# Outputs · NDI · SRT · RTMP · External: Frame timing & colour

> Frame-locked outputs, genlock, and what goes on the wire.

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

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)

Every output is frame-locked. Its clock runs at the page's rate exactly — 59.94 is 60000/1001, not 60 — and the renderer is steered onto that clock, so each output frame carries exactly one new picture: no frame repeated, none skipped. Without the lock, a renderer at 60 fps feeding a 59.94 output skips a frame every 16.7 seconds, and two clocks at the same rate repeat and skip whenever their phases cross.

With a DeckLink card in the output, the output's clock follows the card's: the depth of the card's playout buffer steers it, a few hundred parts per million at most. A card locked to a house reference (genlock) therefore genlocks the graphics too; the External row says whether the card is genlocked or free running.

Outputs render the page's own pixels at any screen scale: a 1920×1080 page is a 1920×1080 frame on a Retina or 150% display too, never painted larger and shrunk.

| Status says | Meaning |
| --- | --- |
| 50 fps, frame-locked | Every frame of the last second went out, on time. |
| Locking to 59.94 fps… | The renderer is being brought onto the output clock — the first second or so after an output starts. |
| N repeated, N skipped | Frames the renderer delivered late in the last second (the machine was too busy). |
| SRT · N frames dropped (the encoder cannot keep up) | ffmpeg could not encode in real time: lower the bitrate or the page size, or use a faster machine. 4K H.264 in software needs a strong CPU. |
| N underruns (the card repeated a frame) | A DeckLink card ran out of frames; it repeated the last one rather than show nothing. |

| Output | On the wire |
| --- | --- |
| NDI | 8-bit BGRA with straight alpha, at the page's size and rate. |
| SRT, RTMP | H.264, 4:2:0, BT.709 matrix, legal range — and tagged so, so every decoder shows the colours that were authored. |
| External, fill only | 10-bit 4:2:2 Y'CbCr, BT.709, legal range, converted by Glider: the levels do not depend on the card. Choose 8-bit RGB to let the card convert instead. |
| External, fill + key or internal keyer | 8-bit RGB with alpha: the card makes the key from it. |
| Fullscreen | The page's sRGB values, untouched by the display's colour profile. |

> **8-bit source:** The renderer draws 8 bits a channel. 10-bit SDI carries those values with no rounding of its own on the way; it does not add detail that was never drawn.