# Enable adaptive bitrate (/en/realtime-media/rtmp-gateway/build/optimize-quality-and-monitor-events/enable-adaptive-bitrate) > For AI agents: see the complete documentation index at [llms.txt](/llms.txt). 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 [#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 layers are independent. Enabling ABR does not automatically create a low stream. ## ABR configuration [#abr-configuration] Configure ABR encoding in stream configuration templates using the `settings.transcoding.video.simulcastStreamLayers` parameter. ### API endpoint [#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: | Parameter | Required | Description | | ------------ | -------- | ----------------------------------------------------------------------------------------------------------------------------------- | | `region` | Yes | Region for the streaming template. Supported values are `na`, `eu`, `ap`, and `cn`. Use the same region as the input source stream. | | `appId` | Yes | The App ID of your Agora project. | | `templateId` | Yes | The flow configuration template ID. The value can contain only letters and numbers and cannot exceed 12 bytes. | Relevant request fields: | Field | Required | Description | | ------------------------------------------------------------ | -------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `settings.transcoding.video.enabled` | Yes | Enables video transcoding. Set this field to `true` when you configure ABR layers. | | `settings.transcoding.video.width` | Yes | Encoding width of the main stream in pixels. Required when adaptive bitrate is enabled. | | `settings.transcoding.video.height` | Yes | Encoding height of the main stream in pixels. Required when adaptive bitrate is enabled. | | `settings.transcoding.video.fps` | No | Video encoding frame rate in fps. If omitted or set to `0`, the source stream frame rate is used. | | `settings.transcoding.video.bitrate` | No | Encoding bitrate of the main stream in Kbps. If omitted, the source stream bitrate is used. If set to `0`, Agora automatically chooses a bitrate based on width and height. | | `settings.transcoding.video.simulcastStreamLayers` | Yes | Array of layer transcoding parameters. If specified, ABR is enabled. | | `settings.transcoding.video.simulcastStreamLayers[].id` | Yes | Layer ID. Supported values range from `1` to `7`. | | `settings.transcoding.video.simulcastStreamLayers[].width` | No | Encoding width of the layer in pixels. If specified, it must be smaller than `video.width` and decrease monotonically as the layer ID increases. | | `settings.transcoding.video.simulcastStreamLayers[].height` | No | Encoding height of the layer in pixels. If specified, it must be smaller than `video.height` and decrease monotonically as the layer ID increases. | | `settings.transcoding.video.simulcastStreamLayers[].fps` | No | Encoding frame rate of the layer in fps. If specified, it must be smaller than `video.fps`. If omitted or set to `0`, the main stream frame rate is used. | | `settings.transcoding.video.simulcastStreamLayers[].bitrate` | Yes | Encoding bitrate of the layer in Kbps. It must be smaller than `video.bitrate` and decrease monotonically by layer ID. | ### Request example [#request-example] ```bash 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 [#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 [#layer-id-selection] Recommended mapping: | Layer ID | Resolution | | -------- | ----------------- | | 1 | 3840x2160 (4K) | | 2 | 2560x1440 (2K) | | 3 | 1920x1080 (1080p) | | 4 | 1280x720 (720p) | | 5 | 960x540 (540p) | | 6 | 854x480 (480p) | | 7 | 640x360 (360p) | ## Webhook notifications [#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](./receive-notifications.md).