How to Merge (Concatenate) Videos with FFmpeg: From Lossless to Universal

Do you have a sequence of video clips (clip1.mp4, clip2.mp4, clip3.mp4) that you want to join into a single, seamless video? FFmpeg offers several powerful methods to do this, including an incredibly fast technique that doesn't even require re-encoding.

This guide covers the two most essential methods for merging videos.

🚀 Quick Path: Method 1 (Lossless Concatenation)

When to use it: When all your video clips have the exact same codecs, resolution, and frame rate (e.g., they are sequential clips from the same camera or phone).

This method is lightning-fast because it directly concatenates the data streams without re-encoding, thus preserving the original quality.

Step 1: Create a text file

First, create a text file, for example mylist.txt, with the following content:

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

Step 2: Run the FFmpeg command

Next, run the following command in your terminal:

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

🧠 The Breakdown: What Each Parameter Means

Parameter	Explanation
ffmpeg	Starts the FFmpeg program.
-f concat	-f (format) forces the input format to use the concat demuxer, which is the key to this lossless method.
-safe 0	This is a security option that allows the use of relative or absolute file paths in your list file. It's required for simple filenames.
-i mylist.txt	Specifies the input file containing the list of videos to merge.
-c copy	Short for "codec copy," this tells FFmpeg to copy the video and audio streams directly without re-encoding.
final_video.mp4	The filename for the final, merged output video.

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🧠 Method 2: The Concat Filter (Re-encoding)

When to use it: When your video clips have different formats, resolutions, or frame rates.

This method re-encodes all video streams to make them uniform. It offers maximum compatibility but takes significantly more time.

The FFmpeg Command:

ffmpeg -i clip1.mp4 -i clip2.mov -i clip3.webm -filter_complex "[0:v][1:v][2:v]concat=n=3:v=1:a=1[v][a]" -map "[v]" -map "[a]" final_video.mp4

The Breakdown:

Parameter	Explanation
-i clip1.mp4 ...	List all videos you want to merge as separate input files.
-filter_complex	Used to define a complex filtergraph.
"[0:v][1:v][2:v]..."	[0:v] refers to the video stream of the first input, [1:v] to the second, and so on.
"...concat=n=3:v=1:a=1..."	Calls the concat filter. n=3 specifies there are 3 input segments; v=1 means there will be 1 output video stream; a=1 means 1 output audio stream.
"...[v][a]"	Names the final concatenated video and audio streams as [v] and [a] respectively.
-map "[v]" -map "[a]"	"Maps" the named video and audio streams to the final output file.

Conclusion: If your clips are all in the same format, always prefer Method 1 for its incredible speed and quality preservation. If your clips are mismatched, Method 2 provides the robust compatibility needed to join them all correctly.