtls/ingress/stream-templates/${templateId} \
  --header 'Content-Type: application/json' \
  --header 'Authorization: Basic XXXXXX' \
  --data '{
    "settings": {
      "transcoding": {
        "video": {
          "enabled": true,
          "width": 1920,
          "height": 1080,
          "fps": 30,
          "bitrate": 3800,
          "simulcastStreamLayers": [
            { "id": 1, "width": 1280, "height": 720, "fps": 30, "bitrate": 2400 },
            { "id": 2, "width": 960, "height": 540, "fps": 30, "bitrate": 1500 },
            { "id": 3, "width": 854, "height": 480, "fps": 30, "bitrate": 800 },
            { "id": 7, "width": 640, "height": 360, "fps": 30, "bitrate": 500 }
          ]
        },
        "audio": {
          "enabled": true,
          "profile": 3
        }
      }
    }
  }'

Configuration requirements

• Maximum 5 simultaneous layers per stream
• Specify at least one dimension for the main stream when ABR is enabled
• Specify at least one dimension for each ABR layer
• Specify bitrates in decreasing order by Layer ID
• If specified, layer width and height must decrease monotonically as the Layer ID increases
• If specified, each layer FPS must be lower than the main stream FPS
• Clients must specify the Layer ID when subscribing to receive the corresponding quality layer

Layer ID selection

When specifying layer IDs, best practice is to bind each ID to a specific resolution. This enables you to dynamically add or delete ABR layers without needing to modify the mapping between layer ID and resolution.

Recommended Layer ID mapping:

Example configuration:

If your source stream is 1080p and you want to output 1080p, 720p, 480p, and 360p video streams, configure the ABR layer IDs as follows:

Webhook notifications

To help you monitor the ABR configuration for each stream, Media Gateway provides this information through webhooks. When video transcoding is enabled, the live_stream_connected event includes the transcoding configuration details for your stream. See Receive notifications about channel events.

Example notification payload

The transcoding.video.simulcastStreamLayers array shows the active ABR layers for this stream, including their resolution, bitrate, and Layer ID configuration.

{
    "beginAt": "2025-03-11T17:56:23.60Z",
    "domain": "rtls-ingress-test-cn.agoramdn.com",
    "region": "dev-cn",
    "rtcInfo": {
        "channel": "abrtest0224",
        "uid": "1000"
    },
    "sid": "66ff5811-7baa-0298-8244-f2de5ae2a047",
    "streamKey": "123456rlg-RSQ_TqkhqgF373zAll4vz",
    "transcoding": {
        "audio": {
            "enabled": true,
            "profile": 3
        },
        "video": {
            "enabled": true,
            "bitrate": 3000,
            "fps": 30,
            "width": 1920,
            "height": 1080,
            "simulcastStreamLayers": [
                {
                    "id": 4,
                    "bitrate": 2000,
                    "fps": 30,
                    "height": 720,
                    "width": 1280
                },
                {
                    "id": 5,
                    "bitrate": 1200,
                    "fps": 30,
                    "height": 540,
                    "width": 960
                },
                {
                    "id": 7,
                    "bitrate": 700,
                    "fps": 30,
                    "height": 360,
                    "width": 640
                }
            ]
        }
    }
}

Subscriber-side ABR stream

Subscribers can choose ABR layers on the receiving side and let the SDK adapt to changing network conditions.

Integration guidelines

• Web SDK:

  • Minimum version: 4.22.1 or later
  • Recommended: Use the latest SDK from the official website
  • Note: To use the latest Agora Web FLS Player, contact technical support

• Native SDK:

  • Minimum version: 4.3.2 or later
  • Recommended: Use the latest SDK from the official website

Stream quality levels

Native SDK: Subscriber-side APIs

Configure remote subscriber fallback

• API: setRemoteSubscribeFallbackOption(StreamFallbackOptions option)

• Description: Sets the fallback option for subscribed audio and video streams under poor network conditions. In suboptimal network environments, real-time audio and video quality may degrade. Use this method to set a StreamFallbackOptions value. When the downlink network is weak and the quality is severely affected, the SDK automatically reduces the video stream to a lower layer to maintain smooth playback. The SDK continuously monitors the network and restores the higher layer when conditions improve.

