Speed up a clip

Make bunny.mp4 play twice as fast and save it as fast.mp4.

The task

The reference answer shows the job can be done with deft. It is not an agent run.

deft video speed bunny.mp4 --factor 2 -o fast.mp4

Input

bunny.mp4 946.5 KB · h264 1280x720, 10.0s

Reference output

fast.mp4 1.3 MB · h264 1280x720, 5.0s

How a result is judged (1 check)

python: code = "import subprocess; d = lambda f: float(subprocess.check_output(['ffprobe', '-v', 'error', '-show_entries', 'format=duration', '-of', 'csv=p=0', f])); assert abs(d('fast.mp4') * 2 - d('bunny.mp4')) < 1"

Runs

CodexWithout deftPassed2026-11-07

Time: 12s
New tokens: 5.1k
Total input: 42.0k
Output tokens: 0.3k
Commands: 2
Failed: 0

Trace

I’ll check the video and available media tools, then write `fast.mp4` in the current directory at 2× speed.

ls -l bunny.mp4 && command -v ffmpeg

output

-rw-r--r--@ 1 user  staff  969201 Nov  5 21:11 bunny.mp4
/opt/homebrew/bin/ffmpeg

ffmpeg -y -i bunny.mp4 -filter:v "setpts=0.5*PTS" -filter:a "atempo=2.0" -c:v libx264 -preset medium -crf 18 -c:a aac -b:a 192k fast.mp4

output

ffmpeg version 7.1.1 Copyright (c) 2000-2025 the FFmpeg developers
  built with Apple clang version 15.0.0 (clang-1500.1.0.2.5)
  configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/7.1.1_1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags='-Wl,-ld_classic' --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d --enable-libharfbuzz --enable-libjxl --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-audiotoolbox --enable-neon
  libavutil      59. 39.100 / 59. 39.100
  libavcodec     61. 19.101 / 61. 19.101
  libavformat    61.  7.100 / 61.  7.100
  libavdevice    61.  3.100 / 61.  3.100
  libavfilter    10.  4.100 / 10.  4.100
  libswscale      8.  3.100 /  8.  3.100
  libswresample   5.  3.100 /  5.  3.100
  libpostproc    58.  3.100 / 58.  3.100
Input #0, mov,mp4,m4a,3
… 4693 more characters

Created [fast.mp4](fast.mp4) at 2× speed.

Output

fast.mp4 3.3 MB · h264 1280x720, 5.0s

CodexWith deft, skill installedPassedRead the skillUsed deft2026-11-07

Time: 17s
New tokens: 4.7k
Total input: 56.5k
Output tokens: 0.4k
Commands: 3
Failed: 0

Trace

I’ll check the available video conversion workflow and process `bunny.mp4` into `fast.mp4` in this directory.

cat .agents/skills/deft/SKILL.md && rg --files -g 'bunny.mp4' -g 'AGENTS.md'

output

---
name: deft
description: "Use deft instead of writing a script for file jobs: PDF merge/split/compress/watermark, image resize/convert/compress, video and audio trim/convert/compress, spreadsheets, Markdown to PDF/HTML, and YouTube downloads and subtitles."
---

# deft

One local command for file jobs. Prefer it over writing Python or shell scripts.

Syntax: `deft <group> <command> [inputs] [-o output] [--options]`

Groups:
- `pdf`: Merge, split, compress, encrypt, forms, OCR, compare, convert
- `image`: Resize, crop, convert, compress, filters, montage, OCR
- `video`: Trim, crop, speed, convert, compress, GIF, frames (ffmpeg)
- `audio`: Convert, trim, merge, fade, speed, tag, normalize (ffmpeg)
- `doc`: Word/ODT/RTF: to text, Markdown, HTML, PDF; find and replace
- `slides`: PowerPoint: extract text, Markdown outline, PDF handout
- `data`: JSON/YAML/TOML/XML: convert, query with jq syntax, merge, diff
- `sheet`: Excel/CSV/ODS tables: filter, sort, join, pivot, convert
- `md`: Markdown to PDF, HTML, Word, EPUB; table of contents
- `html`: HTML to Markdown, text, Word, PDF; screenshots
- `epub`: E-books: info, to text, Markdown and PDF
- `email`: EML files: headers, text, attachments
- `contact`: VCF address books: to and from CSV
- `calendar`: ICS calendars: to and from CSV
- `gps`: GPX and KML tracks: convert, distance and time
- `youtube`: Info, download, audio, subtitles, thumbnail (yt-dlp)
- `file`: Any file: hash, duplicates, batch rename, base64, encoding
- `qr`: Cre
… 738 more characters

deft video speed --help

output

deft video speed - Speed up or slow down: --factor 2 or --factor 0.5

Usage: deft video speed <video>... [-o <video|dir>] [options]
In: video (each handled separately)   Out: video (default <name>.speed.<ext>)
Sound keeps its pitch.

