Evals / video / Sound track

Add a soundtrack

Replace the sound of movie.mp4 with music.mp3 and save it as scored.mp4.

normalsingledeft video add-audio

The task

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

deft video add-audio movie.mp4 --audio music.mp3 -o scored.mp4

Input

movie.mp4 1.1 MB · h264 1280x720, aac, 10.0s
music.mp3 96.2 KB · mp3, 6.1s

Reference output

scored.mp4 1.0 MB · h264 1280x720, aac, 10.0s
How a result is judged (1 check)
  • media: file = "scored.mp4", has_audio = true, has_video = true

Runs

CodexWithout deftPassed2026-11-07

Time
10s
New tokens
6.9k
Total input
41.5k
Output tokens
0.3k
Commands
2
Failed
0

Trace

  1. I’ll inspect the two media files and available tools, then mux the music onto the movie and save `scored.mp4` here.

  2. rg --files -g 'movie.mp4' -g 'music.mp3' -g 'AGENTS.md' -g 'scored.mp4'
    output
    movie.mp4
music.mp3
  3. command -v ffmpeg && ffmpeg -y -i movie.mp4 -i music.mp3 -map 0:v:0 -map 1:a:0 -c:v copy -c:a aac -shortest scored.mp4
    output
    /opt/homebrew/bin/ffmpeg
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.  3.10
… 2528 more characters

  4. Done. I replaced the movie’s audio with `music.mp3` and saved the result as [scored.mp4](scored.mp4). The music is shorter than the video, so the output ends when the music ends.

Output

scored.mp4 654.0 KB · h264 1280x720, aac, 6.1s

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

Time
16s
New tokens
8.5k
Total input
57.7k
Output tokens
0.6k
Commands
3
Failed
0

Trace

  1. I’ll check the available media instructions and files, then replace the video’s audio and save `scored.mp4` in this directory.

  2. cat .agents/skills/deft/SKILL.md 2>/dev/null || cat .codex/skills/deft/SKILL.md 2>/dev/null || cat .codex/skills/.system/deft/SKILL.md 2>/dev/null; rg --files -g 'movie.mp4' -g 'music.mp3' -g 'AGENTS.md' -g 'SKILL.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
… 752 more characters
  3. deft video
    output
    deft video - commands (input -> output)
  info               video -> report      Duration, size, frame rate, codecs
  add-audio          video -> video       Replace or mix the soundtrack: --audio song.mp3
  add-subtitles      video -> video       Add subtitles: burned into the picture, or --soft
  chunk              video -> video...    Cut into equal parts: --length 10:00
  compress           video -> mp4         Smaller file: --level, --target-size, --max-height
  convert            video|gif -> video   Change container and codec: --to mp4|webm|mov|mkv
  crop               video -> video       Cut a region: --box or --aspect 1:1
  download           url -> video         Save a video: --resolution 720p, --to mp4|webm|mkv [net]
  extract-audio      video -> audio       Save the soundtrack: --to mp3|m4a|wav|flac|ogg
  extract-subtitles  video -> srt|vtt     Save an embedded subtitle track: --to srt|vtt
  fade               video -> video       Fade: --fade-in 1 --fade-out 2
  frames             video -> png|jpg...  Save frames as images: --fps 1 or --at 0:05,0:10
  from-images        image... -> video    Slideshow: --duration, --fps, --audio
  merge              video... -> mp4      Join videos; --transition fades
  mute               video -> video       Remove the audio track
  pad                video -> video       Fit into a frame with bars: --size 1080x1920
  repeat             video -> video       Repeat a video: --count 3 plays it three times
  resize             vid
… 891 more characters
  4. deft video add-audio movie.mp4 -o scored.mp4 --audio music.mp3
    output
    ok video.add-audio movie.mp4 -> scored.mp4  1.0MB  0.26s

  5. Done. I replaced the soundtrack in `movie.mp4` with `music.mp3` and saved the result as [scored.mp4](scored.mp4).

Output

scored.mp4 1.0 MB · h264 1280x720, aac, 10.0s

Claude Opus 5.5Without deftPassed2026-11-07

Time
16s
New tokens
9.4k
Total input
42.5k
Output tokens
0.8k
Commands
0
Failed
0

Trace

    Output

    scored.mp4 1.2 MB · h264 1280x720, aac, 10.0s

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

    Time
    19s
    New tokens
    10.1k
    Total input
    74.7k
    Output tokens
    0.5k
    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
      scored.mp4 1.0 MB · h264 1280x720, aac, 10.0s

      Claude CodeWithout deftNot run yet

      Claude CodeWith deftNot run yet