Understanding Preview and Program

pMix uses a preview/program workflow, also known as an A/B bus — the same model used by professional broadcast switchers like Blackmagic ATEM and Ross Carbonite.

Program

The program output is what your audience sees. It’s the live feed being streamed and/or recorded. In the source grid, the program source has a green border.

Only one source (or scene) is on program at a time.

Preview

The preview is your staging area. It shows the source you’re preparing to take live next. In the source grid, the preview source has a yellow border.

Use preview to:

  • Verify a camera angle before cutting to it
  • Check that an NDI source is connected and looks correct
  • Frame a shot before going on-air

Transitioning

When you tap the transition button, the preview source transitions to program:

  1. The preview source becomes the new program (green border)
  2. The old program source is automatically deselected
  3. The preview selection is cleared — tap another source to stage the next switch

The transition type (cut, dissolve, wipe, etc.) is configured in the Transitions panel.

Direct cuts

You can bypass preview entirely:

  • Double-tap a source in the grid to cut it directly to program
  • This is useful for fast-paced switching where you don’t need to preview first

Why use preview?

In a live production, mistakes are visible to your audience. The preview/program workflow gives you a safety net:

  • Verify before switching — Make sure the camera angle and audio are correct
  • Avoid dead sources — Don’t accidentally cut to a disconnected or black source
  • Smooth transitions — The transition always goes from the current program to the previewed source, giving you predictable results

Program output

Everything on program is sent to all active outputs simultaneously:

  • RTMP stream (YouTube, Twitch, etc.)
  • NDI output
  • SRT output
  • HLS output
  • Local recording

The program output includes any active overlays (text, images, countdowns) composited on top.