Rendering Shorts

reeln’s render commands transform landscape clips into portrait (9:16) or square (1:1) short-form video — ready for Instagram Reels, TikTok, YouTube Shorts, etc.

Basic render

reeln render short clip.mkv

This produces a 1080x1920 vertical video using the default pad framing mode.

If you have paths.source_dir configured, you can omit the clip path — reeln auto-discovers the most recent replay:

reeln render short

Quick preview

Generate a fast, low-resolution preview before committing to a full render:

reeln render preview clip.mkv

Preview accepts all the same options as render short.

Framing modes

Pad (default)

Scales the source to fit the width, then adds bars top and bottom. The full frame is visible but letterboxed.

reeln render short clip.mkv --crop pad

Crop

Scales the source to fill the height, then trims the sides. The frame is fully filled but edges are lost.

reeln render short clip.mkv --crop crop

Anchor

Control where the crop window is positioned:

# Center (default)
reeln render short clip.mkv --crop crop --anchor center

# Follow the left side of the frame
reeln render short clip.mkv --crop crop --anchor left

# Custom position (x,y from 0.0 to 1.0)
reeln render short clip.mkv --crop crop --anchor 0.3,0.5

Output formats

# Vertical — 1080x1920 (default)
reeln render short clip.mkv --format vertical

# Square — 1080x1080
reeln render short clip.mkv --format square

# Custom size
reeln render short clip.mkv --size 720x1280

Speed

# Half speed (slow motion)
reeln render short clip.mkv --speed 0.5

# Double speed
reeln render short clip.mkv --speed 2.0

Scale / zoom

Zoom into the content before framing:

# 1.5x zoom with crop — tighter on the action
reeln render short clip.mkv --crop crop --scale 1.5

# 2x zoom with pad — zoomed in, remaining space padded
reeln render short clip.mkv --crop pad --scale 2.0

Color grading

Apply a LUT (Look-Up Table) for color grading:

reeln render short clip.mkv --lut warm.cube

LUT files (.cube or .3dl) are standard color grading files supported by most video tools.

Subtitle overlays

Overlay an ASS subtitle file:

reeln render short clip.mkv --subtitle overlay.ass

Pad color

Change the letterbox bar color (pad mode only):

reeln render short clip.mkv --crop pad --pad-color "#1a1a1a"

Combining options

Options compose freely:

reeln render short clip.mkv \
  --crop crop \
  --scale 1.3 \
  --speed 0.5 \
  --lut cinematic.cube \
  --format vertical

Render within a game context

When you provide a game directory, renders are tracked in game.json:

reeln render short clip.mkv --game-dir .
reeln render short clip.mkv --game-dir . --event abc123

Dry run

Preview the render plan without producing output:

reeln render short clip.mkv --crop crop --speed 0.5 --dry-run

Debug mode

See the full ffmpeg command and filter chain:

reeln render short clip.mkv --debug

This writes debug artifacts to debug/ including the ffmpeg command, filter graph, and input/output metadata.

Next steps