frames/skills/media-use/references/operations.md

Media operations: agent guidance

media-use resolves and remembers assets. For operating on them: cutting, reframing, stitching, transforming, it does not wrap every action as a bespoke command. Instead it points you at the right local tool (decision OP1). Run the tool, then register the output with resolve --from <output> --type <type> so the result lands in the ledger and the global cache like any other asset.

All tools below are local and free. ffmpeg is assumed present (it backs the engine already).

Cut / trim: keep a slice

ffmpeg -i in.mp4 -ss 00:00:12 -to 00:00:20 -c copy out.mp4   # 0:12–0:20, no re-encode

In-composition trimming usually needs no new file: a clip plays a sub-window via data-media-start + data-duration (see frames-core). Only cut a physical file when exporting/assembling outside the composition.

Reframe / crop: change aspect ratio

# 16:9 -> 9:16, crop centered
ffmpeg -i in.mp4 -vf "crop=ih*9/16:ih,scale=1080:1920" out.mp4

For a non-destructive crop, set a clip-path on the element in the composition itself (render-time, source file untouched) instead of re-encoding with ffmpeg.

Montage / stitch: join clips

printf "file '%s'\n" a.mp4 b.mp4 c.mp4 > list.txt
ffmpeg -f concat -safe 0 -i list.txt -c copy out.mp4

Silence-cut / highlight: trim dead air, grab the best moment

auto-editor in.mp4 --edit audio:threshold=4% -o tight.mp4   # pip install auto-editor
scenedetect -i in.mp4 detect-adaptive list-scenes           # pip install scenedetect

Transforms that run on this machine (process)

Op	Command
Background removal	frames remove-background in.png (u2net)
Upscale	realesrgan-ncnn-vulkan -i in.png -o out.png -s 4

After any op: resolve --from out.ext --type <type> to register the derived asset (it records provenance and auto-promotes to the global cache).

media-use does not re-wrap ffmpeg here, and that is deliberate (OP1). The value it adds is the ledger + global reuse on the output, via --from. Add a thin process verb only if agents repeatedly fumble these recipes.

Exact error-diffusion dither

Use the local processor when the requested look specifically calls for Floyd-Steinberg, Atkinson/Macintosh, Jarvis-Judice-Ninke, Stucki, Burkes, or a Sierra variant. These are sequential error-diffusion algorithms, not the realtime Bayer effects.dither shader.

node <SKILL_DIR>/scripts/dither.mjs \
  --input source.mp4 \
  --out source.atkinson.mp4 \
  --algorithm atkinson \
  --palette '#0f380f,#306230,#8bac0f,#9bbc0f' \
  --point-size 3

node <SKILL_DIR>/scripts/resolve.mjs \
  --from source.atkinson.mp4 --type video --project .

Available algorithms: floyd-steinberg, atkinson, jarvis-judice-ninke, stucki, burkes, sierra, sierra-lite, and two-row-sierra. The default is balanced Floyd-Steinberg with a black/white palette. Palettes contain 2-6 #rrggbb colors in authored dark-to-light order; reversing the order intentionally inverts the mapping. --point-size controls 1-20px blocks; --brightness and --contrast accept 0.5-2; --detail accepts 0.1-1.

The processor supports ordinary SDR images and MP4 video, preserves video audio, and emits BT.709 MP4. It rejects tagged PQ/HLG input rather than silently tone-mapping it. To animate the transformation, keep the original and processed files as two real media layers and use the seek-safe GSAP timeline to reveal or crossfade between them. Use the realtime Bayer shader instead when the dither amount itself must animate continuously.

Transcription

transcribe.mjs is the one transcription path: POST /v1/audio/transcriptions through api.hanzo.ai. It emits { text, words: [{text,start,end}] }, feeding transcript-cut, captions, and the audio engine directly.

node <SKILL_DIR>/scripts/transcribe.mjs --input talk.mp4 --out talk.transcribe.json
node <SKILL_DIR>/scripts/transcribe.mjs --input talk.mp4 --lang es

--model selects whisper (default) or the smaller, faster whisper-small. Nothing is downloaded and nothing is built on first use.

words is empty when the service returns text without per-word timings, and the command says so. Timings are never interpolated: a cut made on invented word boundaries reads as correct and drifts against the audio. A caller that needs per-word cuts should treat an empty words as "fall back to line timing".

