vision-mixers — Mix & Effects

This is where production happens live: cutting between sources, building layered looks, adding graphics and effects, and mixing audio — all in software, changed on the fly without dropping a frame.

Why it matters

A vision mixer is the heart of any live gallery. Phrame delivers it as composable software rather than a fixed console:

Build the mixer you need. Small, focused components — switch, scale, composite, overlay, 2D DVE, audio mix — combine into exactly the production chain a show requires.
Change it live. Runtime control is event-driven; operator actions become live mixer changes without interrupting the frames in flight.
Scriptable. Control logic is embedded Lua, so behaviours and automation are expressed as configuration, not custom builds.
Same bus, no cabling. Components pass frames over the shared-memory bus — no SDI routing, no physical patching.

In one line: a gallery’s worth of switching, graphics, and audio — as software you compose and re-compose at will.

How it works

Each component is its own executable; you wire them by connecting one component’s bus output to the next’s input.

Component	Purpose
`phrame_switch`	Route / switch between input sources
`phrame_scaler`	Scale video
`phrame_compositor`	Multi-layer composition
`phrame_overlay`	Overlay / graphics rendering
`phrame_dve_2d`	2D digital video effects
`phrame_audio_mixer`	Multi-channel audio mixing (party-line mode)
`phrame_package_maker`	Package / bundle streams

Each takes a JSON/YAML config validated against a schema (basic_config.yml is the base; per-component schemas extend it). A config names the instance, lists input[] (vdi://…), defines the output (video/audio/package), and sets video properties (pixel format, size, frame rate) plus an msg_config for MQTT.

Live control is the Lua layer: MQTT topics are bound to Lua scripts (actions[]), a shared registry holds state (base topic, stream id, alpha, …), and scripts call registry:get()/update() and mqtt_obj:queue_msg() to emit control messages — e.g. turning a UI button press into an .../OVERLAY/CMD command on the live overlay.

Under the hood

Language: C++17 (CMake). Links FFmpeg (libavutil/libswscale), libuuid, and the Phrame plugin API.
Frame-safe reconfiguration. phrame_mixer_connector.cpp is the core framework: runtime config updates use a double buffer (desired_config vs actual_config) guarded by mutexes and an atomic needs_update flag, so configuration can change without dropping frames.
Runtime plugins. Transports are loaded at runtime via the common plugin API (libvdi.so, libplugin-mxl.so, libphramendi.so, libplugin-hls.so, libplugin-null.so, …) — see Frame bus & plugins.
Control transport. MQTTClient.cpp (TLS/SSL); interface_factory.cpp loads the .so plugins; phrame_stats_publisher.cpp publishes stats.

Environment: BUILD_TYPE (Release/Debug/RelWithDebInfo), LOG_LVL.

Part of the Phrame documentation system — one Markdown source, four audiences, a code-generated house-style diagram.