RMS offers two live event types: passthrough and ABR (Adaptive Bitrate). This guide explains how each type processes streams, the output ladders ABR produces, and which features each input protocol supports.
For step-by-step implementation, see Live streaming quickstart. For encoder configuration, see Live streaming: encoder configuration.
In this article:
What is passthrough
Passthrough is a live event type where RMS delivers the contribution stream as-is, without re-encoding. Your encoder sends a single bitrate stream over RTMP(S), SRT, or RTSP, and RMS forwards it to the packager.
When to use passthrough:
Long-running or 24/7 channels, since RMS doesn't re-encode the stream.
Your encoder produces the final quality and bitrate you want to deliver.
You want to minimize costs (no server-side transcoding).
What is Adaptive Bitrate
ABR is a live event type where RMS transcodes the contribution stream into multiple bitrate renditions, so players can switch quality based on the viewer's network conditions. Your encoder sends a single bitrate stream to RMS, and when you create the live event, you select either Standard 720p or Premium 1080p preset, which determines the output ladder.
When to use ABR:
You need multi-bitrate delivery for varying network conditions.
You want automatic quality adaptation for viewers.
ABR output ladders
These tables detail the optimal parameters for each resolution.
Output video streams for Standard 720p
Produces 4 renditions when the contribution feed is 720p or higher:
| Bitrate | Width | Height | MaxFPS | Profile |
|---|---|---|---|---|
| 3500 | 1280 | 720 | 30 | High |
| 2200 | 960 | 540 | 30 | High |
| 1350 | 704 | 396 | 30 | High |
| 850 | 512 | 288 | 30 | High |
Output video streams for Premium 1080p
Produces 5 renditions:
| Bitrate | Width | Height | MaxFPS | Profile |
|---|---|---|---|---|
| 5500 | 1920 | 1080 | 30 | High |
| 3500 | 1280 | 720 | 30 | High |
| 1600 | 960 | 540 | 30 | High |
| 800 | 640 | 360 | 30 | High |
| 400 | 480 | 270 | 30 | High |
Note: All renditions become available within 1-2 minutes after the live starts. A quick page reload will help see the full ABR ladder.
Your live stream will be encoded according to the input bitrate, width, and height. RMS does not upscale beyond the contribution feed's specifications.
If any parameter (bitrate, width, or height) falls below the minimum for a target resolution, that resolution will not be produced. Instead, renditions that exceed the input limit are dropped from the ladder. The ladder continues with the highest resolution all three parameters can support, with all the lower renditions in place.
Live streaming compatibility matrix
Not all protocols support all features. Verify compatibility before setup:
| Input protocol | Passthrough | ABR encoding | DVR (rewind and recording) |
|---|---|---|---|
| RTMP |
✓ Standard latency ✓ Low latency* |
✓ Standard latency ✗Low latency not supported |
✓ DVR |
| SRT |
✓ Standard latency ✓ Low latency* |
✓ Standard latency ✗Low latency not supported |
✓ DVR Passthrough (both HLS and MPEG-DASH) ✓ DVR ABR HLS ✗ DVR ABR MPEG-DASH not supported |
| RTSP |
✓ Standard latency ✗ Low latency not supported |
✗ Not supported | ✓ DVR |
*- Low latency requires HLS delivery. MPEG-DASH does not support LL.
Standard-latency events deliver both HLS and MPEG-DASH. Low latency disables DVR by default.
Next steps
Live streaming quickstart - create your first live event from start to stop.
- Live streaming: encoder configuration - contribution encoder settings.
Live streaming low latency best practices - reduce stream latency for real-time interactions.
Getting started with RMS API development - set up authentication and explore working code examples.