Text-based editing (transcript cut)

transcript-cut.mjs is a compiler, not a wrapper: it turns word timestamps and agent cut decisions into exact kept segments. It is provided even though the rest of this file is guidance-only.

node <SKILL_DIR>/scripts/transcript-cut.mjs \
  --input talk.mp4 \
  --transcript talk.transcribe.json \
  --remove "12.41-15.02,88.3-91.7" \
  --remove-fillers "um,uh,like" \
  --cut-silence 0.8 \
  --out talk.cut.mp4

resolve --from talk.cut.mp4 --type video

Use --plan first when you want to inspect the kept segment JSON before encoding.

Ducking (declare in-composition / bake for export)

B1, declare ducking in the composition. audio-duck.mjs emits GSAP volume keyframes. Paste them into the composition timeline, the source file stays untouched.

node <SKILL_DIR>/scripts/audio-duck.mjs \
  --meta audio_meta.json \
  --target "#bgm" \
  --composition index.html

// auto-duck: #bgm under narration (generated; base volume 0.6)
tl.to("#bgm", { volume: 0.15, duration: 0.15 }, 3.42);
tl.to("#bgm", { volume: 0.6, duration: 0.4 }, 9.87);

B2, bake ducking only for exported or standalone files.

ffmpeg -i bgm.mp3 -i voice.wav \
  -filter_complex "[0][1]sidechaincompress=threshold=0.03:ratio=8:attack=200:release=400[ducked]" \
  -map "[ducked]" bgm.ducked.wav

Declare inside compositions. Bake only for assets leaving the frames pipeline.

Publish loudness

Two-pass loudnorm measures first, then applies the measured values with the target LUFS baked in.

Socials target, -14 LUFS:

ffmpeg -i mix.wav \
  -af loudnorm=I=-14:TP=-1.5:LRA=11:print_format=json \
  -f null -

ffmpeg -i mix.wav \
  -af loudnorm=I=-14:TP=-1.5:LRA=11:measured_I=<input_i>:measured_TP=<input_tp>:measured_LRA=<input_lra>:measured_thresh=<input_thresh>:offset=<target_offset>:linear=true:print_format=summary \
  mix.social.wav

Podcast target, -16 LUFS:

ffmpeg -i mix.wav \
  -af loudnorm=I=-16:TP=-1.5:LRA=11:print_format=json \
  -f null -

ffmpeg -i mix.wav \
  -af loudnorm=I=-16:TP=-1.5:LRA=11:measured_I=<input_i>:measured_TP=<input_tp>:measured_LRA=<input_lra>:measured_thresh=<input_thresh>:offset=<target_offset>:linear=true:print_format=summary \
  mix.podcast.wav

Generate: images

resolve --type image looks in the shared catalog first (media/image/); on a miss it generates through POST /v1/images/generations. Both rungs are one credential and one host — nothing to install, no model to cache, no RAM ladder to satisfy.

To skip the shelf and go straight to generation, pass --provider hanzo; to stay on the shelf, --provider catalog. --local-only skips both and leaves the project and global caches.

The catalog is empty until it is stocked. An empty prefix is reported as such and image falls through to generation.

Generate: video

resolve --type video "<intent>" generates through POST /v1/videos/generations and freezes the result into the project ledger. Pass --voice-id when the piece speaks and the default voice is wrong.

There is no catalog rung for video: a clip is made for the piece it is in, and a shelf of generic clips is a worse answer than a fresh one. Under --local-only there is no video rung at all, which resolve reports as a clean miss rather than a silent skip.

HEVC / H.265 sources

HEVC/H.265 sources need no conversion for render (FFmpeg pre-decodes all input video) or for preview (auto-proxy transcodes and caches an H.264 copy on first use, disable with --no-proxy or media.autoProxy: false in frames.json). A manual H.264 proxy via ffmpeg -i in.mp4 -c:v libx264 -crf 18 proxy.mp4, registered with resolve --from, remains available for edge cases (e.g. auto-proxy disabled, or ffmpeg unavailable at preview time).