Options:
  --factor <number>            2 is twice as fast, 0.5 half as fast (required)
Common: -o --force --dry-run --json -j   (deft help common)

Examples:
  deft video speed clip.mp4 --factor 2 -o fast.mp4
Needs: ffmpeg, ffprobe

deft video speed bunny.mp4 --factor 2 -o fast.mp4
output
```
ok video.speed bunny.mp4 -> fast.mp4  1.3MB  0.69s
```
Done. `bunny.mp4` now plays twice as fast in [fast.mp4](fast.mp4).

Output

fast.mp4 1.3 MB · h264 1280x720, 5.0s

Claude Opus 5.5Without deftPassed2026-11-07

Time: 16s
New tokens: 8.9k
Total input: 42.2k
Output tokens: 0.5k
Commands: 0
Failed: 0

Trace

Output

fast.mp4 1.6 MB · h264 1280x720, 5.0s

Claude Opus 5.5With deft, skill installedPassedRead the skillUsed deft2026-11-07

Time: 17s
New tokens: 9.8k
Total input: 59.2k
Output tokens: 0.4k
Commands: 0
Failed: 0

Trace

Output

.claude/skills/deft/SKILL.md 2.1 KB

---
name: deft
description: "Use deft first for any simple, direct operation on local files, whatever the type: convert, read, extract, edit, compress, merge, split, compare or inspect. Try it before writing a script or one-liner. If unsure, run deft find; if it says no command does this, use another tool. Not for programming work: to read, write or change source code, skip it."
---

# deft

One local command for file jobs. Prefer it over writing Python or shell scripts.

Syntax: `deft <group> <command> [inputs] [-o output] [--options]`

Groups:
- `pdf`: Merge, split, compress, encrypt, forms, OCR, compare, convert
- `image`: Resize, crop, convert, compress, adjust, montage, OCR
- `video`: Trim, merge, convert, compress, subtitles, GIF, frames (ffmpeg)
- `audio`: Convert, trim, normalize, denoise, cut silence (ffmpeg)
- `doc`: Word/ODT/RTF: to text, Markdown, HTML, PDF; find and replace
- `slides`: PowerPoint: extract text, Markdown outline
- `sheet`: Excel/CSV/ODS tables: SQL query, pivot, merge, split, convert
- `json`: JSON: convert, format, merge, diff, validate
- `toml`: TOML: convert, format, merge, diff, validate
- `xml`: XML: convert, format, merge, diff, validate
- `yaml`: YAML: convert, format, merge, diff, validate
- `md`: Markdown to PDF, HTML, Word, EPUB; table of contents
- `html`: HTML to Markdown, text, Word and PDF
- `epub`: E-books: info, to text, Markdown and PDF
- `gps`: GPX and KML tracks: convert, distance and time
- `qr`: Create QR codes and barcodes; read QR codes

How to use it:
1. Run `deft <group>` to list commands, or `deft find "<what you want>"` to search. If it says `no command does this`, use another tool.
2. Run `deft <group> <command> --help` for options and examples.
3. `deft convert <in> -o <out.ext>` converts between formats by extension.
4. Results are one line starting with `ok`, `partial` or `error`; add `--json` to parse them. Errors include a `hint:` with the fix.

Inputs are never overwritten; pass `--force` or `--in-place` to allow it. Globs and directories work as inputs; several inputs run in parallel.

If `deft` is not installed, ask the user, then follow https://github.com/firstprayer/deft/blob/main/docs/INSTALL.md

fast.mp4 1.3 MB · h264 1280x720, 5.0s

Claude CodeWithout deftNot run yet

Claude CodeWith deftNot run yet