Ffmpeg Mixing

What it does

When your agent uses it

• Stitching generated clips into an original video
• Inserting scenes at timestamps
• Any ffmpeg filtercomplex work involving trim/concat with a continuous audio track

Example prompts

• “/ffmpeg-mixing”

Requirements

• Compatibility (from SKILL.md): Requires ffmpeg installed locally.
• Pre-approved tools (allowed-tools): Bash(ffmpeg:*), Bash(ffprobe:*), Read

Workflow steps

5 steps, taken from the first numbered list in SKILL.md.

1. 1absolute timestamps: trim from full input file, not pre-trimmed
2. 2separate audio handling: use atrim on audio stream independently
3. 3setpts reset: always use setpts=PTS-STARTPTS after trim to reset timestamps
4. 4scale before trim: when mixing different resolutions, scale first then trim
5. 5video duration = audio duration: ensure total video segments match audio segment length

What it can do on your machine

Read from SKILL.md and the folder at commit da4face. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Bash(ffmpeg:*)
  • Bash(ffprobe:*)
  • Read

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • ffmpeg

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

• Compatibility

  Requires ffmpeg installed locally.

  From compatibility in the SKILL.md frontmatter.

Context cost

Ffmpeg Mixing loads about 676 tokens when it runs. Until then it costs about 68 tokens; SKILL.md has 151 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~68

When it runs · the whole SKILL.md, loaded when a task matches

~676

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from vargHQ/sdk at commit da4face, republished under its MIT licence (© vargHQ). 151 words, ~676 tokens.

name

ffmpeg-mixing

description

Mix, trim, and concatenate video clips with ffmpeg without audio/video desync. Use when stitching generated clips into an original video, inserting scenes at timestamps, or any ffmpeg filter_complex work involving trim/concat with a continuous audio track.

allowed-tools

Bash(ffmpeg:*), Bash(ffprobe:*), Read

compatibility

Requires ffmpeg installed locally.

license

MIT

metadata.author

vargHQ

metadata.version

1.0.0

# BAD: relative timestamps after pre-trim
ffmpeg -ss 64 -t 36 -i original.mp4 ...
  -filter_complex "
    [0:v]split=5[orig1][orig2]...;
    [orig1]trim=0:4,setpts=PTS-STARTPTS[o1];
    [orig2]trim=4:11,setpts=PTS-STARTPTS[o2];
    ..."

# GOOD: absolute timestamps from full file
ffmpeg -i original.mp4 -i scene1.mp4 -i scene2.mp4 ...
  -filter_complex "
    [0:v]trim=64:68,setpts=PTS-STARTPTS[o1];
    [1:v]scale=1280:720,trim=4:6,setpts=PTS-STARTPTS[s1];
    [0:v]trim=70:75,setpts=PTS-STARTPTS[o2];
    ...
    [o1][s1][o2]...concat=n=N:v=1:a=0[outv];
    [0:a]atrim=64:100,asetpts=PTS-STARTPTS[outa]
  "
  -map "[outv]" -map "[outa]"

ffmpeg -y \
  -i original.mp4 \
  -i generated-scene.mp4 \
  -filter_complex "
    [0:v]trim=START1:END1,setpts=PTS-STARTPTS[o1];
    [1:v]scale=1280:720,trim=0:DURATION,setpts=PTS-STARTPTS[s1];
    [0:v]trim=START2:END2,setpts=PTS-STARTPTS[o2];
    [o1][s1][o2]concat=n=3:v=1:a=0[outv];
    [0:a]atrim=AUDIO_START:AUDIO_END,asetpts=PTS-STARTPTS[outa]
  " \
  -map "[outv]" -map "[outa]" \
  -c:v libx264 -preset fast -crf 18 \
  -c:a aac -b:a 192k \
  output.mp4

© vargHQ, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .claude/skills/ffmpeg-mixing of vargHQ/sdk.

Open the folder on GitHubat commit da4face