  Specify the minimum acceptable fallback level:

  • To fall back to a lower video stream, use STREAM_FALLBACK_OPTION_VIDEO_STREAM_LOW.
  • To fall back to audio only, use STREAM_FALLBACK_OPTION_AUDIO_ONLY.

• Supported values:

  • STREAM_FALLBACK_OPTION_DISABLED
  • STREAM_FALLBACK_OPTION_VIDEO_STREAM_LOW
  • STREAM_FALLBACK_OPTION_AUDIO_ONLY
  • STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_1
  • STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_2
  • STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_3
  • STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_4
  • STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_5
  • STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_6

• Enum: StreamFallbackOptions

  enum StreamFallbackOptions {
      STREAM_FALLBACK_OPTION_DISABLED,
      STREAM_FALLBACK_OPTION_VIDEO_STREAM_LOW,
      STREAM_FALLBACK_OPTION_AUDIO_ONLY,
      STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_1,
      STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_2,
      STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_3,
      STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_4,
      STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_5,
      STREAM_FALLBACK_OPTION_VIDEO_STREAM_LAYER_6
  }

Manual stream selection

• API: setRemoteVideoStreamType(int uid, VideoStreamType streamType)
• Description: Sets the stream type to subscribe to for a specific remote user.

Set the default stream type

• API: setRemoteDefaultVideoStreamType(VideoStreamType streamType)

• Description: Sets the default stream type for new subscriptions.

• Enum: VideoStreamType

  enum VideoStreamType {
      VIDEO_STREAM_HIGH,
      VIDEO_STREAM_LOW,
      VIDEO_STREAM_LAYER_1,
      VIDEO_STREAM_LAYER_2,
      VIDEO_STREAM_LAYER_3,
      VIDEO_STREAM_LAYER_4,
      VIDEO_STREAM_LAYER_5,
      VIDEO_STREAM_LAYER_6;
  }

Web SDK: Subscriber-side APIs

Enable bandwidth estimation

• API: .setParameter("ENABLE_AUT_CC", true);
• Description: AUT-CC is a server-side Bandwidth Estimation (BWE) mechanism that relies on packet loss. Its main inputs include the number of packets, packet size, feedback on packet loss, and the timing of that feedback. The output is the currently available bandwidth.

Configure remote subscriber fallback

• API: setStreamFallbackOption(uid: UID, fallbackType: RemoteStreamFallbackType): Promise<void>

• Description: Enables automatic switching on the subscriber side under poor network conditions.

• Example:

  // the range supports up to LOW_STREAM
  client.setStreamFallbackOption(uid, 1);

Manual stream selection

• API: setRemoteVideoStreamType(uid: UID, streamType: RemoteStreamType): Promise<void>

• Description: Selects the high or low stream for a specific remote user.

• Example:

  client.setRemoteVideoStreamType(uid, 0); // HIGH_STREAM = 0

• Enum: VideoStreamType

  enum VideoStreamType {
      HIGH_STREAM,
      LOW_STREAM,
      HIGH_STREAM_LAYER1,
      HIGH_STREAM_LAYER2,
      HIGH_STREAM_LAYER3,
      HIGH_STREAM_LAYER4,
      HIGH_STREAM_LAYER5,
      HIGH_STREAM_LAYER6;
  }

For manual switching, consider the network conditions. The following example shows how to obtain the network status:

const NetworkQualityDesc = [
        "Unknown",
        "Excellent",
        "Good",
        "Poor",
        "Bad",
        "Very Bad",
        "Down",
];
client.on("network-quality", (quality) => {
        uplinkQuality = NetworkQualityDesc[quality.uplinkNetworkQuality];
        downlinkQuality = NetworkQualityDesc[quality.downlinkNetworkQuality];
        console.log(uplinkQuality, downlinkQuality);
});

Set the default stream type

• API: setRemoteDefaultVideoStreamType(streamType: RemoteStreamType): Promise<void>
• Description: Sets the default stream type for all remote users.