How to Merge / Join Videos in Avidemux Without Re-encoding
Merging videos in Avidemux means joining multiple clips end-to-end into a single file. It is done with File > Append: you open the first clip, then append the second, third, and so on. As long as every clip shares the same technical parameters, the joined file can be saved in Copy mode — no re-encoding, no quality loss, and it takes seconds.
Step-by-step: join clips in Avidemux
- Open the first clip: File > Open, and select the first video.
- Append the second clip: File > Append, and select the second video. It is added to the end of the timeline.
- Repeat File > Append for every further clip, in the order you want them in the final file.
- Set both outputs to Copy: Video Output >
Copy, Audio Output >Copy. Keep Output Format matching the container you are working with (usuallyMP4 MuxerorMKV Muxer). - Save: File > Save, name the file with the right extension (
.mp4or.mkv), and Avidemux concatenates the clips almost instantly.
The 5-parameter compatibility checklist (why append fails)
Nearly every “append won’t work” problem comes down to this: the clips must have identical encoding parameters. Avidemux does not silently convert mismatched clips — it refuses, produces a broken file, or crashes. Before appending, check these five parameters for every clip (read them under File > Properties):
| # | Parameter | Why it must match |
|---|---|---|
| 1 | Resolution (e.g. 1920×1080) | A decoder cannot switch frame sizes mid-stream; mismatched sizes break the join. |
| 2 | Frame rate (e.g. 30 fps vs 29.97 fps) | Different frame rates desynchronize the timeline — even “almost equal” values fail. |
| 3 | Video codec (e.g. H.264 vs MPEG-4) | Different codecs cannot share one continuous stream. |
| 4 | Audio codec (e.g. AAC vs MP3) | The audio track of the joined file must be one codec throughout. |
| 5 | Audio sample rate (e.g. 48000 Hz vs 44100 Hz) | The most overlooked culprit — check the exact Hz value, not just “AAC”. |
When clips don’t match: normalize, then append
If one or more parameters differ, re-encode each clip to a common target before joining:
- Pick target parameters (for example 1920×1080, 30 fps, H.264 video, AAC audio at 48000 Hz).
- Open each clip in Avidemux, set Video Output to
Mpeg4 AVC (x264)and Audio Output toAAC (Faac), save it as a new file. - If frame rates differ, apply Video > Filters > Resample FPS to the odd ones so they all share the target frame rate.
- Append the normalized clips and save in Copy mode.
This adds one re-encode pass, but it is the only reliable way to join mismatched sources.
Frequently asked questions
Avidemux says “cannot append” — what’s wrong?
Almost always a parameter mismatch. Work through the 5-parameter checklist above (resolution, frame rate, video codec, audio codec, audio sample rate) via File > Properties on each clip. The audio sample rate (e.g. 44100 vs 48000 Hz) is the one people miss most often.
Will joining in Copy mode reduce video quality?
No. In Copy mode Avidemux copies the encoded streams byte-for-byte without decoding them, so there is zero quality loss and the save finishes in seconds. Quality is only affected if you had to re-encode clips to normalize their parameters first.
Can I merge videos with different resolutions?
Not directly — Avidemux will not join clips whose resolutions differ. You must first re-encode them to a common resolution (for example downscale or upscale every clip to 1920×1080 using Video > Filters > Transform > Resize), then append the normalized files.
How many clips can I join at once?
There is no hard limit in Avidemux — File > Append can be repeated as many times as you like, and long joins (dozens of segments) work fine as long as every clip passes the compatibility checklist. Very long timelines may take longer to index when opened, but the save itself stays fast in Copy mode.