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Who published Ffmpeg Mixing?

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

Ffmpeg Mixing by varghq — Agent Skill

Name: Ffmpeg Mixing
Author: varghq

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.

varghq 6971d3d 2.5 KB 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

---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.license: MIT---# 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`

Frequently asked questions