The fastest way depends on what you already have installed

Merging two video files means combining them into a single output video, one after the other. The method you choose depends on whether you want a simple tool that does only this, or software you might use for other editing tasks. Most computers come with something that can do it — Windows has Photos, macOS has iMovie — but dedicated tools like FFmpeg (command line), DaVinci Resolve (free version), or Shotcut give you more control over quality and format.

The trade-off is speed versus flexibility. Built-in tools are faster to open and understand but offer fewer options. Command-line tools like FFmpeg are fastest for repeated merges but require typing commands. Video editors like DaVinci Resolve or Shotcut let you trim, reorder, or adjust audio between clips, but take longer to load and learn.

Key Takeaways

  • Windows Photos and macOS iMovie can merge videos without installing anything new, though they work best with videos already in common formats like MP4.
  • FFmpeg is the fastest method if you merge videos often, because you type one command and it finishes in seconds, but it requires learning command-line syntax.
  • DaVinci Resolve and Shotcut are free video editors that let you trim, reorder, or adjust audio between clips before merging, and work on Windows, macOS, and Linux.
  • The output file size and quality depend on the codec and bitrate of your source videos — merging does not re-encode unless you change these settings.

Using Windows Photos or macOS iMovie (no installation needed)

Windows Photos is built into Windows 10 and later. Open Photos, click "Create" at the top, then select "Video with music". Drag your first video into the timeline, then drag your second video directly after it. Click "Export" at the top right and choose your quality (1080p, 4K, or original). The export takes a few minutes depending on file size. Photos works best if both videos are already MP4 files; if one is MOV or MKV, it may fail or take much longer.

macOS iMovie works similarly. Open iMovie, create a new project, drag your first video into the timeline, then drag your second video to the right of the first. Click "File" → "Share" → "File" and choose your resolution. iMovie handles most video formats, but very large files (over 4 GB) sometimes cause crashes.

Both tools are convenient because they are already on your computer, but they do not show you the exact bitrate or codec of the output, and they re-encode the video (which takes time and may reduce quality slightly). If your videos are already high quality and you want to keep them that way, a command-line tool is faster.

Using FFmpeg from the command line (fastest for repeated merges)

FFmpeg is a free command-line tool that merges videos without re-encoding them, so the output is identical in quality to the source. Download it from ffmpeg.org, install it, then open your terminal (Command Prompt on Windows, Terminal on macOS or Linux).

Create a text file called concat.txt in the same folder as your videos. Inside, type:

file 'video1.mp4' file 'video2.mp4'

Replace video1.mp4 and video2.mp4 with your actual filenames. Save the file, then open your terminal, navigate to that folder, and type:

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

FFmpeg finishes in seconds because it copies the video data without re-encoding. The trade-off is that both videos must have the same resolution, frame rate, and codec — if they do not, FFmpeg will fail with an error message. If that happens, you can re-encode both to match first (slower, but guarantees it works), or use a video editor instead.

Using DaVinci Resolve (free, with editing options)

DaVinci Resolve is a professional video editor with a free version that runs on Windows, macOS, and Linux. Download it from blackmagicdesign.com, install it, and open it.

Create a new project, then drag both videos into the media pool (the left panel). Drag your first video to the timeline at the bottom, then drag your second video to the right of it. If you want to trim either clip, click it on the timeline and drag the edges. If you want to adjust audio levels or add a fade between clips, right-click the clip and choose the option you need.

When you are ready to merge, click "File" → "Export" at the top. Choose "MP4" as the format, set the resolution to match your source videos (usually 1080p or 4K), and click "Export". DaVinci Resolve re-encodes the video, so the export takes longer than FFmpeg, but you have full control over every frame and can make adjustments before merging.

Using Shotcut (simple editor, works on all platforms)

Shotcut is a free, lightweight video editor available for Windows, macOS, and Linux. Download it from shotcut.org and install it.

Open Shotcut, then go to "File" → "Open" and select your first video. Drag it to the timeline at the bottom. Go to "File" → "Open as Layers" and select your second video — it will appear on a second track. Click the second track and drag it to the right so it starts after the first video ends. You can see the exact frame where the first video ends by looking at the timeline ruler.

When both videos are positioned correctly, go to "File" → "Export" and choose "MP4" or your preferred format. Shotcut re-encodes, so the export takes a few minutes. Shotcut is simpler than DaVinci Resolve and faster to learn, but has fewer advanced editing tools.

Comparing file size and quality after merging

The output file size depends on the codec and bitrate of your source videos. If you use FFmpeg with the -c copy flag, the output file size is roughly the sum of the two input files, because no re-encoding happens. If you use Photos, iMovie, DaVinci Resolve, or Shotcut, the output is usually slightly larger because they re-encode.

Quality loss from re-encoding is usually invisible to the human eye, especially if both source videos are already compressed (MP4, H.264). If your source videos are very high bitrate (over 50 Mbps) or in a lossless format, use FFmpeg to avoid any quality loss.

If your two videos have different resolutions (one is 1080p, one is 4K), all four tools will ask you to choose an output resolution. Choosing the lower resolution (1080p) is faster; choosing the higher resolution (4K) requires upscaling the lower-resolution video, which does not improve quality but does increase file size.

What to do if the merge fails

The most common reason a merge fails is that the two videos have different codecs or frame rates. FFmpeg will tell you this in an error message. To fix it, use DaVinci Resolve or Shotcut instead — they can convert both videos to the same format before merging.

If the output file is corrupted or will not play, the merge was interrupted. This usually happens if your hard drive ran out of space during export. Free up at least 10 GB of space and try again. If it happens repeatedly, your hard drive may be failing — try exporting to a different drive if you have one.

If one video is much larger than the other (one is 100 MB, one is 5 GB), the merge will still work, but the output will be the sum of both sizes. There is no way to compress during a merge without re-encoding and losing quality.

Frequently Asked Questions

Can I merge videos that are different formats, like MP4 and MOV?

FFmpeg will fail if the codecs inside the files are different. Photos, iMovie, DaVinci Resolve, and Shotcut can handle different formats because they re-encode everything to one format before merging. If you use FFmpeg, convert both videos to MP4 first using one of the editors, then merge with FFmpeg.

Does merging reduce video quality?

FFmpeg with the -c copy flag does not reduce quality because it copies the video data without re-encoding. Photos, iMovie, DaVinci Resolve, and Shotcut all re-encode, which can reduce quality slightly, but the loss is usually not visible unless your source videos are very high bitrate or shot in a lossless format.

How long does it take to merge two videos?

FFmpeg takes seconds because it does not re-encode. Photos, iMovie, DaVinci Resolve, and Shotcut take minutes to hours depending on the total file size and your computer's speed. A 1 GB video usually takes 5 to 15 minutes to export on a modern computer.

Can I add a transition or fade between the two videos?

FFmpeg cannot add transitions — it only concatenates. DaVinci Resolve and Shotcut both let you add fades, dissolves, or other transitions by right-clicking between the two clips on the timeline. iMovie and Photos have limited transition options in their menus.

What if I want to merge more than two videos?

All four methods work with three or more videos. In FFmpeg, add more lines to your concat.txt file. In the editors, drag each video to the timeline one after the other. The process is the same, just longer.