# Outputs · NDI · SRT · RTMP · External: Who draws what

> The output engine draws what the outputs send. Monitors and viewers draw the page themselves.

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

Sections of this page: [If something crashes](https://cgglider.com/docs/outputs.md) · [Who draws what](https://cgglider.com/docs/outputs/render-mode.md) · [How outputs work](https://cgglider.com/docs/outputs/model.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) · [Web](https://cgglider.com/docs/outputs/web.md) · [API](https://cgglider.com/docs/outputs/api.md)

One output engine draws each picture the outputs send. Outputs of the same page, bus and channel share one renderer and one frame clock, so NDI, SRT, RTMP, SDI and Web send the same frame at the same moment. One channel alone is a separate picture with its own renderer.

| Surface | Who draws it | Why |
| --- | --- | --- |
| NDI, SRT, RTMP, SDI and Web (/out) | The output engine, at the show's frame rate. | These need the pixels, and the engine makes them once. |
| Multiview Preview, Program and scene cards | The editor window, from the same program state, with the same scene renderer the engine runs. | A Cut changes Preview and Program in the same frame, and a scene card needs no renderer of its own. |
| Program deck › Return | The output engine: its own picture at half size, up to 30 times a second. | A confidence check of what the outputs actually send. If the renderer freezes, Return says so. |
| /view: a browser source, the Monitors link, Open live | The browser itself, at its display's rate, with alpha. | Smooth on any computer. Add ?renderer=shared to see the engine's picture instead, as Return shows it. |
| Fullscreen outputs | Their own window, on that display. | Full frame rate, without copying pictures from one process to another. |

> **Why monitors do not show the engine's pictures:** Every picture the engine hands to another window is copied off the graphics card, converted, compressed and decoded again. With a renderer for every scene, Preview and Program, that work outgrew the engine on a laptop: its watchdog then reloaded every renderer at once and the outputs stalled with them. The scene renderer in the editor is the same code the engine runs, and the render parity suite keeps their frames identical.

> **Go Live still decides what airs:** On a page that is not live, NDI, SRT, RTMP and SDI hold where they are while you rehearse takes on the monitors. Going live puts the page on the outputs.