Avidemux Copy Mode vs Re-encoding: What “Copy” Actually Means
Copy mode in Avidemux means the video (or audio) stream is copied bit-for-bit from the input file to the output file without being decoded or re-encoded. Nothing about the picture or sound data changes: no quality is lost, and the job finishes in seconds rather than minutes. The trade-off: because the compressed data is passed through untouched, you can only cut on keyframes, you cannot use any filters, and the output container must accept the source codecs as-is.
Re-encoding is the opposite: Avidemux decodes every frame to raw pixels, applies your edits and filters, then compresses everything again with the encoder you chose (e.g. x264). It is slower and loses a little quality, but it allows frame-accurate cuts, filters, and any valid codec/container combination.
This distinction — Copy vs re-encode — is the single most important concept in Avidemux. Nearly every confusing behavior beginners hit (greyed-out filters, save errors, “too short” warnings) traces back to it.
Copy vs re-encode at a glance
| Copy mode | Re-encoding | |
|---|---|---|
| What happens | Stream copied untouched | Decoded, processed, compressed again |
| Speed | Seconds (disk speed) | Minutes (CPU/GPU speed) |
| Quality | Lossless — bit-identical | Small generation loss (tunable) |
| Cut precision | Keyframes only | Any frame |
| Filters | Not available (disabled) | Fully available |
| Container freedom | Container must accept source codecs | Any valid combination |
Decision guide: which tasks allow Copy?
| Task | Mode | Notes |
|---|---|---|
| