Can I merge videos with different codecs?

Yes — but you need to re-encode them first. Use the same encoder (libx264) and similar settings for all clips, then use the concat filter method.

What's the fastest way to merge large video files?

If all videos use the same codec (e.g. H.264), use stream copy: ffmpeg -f concat -safe 0 -i concat.txt -c copy merged.mp4 — this takes seconds regardless of file size.

Step-by-Step Guide

How to Merge or Concatenate Videos Together Using FFmpeg

Join multiple video clips into a single file — from two clips to 100+. Methods for fast stream copy (identical codecs) and re-encode (different codecs). Copy-ready commands included.

Method 1: Stream Copy (Fastest — Same Codec)

Create a file called concat.txt:

file 'clip1.mp4'
file 'clip2.mp4'
file 'clip3.mp4'

ffmpeg -f concat -safe 0 -i concat.txt -c copy merged.mp4

This is instantaneous — no re-encoding, zero quality loss.

Method 2: Re-encode (Different Codecs)

ffmpeg -f concat -safe 0 -i concat.txt \
  -c:v libx264 -crf 18 -preset medium \
  merged-quality.mp4

Use this when your clips have different codecs or resolutions.