Video Editor (ffmpeg)

Video editing operations for cutting, merging, converting, and processing video files.

Prerequisites

Requires ffmpeg and ffprobe installed:

brew install ffmpeg

Quick Start

Cut/Trim Video

Extract a segment from a video:

{baseDir}/scripts/cut.sh /path/to/input.mp4 --start 00:00:10 --end 00:00:30 --out /path/to/output.mp4

Or use duration instead of end time:

{baseDir}/scripts/cut.sh /path/to/input.mp4 --start 00:01:00 --duration 30 --out /path/to/output.mp4

Merge Videos

Concatenate multiple videos (must have same codec/resolution):

{baseDir}/scripts/merge.sh video1.mp4 video2.mp4 video3.mp4 --out merged.mp4

Convert Format

Convert between video formats:

{baseDir}/scripts/convert.sh input.mov --format mp4 --out output.mp4

Extract Audio

Extract audio track from video:

{baseDir}/scripts/extract-audio.sh input.mp4 --out audio.mp3

Add Subtitles

Burn subtitles into video:

{baseDir}/scripts/add-subtitles.sh input.mp4 subtitles.srt --out output.mp4

Resize Video

Change video resolution:

{baseDir}/scripts/resize.sh input.mp4 --width 1920 --height 1080 --out output.mp4

Or scale proportionally:

{baseDir}/scripts/resize.sh input.mp4 --scale 720 --out output.mp4

Adjust Speed

Speed up or slow down video:

{baseDir}/scripts/speed.sh input.mp4 --rate 2.0 --out output.mp4   # 2x faster
{baseDir}/scripts/speed.sh input.mp4 --rate 0.5 --out output.mp4   # 0.5x slower

Crop Video

Crop to specific region:

{baseDir}/scripts/crop.sh input.mp4 --x 100 --y 100 --width 800 --height 600 --out output.mp4

Common Workflows

Social Media Clip

Cut a segment and resize for Instagram/TikTok:

# First cut the segment
{baseDir}/scripts/cut.sh input.mp4 --start 00:00:15 --duration 15 --out clip.mp4

# Then resize to vertical format
{baseDir}/scripts/resize.sh clip.mp4 --width 1080 --height 1920 --out tiktok.mp4

Extract Highlights

Cut multiple segments and merge:

{baseDir}/scripts/cut.sh input.mp4 --start 00:00:10 --duration 5 --out highlight1.mp4
{baseDir}/scripts/cut.sh input.mp4 --start 00:01:30 --duration 5 --out highlight2.mp4
{baseDir}/scripts/merge.sh highlight1.mp4 highlight2.mp4 --out highlights.mp4

Add Background Music

Replace or mix audio:

# Replace audio
ffmpeg -i video.mp4 -i music.mp3 -c:v copy -map 0:v:0 -map 1:a:0 -shortest output.mp4

# Mix audio (video audio at 70%, music at 30%)
ffmpeg -i video.mp4 -i music.mp3 -filter_complex "[0:a]volume=0.7[a0];[1:a]volume=0.3[a1];[a0][a1]amix=inputs=2:duration=first" -c:v copy -shortest output.mp4

Tips

• Quality: Use -crf 18 for high quality, -crf 28 for smaller files (default is 23)
• Presets: Use -preset slow for better compression, -preset fast for quicker encoding
• Hardware acceleration: On Apple Silicon, add -c:v h264_videotoolbox for faster encoding
• Copy mode: Use -c copy to avoid re-encoding (much faster, but limited editing)

Troubleshooting

Merge fails with "Codec mismatch"

Videos must have the same codec, resolution, and frame rate. Re-encode them first:

ffmpeg -i input1.mp4 -c:v libx264 -c:a aac -vf "scale=1920:1080" -r 30 temp1.mp4
ffmpeg -i input2.mp4 -c:v libx264 -c:a aac -vf "scale=1920:1080" -r 30 temp2.mp4
{baseDir}/scripts/merge.sh temp1.mp4 temp2.mp4 --out merged.mp4

Subtitles not showing

Ensure subtitle file format matches extension (.srt, .ass, .vtt). Check encoding:

file -I subtitles.srt  # Should show charset=utf-8

Convert if needed:

iconv -f GBK -t UTF-8 subtitles.srt > subtitles_utf8.srt