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Video compositing via FFmpeg, wrapped in clean R functions.
compost turns common ffmpeg
filter_complex patterns (overlay, chromakey, concat, scale,
stack) into small, composable R functions, and lowers an OpenTimelineIO
timeline (through rotio) to a single
rendered video.
Every function shells out to
ffmpeg/ffprobe. Nothing is reimplemented in R;
the package’s job is to build correct filtergraphs so you don’t have
to.
remotes::install_github("cornball-ai/compost")Requires ffmpeg (>= 5.0) on your PATH.
The only R dependency is rotio.
A few patterns hold across the API:
overwrite = TRUE (default) passes -y to
ffmpeg.dry_run = TRUE returns the ffmpeg command string
instead of running it, so you can inspect or test the filtergraph
without rendering.| Function | Does |
|---|---|
overlay() |
Composite a PNG (with alpha) or video over a background |
pip() |
Picture-in-picture a clip into a corner |
chromakey() |
Key out a colored background and composite |
colorkey() |
Key out a flat background, write ProRes 4444 (alpha preserved) |
hstack() |
Stack two videos side by side |
vstack() |
Stack two videos vertically |
pad() |
Scale to fit and pad onto a canvas |
zoom() |
Stepped zoom that changes level at STT line boundaries |
compose_layout() |
Paint N streams into pixel-rect slots on a canvas (heads over slides, stacks, over-shoulder boxes) |
| Function | Does |
|---|---|
still_clip() |
One image → a video clip, static or Ken Burns pan/zoom |
frames_clip() |
A numbered frame sequence → a video clip |
| Function | Does |
|---|---|
concat() |
Join segments sequentially via the concat demuxer |
crossfade_concat() |
Dissolve between clips, optionally overlay one audio track |
| Function | Does |
|---|---|
audio_convert() |
Re-encode / resample / remix to a new container or codec |
audio_concat() |
Join audio files with exact silence gaps (decoded-domain, one encode) |
normalize_audio() |
Single EBU R128 loudnorm pass |
broadcast_audio() |
Broadcast-clean chain: high-pass, de-hum, loudness, fades |
align_audio() |
Locate a clip’s audio within a longer narration |
align_overlaps() |
Place chunks on the narration clock and derive overlaps |
subclip() |
Cut a [start, end] range out of a media file |
rms_curve() |
Per-block RMS levels across a file |
| Function | Does |
|---|---|
probe() |
Query video properties via ffprobe |
frame_export() |
Pull a single frame at a given time as an image |
| Function | Does |
|---|---|
render_timeline() |
Lower a rotio (OTIO) timeline to a rendered video: source-range
trims, dissolve transitions, still/sequence pre-render,
cornball.* motion effects, multi-track slot layouts,
caption burn, and a narration bed the video locks to |
The cornball.* effect namespace and the slot-layout
contract are documented in inst/schema/cornball-effects.md
and inst/schema/cornball-layout.md.
Picture-in-picture a webcam into the bottom-right of a screen recording:
library(compost)
pip("screen.mp4", "webcam.mp4", "out.mp4",
scale = 0.25, corner = "lower-right")Convert a meeting recording to STT-ready audio in one pass:
audio_convert("recording.mp4", "speech.wav",
sample_rate = 16000, channels = 1)Crossfade a sequence of clips and lay one music bed over the top:
crossfade_concat(c("a.mp4", "b.mp4", "c.mp4"), "reel.mp4",
fade = 0.5, audio = "music.mp3")Inspect the ffmpeg command without rendering (returns the command string):
overlay("bg.mp4", "logo.png", "out.mp4", x = 40, y = 40, dry_run = TRUE)MIT. Copyright cornball.ai.
These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.