How do I install the Ffmpeg Mixing skill?

Run npx skillmds@latest add tomevault-io/ffmpeg-mixing in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

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Is Ffmpeg Mixing free to use?

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Who published Ffmpeg Mixing?

tomevault-io (@tomevault-io) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Ffmpeg Mixing by tomevault-io — Agent Skill

Name: Ffmpeg Mixing
Author: tomevault-io

Ffmpeg Mixing

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. Use when this capability is needed.

tomevault-io Updated Sep 17, 2026

File contents

ffmpeg video mixing

Lessons for mixing video clips with ffmpeg while keeping audio and video in sync.

problem: audio/video desync when mixing clips

what went wrong

using -ss X -t Y to pre-trim input, then applying relative trim filters caused timing drift:

# 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];
    ..."

this produced wrong duration (38s instead of 36s) with audio desync.

solution: use absolute timestamps from full input

trim directly from full original using absolute timestamps:

# 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]"

key points

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

example: inserting clips into original

to insert generated clips at specific timestamps while keeping continuous audio:

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

timestamps must add up: (END1-START1) + DURATION + (END2-START2) = AUDIO_END - AUDIO_START

Source: vargHQ/sdk — distributed by TomeVault.

---name: ffmpeg-mixingdescription: 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. Use when this capability is needed.---# ffmpeg video mixingLessons for mixing video clips with ffmpeg while keeping audio and video in sync.## problem: audio/video desync when mixing clips### what went wrongusing `-ss X -t Y` to pre-trim input, then applying relative trim filters caused timing drift:```bash# BAD: relative timestamps after pre-trimffmpeg -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]; ..."```this produced wrong duration (38s instead of 36s) with audio desync.### solution: use absolute timestamps from full inputtrim directly from full original using absolute timestamps:```bash# GOOD: absolute timestamps from full fileffmpeg -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]"```### key points1. **absolute timestamps**: trim from full input file, not pre-trimmed2. **separate audio handling**: use `atrim` on audio stream independently3. **setpts reset**: always use `setpts=PTS-STARTPTS` after trim to reset timestamps4. **scale before trim**: when mixing different resolutions, scale first then trim5. **video duration = audio duration**: ensure total video segments match audio segment length### example: inserting clips into originalto insert generated clips at specific timestamps while keeping continuous audio:```bashffmpeg -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```timestamps must add up: `(END1-START1) + DURATION + (END2-START2) = AUDIO_END - AUDIO_START`---> Source: [vargHQ/sdk](https://github.com/vargHQ/sdk) — distributed by [TomeVault](https://tomevault.io).

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