Evals / audio / Cut and join

Remove the silences

Remove the long silent parts from pauses.mp3 and save it as tight.mp3.

normalsingledeft audio remove-silence

The task

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

deft audio remove-silence pauses.mp3 --min-silence 1 -o tight.mp3

Input

pauses.mp3 61.6 KB · mp3, 15.7s

Reference output

tight.mp3 81.8 KB · mp3, 11.6s
How a result is judged (1 check)
  • format: file = "tight.mp3", format = "mp3"

Runs

CodexWithout deftPassed2026-11-07

Time
19s
New tokens
4.9k
Total input
55.2k
Output tokens
0.6k
Commands
3
Failed
0

Trace

  1. I’ll inspect the audio file and available audio tools, then create `tight.mp3` in the current directory with long pauses removed.

  2. pwd && rg --files -g 'pauses.mp3' -g 'AGENTS.md' -g 'SKILL.md' && command -v ffmpeg || true && command -v sox || true
    output
    pauses.mp3
/opt/homebrew/bin/ffmpeg
  3. ffprobe -v error -show_entries format=duration:stream=sample_rate,channels -of default=noprint_wrappers=1 pauses.mp3 && ffmpeg -hide_banner -i pauses.mp3 -af silencedetect=noise=-40dB:d=0.8 -f null -
    output
    sample_rate=22050
channels=1
duration=15.725714
Input #0, mp3, from 'pauses.mp3':
  Metadata:
    encoder         : Lavf61.7.100
  Duration: 00:00:15.73, start: 0.050113, bitrate: 32 kb/s
  Stream #0:0: Audio: mp3 (mp3float), 22050 Hz, mono, fltp, 32 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (mp3 (mp3float) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, null, to 'pipe:':
  Metadata:
    encoder         : Lavf61.7.100
  Stream #0:0: Audio: pcm_s16le, 22050 Hz, mono, s16, 352 kb/s
      Metadata:
        encoder         : Lavc61.19.101 pcm_s16le
[silencedetect @ 0xc0c8243c0] silence_start: 3.168209
[silencedetect @ 0xc0c8243c0] silence_end: 6.221315 | silence_duration: 3.053107
[silencedetect @ 0xc0c8243c0] silence_start: 9.371247
[silencedetect @ 0xc0c8243c0] silence_end: 12.437868 | silence_duration: 3.066621
[out#0/null @ 0xc0c820180] video:0KiB audio:674KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: unknown
size=N/A time=00:00:15.64 bitrate=N/A speed=1.95e+03x

  4. The file has two roughly 3 second silent gaps. I’m trimming those while leaving a short pause at each cut, then I’ll confirm the output file was written.

  5. ffmpeg -hide_banner -y -i pauses.mp3 -af "silenceremove=stop_periods=-1:stop_duration=0.8:stop_threshold=-40dB:stop_silence=0.15" -codec:a libmp3lame -q:a 2 tight.mp3 && ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1 tight.mp3
    output
    Input #0, mp3, from 'pauses.mp3':
  Metadata:
    encoder         : Lavf61.7.100
  Duration: 00:00:15.73, start: 0.050113, bitrate: 32 kb/s
  Stream #0:0: Audio: mp3 (mp3float), 22050 Hz, mono, fltp, 32 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (mp3 (mp3float) -> mp3 (libmp3lame))
Press [q] to stop, [?] for help
Output #0, mp3, to 'tight.mp3':
  Metadata:
    TSSE            : Lavf61.7.100
  Stream #0:0: Audio: mp3, 22050 Hz, mono, fltp
      Metadata:
        encoder         : Lavc61.19.101 libmp3lame
[out#0/mp3 @ 0xb7542c180] video:0KiB audio:71KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: 0.310644%
size=      71KiB time=00:00:11.42 bitrate=  51.1kbits/s speed= 477x    
duration=11.493878

  6. Created `tight.mp3` in the current directory. It’s about 11.5 seconds long, with the two roughly 3-second silent gaps trimmed.

Output

tight.mp3 71.3 KB · mp3, 11.5s

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

Time
13s
New tokens
5.3k
Total input
73.0k
Output tokens
0.3k
Commands
4
Failed
0

Trace

  1. I’ll inspect the audio and available local tools, then trim the silent sections and save `tight.mp3` in the current directory.

  2. cat .agents/skills/deft/SKILL.md
    output
    ---
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; r
… 700 more characters
  3. deft find "remove long silent parts from audio" && ls -l pauses.mp3
    output
    audio remove-silence  audio -> audio  Cut silent parts: --threshold -40 --min-silence 0.5
-rw-r--r--@ 1 user  staff  63129 Nov  5 21:51 pauses.mp3
  4. deft audio remove-silence --help
    output
    deft audio remove-silence - Cut silent parts: --threshold -40 --min-silence 0.5

Usage: deft audio remove-silence <audio>... [-o <audio|dir>] [options]
In: audio (each handled separately)   Out: audio (default <name>.nosilence.<ext>)
--edges-only trims the start and end and leaves pauses alone.

Options:
  --threshold <number>         Quieter than this many dB counts as silence (default -40)
  --min-silence <time>         Shortest silence to cut (default 0.5)
  --edges-only                 Only trim the start and end
Common: -o --force --dry-run --json -j   (deft help common)

Examples:
  deft audio remove-silence gaps.wav -o tight.wav

Result fields: removed_seconds
Needs: ffmpeg, ffprobe
  5. deft audio remove-silence pauses.mp3 -o tight.mp3 --threshold -40 --min-silence 0.5
    output
    ok audio.remove-silence pauses.mp3 -> tight.mp3  5.1s removed  0.22s

  6. Done. I removed 5.1 seconds of silence from `pauses.mp3` and saved the result as [tight.mp3](tight.mp3).

Output

tight.mp3 80.6 KB · mp3, 10.6s

Claude Opus 5.5Without deftPassed2026-11-07

Time
17s
New tokens
9.8k
Total input
57.3k
Output tokens
0.8k
Commands
0
Failed
0

Trace

    Output

    tight.mp3 43.9 KB · mp3, 11.2s

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

    Time
    16s
    New tokens
    10.7k
    Total input
    75.5k
    Output tokens
    0.7k
    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
      tight.mp3 81.8 KB · mp3, 11.6s

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