Transitions

A Showmesh transition changes a parameter over time. Common parameters are video opacity, audio volume, and pan.

Anatomy of a transition

A Transition action contains:

• Property — parameter to change;
• From — optional starting value;
• To — destination value;
• Duration — change duration in milliseconds;
• Delay — delay after the trigger;
• Curve — shape of the value change;
• Trigger — when the action starts.

If From is omitted, the engine reads the parameter's current value when the action fires. This is the right choice for interruptible or reversible fades.

Curves

Curve	Character
Linear	Constant mathematical rate
Ease In	Slow start
Ease Out	Slow finish
S Curve / Ease In Out	Soft start and finish
Step Start	Jumps at the beginning
Step End / Hold Then Step	Holds and jumps at the end

Volume uses perceptual mapping and pan uses equal-power mapping. A linear raw value therefore does not necessarily produce a linear perceived audio change.

Fade-in and fade-out

Action	Trigger	From	To
Opacity fade-in	On Play	0	1
Opacity fade-out	On Cue Stop	—	0

For a video with audio, usually add the same pair for Volume.

Crossfade between two videos

1. Put Video A on layer 0 and Video B on layer 1.
2. Add Video B opacity 0 → 1 with On Play.
3. Add another action on Video B that targets Video A and fades opacity to 0 with On Cue Start.
4. Add an At Time or On Finished Stop command for Video A.

Equal durations produce a conventional crossfade. Fade Video A's volume too if it contains audio.

Legacy transition data

Older projects may contain tracks[], fadeInSec, fadeOutSec, or single- parameter transition fields. The engine migrates most of these to actions. Tracks with relative destinations may remain on the legacy execution path.

Do not hand-edit migrated JSON casually

Save old projects under a new name and inspect the cue list. Actions are the new source of truth; mixing old and new fields by hand makes a show difficult to audit.