# Outputs · NDI · SRT · RTMP · External: Sources, channels & signals

> What an output shows.

Glider documentation · Playout & On Air · Web page: https://cgglider.com/docs/outputs/sources/

Sections of this page: [How outputs work](https://cgglider.com/docs/outputs.md) · [Frame timing & colour](https://cgglider.com/docs/outputs/timing.md) · [Sources, channels & signals](https://cgglider.com/docs/outputs/sources.md) · [NDI](https://cgglider.com/docs/outputs/ndi.md) · [External (SDI) & fullscreen](https://cgglider.com/docs/outputs/external.md) · [SRT](https://cgglider.com/docs/outputs/srt.md) · [RTMP streaming](https://cgglider.com/docs/outputs/rtmp.md) · [API](https://cgglider.com/docs/outputs/api.md)

| Setting | Choices |
| --- | --- |
| Page | A page, or Default page (the machine's default, set at the top). |
| Bus | Program (what is on air) or Preview (the PVW row — what the next take puts on air). |
| Channel | All channels, or one: Program (graphics no rundown item drives, e.g. a bug), or Overlay 1–8 (only what that channel's items drive). A channel alone is how each overlay gets its own keyer. |

The same choices are available to any browser source as /view query parameters:

```text
/view/<id>?bus=preview          the preview bus
/view/<id>?channel=overlay2     one channel alone
/view/<id>?signal=fill          the graphic over black (a keyer's fill)
/view/<id>?signal=key           its alpha as white on black (a keyer's key)
```

A fill and key pair is two sources with the same bus and channel: signal=fill and signal=key. Semi-transparent graphics key correctly: 50% opacity is mid-grey in the key and half-bright in the fill.