Scenario Video Assembly

Overview

Scenario has no editing tools on the MCP surface. Every compositor, concatenator, trimmer and captioner is a deterministic model run through

model_run

. The compositor, concatenator and trimmer ids are fixed and named below; Scenario ships two captioners, so that one is discovered with

recommend

. Connection and the core loop: see the

scenario

skill; the clips themselves: see

scenario-video

. If a sibling skill named here is missing from your available skills, ask the user to install it (

npx skills add scenario-labs/skills --skill <name>

); unattended, proceed from tool schemas and flag the gap.

Quick reference: pick the backend first

Need	Model
Clips end to end, optional transitions	`model_scenario-video-concat`
Anything overlapping: overlay, bed, titles	`model_scenario-compose-video`
Still layout (thumbnails, sheets, key art)	`model_scenario-compose-image`

These ids are constants: each is Scenario's single deterministic tool for its operation, so discovery would only re-derive it.

Concat is sequential:

videos

takes 2 to 50 files (never 1),

preserveAudio

(default true) carries each clip's own track into the cut, and the optional

transitions

array's "length must be number of videos - 1". Each entry is an object

{type, duration}

, never a bare string:

type

is one of 18 names read off the schema (

fade

, the default, is the plain crossfade;

dissolve

is a different effect;

none

a hard cut) and

duration

runs 0.1 to 5 seconds, default 0.5. Omit the array for hard cuts throughout, the right call whenever the brief does not ask one shot to flow into the next.

preserveAudio

is not a guarantee of sync: a concatenated cut has come back with its audio drifting against the picture, with and without transitions (a confirmed defect at authoring time). A concat of clips carrying dialogue or effects is verified, never trusted:

asset_get

the output and compare

properties.duration

with the inputs' sum (each transition shortens the cut by up to its

duration

), then download it and check that the audio and video streams run the same length (a local probe of the download is inspection, not editing) and that a visible cue (a cut, a mouth opening, an impact) lands on its sound. When speech must stay locked to the picture, assemble in Video Studio instead: each clip layer carries its own track at its

startTime

, so a drift introduced by joining has nowhere to arise, at the price of hard cuts or per-layer fades in place of the transition set. Concat stays the tool for silent clips and for cuts whose bed is laid afterwards.

Video Studio is an absolute timeline:

layers

holds 1 to 50 image, video or audio sources placed by

startTime

and stacked by

zIndex

(higher in front), with per-layer

fadeIn

fadeOut

rather than a between-clip array, so a cross-fade between two clips belongs in concat. At least one layer must be a video, so a music bed over a still is rejected.

The Video Studio contract

Per layer, three timing ideas have confusable names:

```
startTime
```
and
```
endTime
```
place the layer on the timeline.
```
trimStart
```
and
```
trimEnd
```
are amounts shaved off the head and tail of the source, not in and out points: to play the first 20 seconds of a 90-second track, set
```
trimEnd: 70
```
.
```
duration
```
overrides the layer's length. The top-level
```
duration
```
is a different field, setting the whole composition, and applies only when
```
durationMode
```
is
```
"custom"
```
.

Everything is in seconds at

step: 0.1

, so do not promise frame-accurate cuts.

and

are strings taking pixels, percentages or words, and

anchor

says which point of the layer they address:

top-left

top-center

top-right

center-left

center

center-right

bottom-left

bottom-center

bottom-right

(the middle one is bare

center

), defaulting to

"top-left"

. A bottom-right logo is

x: "right"

y: "bottom"

anchor: "bottom-right"

, flush to the edge unless you inset it with a percentage.

canvasMode

and

durationMode

both default to

"auto"

, computed from the layers: a custom frame is

canvasMode: "custom"

plus numeric

canvasWidth

and

canvasHeight

(there are no top-level

width

height

, and unlike the layers' string

width

height

these are numbers), and a custom length is

durationMode: "custom"

plus the top-level

duration

fit

only acts on a layer that also sets the layer's own

width

and

height

, strings like

and

: to reframe a clip, set both to the canvas size as bare pixel numbers in strings (

width: "1920"

height: "1080"

, the form of the schema's own

"0"

default; a percent string also works) and pass

"cover"

(crops) or

"contain"

(letterboxes), since the default

"fill"

stretches. Give an overlay layer an explicit

width

and

height

even at its native size: leaving them empty is documented as preserving the original but does not reliably, and a 560x80 strip came back at 1792x256 on a 1920x1080 canvas. The output field is

videoOutputFormat

here,

imageOutputFormat

in Image Studio, and

outputFormat

in concat and the trim utilities.

A layer's

type

(image, video, audio, or mask) is optional and otherwise inferred from

source

. There is no text layer, so titles, lower thirds and end cards arrive as rendered PNGs composited as image layers;

scenario-text-overlay

renders them letter-perfect.

Worked example: three clips, a music bed, and captions

For every source,
```
asset_get
```
and read
```
properties
```
: the real
```
duration
```
(audio carries it too),
```
frameRate
```
on video, and
```
width
```
/
```
height
```
on video and images alike. A model asked for eight seconds does not always return exactly eight.

Add them up to get each clip's

startTime

, then

model_schema_get

model_scenario-compose-video

```
model_run
```
it with
```
layers
```
holding the three clips at their computed
```
startTime
```
s (
```
zIndex: 0
```
), a logo PNG pinned by
```
x
```
/
```
y
```
/
```
anchor
```
at
```
zIndex: 1
```
, and the music as an audio layer trimmed to the clips' total with
```
trimEnd
```
, since auto
```
durationMode
```
computes from every layer, the bed included.
```
volume
```
(0 to 2) and
```
mute
```
are per-layer and apply to video layers too, so balance the bed from either side. Set
```
canvasMode: "custom"
```
with
```
canvasWidth
```
and
```
canvasHeight
```
;
```
fps
```
defaults to 30 and takes whole numbers from 1 to 120, so set it to the clips' measured
```
frameRate
```
when they agree (rounded), which is what step 1 read it for.
```
jobs_wait
```
, then caption the finished cut rather than each clip:
```
model_scenario-caption-studio
```
(an authoring-time pick, since Scenario ships two captioners: re-discover with
```
recommend
```
) takes it as
```
video
```
and transcribes whatever audio the master actually carries, so lower the bed's
```
volume
```
rather than muting the dialogue. It burns captions in by default, takes an existing
```
.srt
```
as
```
subtitles
```
, a file input needing
```
upload_asset
```
first, returns a sidecar when
```
outputSrt
```
is true, and positions them with
```
textPosition
```
(
```
top
```
,
```
middle
```
or
```
bottom
```
, default
```
bottom
```
, so move it off a bottom-edge overlay).
```
asset_display
```
to review, then
```
asset_download
```
with
```
format
```
left unset (it is an image conversion target) for the file.

Trim, split and resize have their own tool models. Note

model_scenario-video-cut

startTime

endTime

are source in and out points, not timeline placement.

Common mistakes

Reaching for an MCP tool like
```
video_compose
```
, or for local ffmpeg to do the edit itself. The editing surface is
```
model_run
```
on tool models; probing a download is fine.
Handing concat one clip, or one transition per clip: the minimum is 2 videos, and transitions run one fewer.
Trusting
```
dry_run
```
here as validation: it returns a cost estimate only, and assembly payloads are the most structurally complex in the catalog.
Captioning a concatenated master before checking its sync: the captioner times its lines to the audio it hears, so drifted audio ships drifted captions on top of it.

scenario-video-assembly

NPX Install

Tags

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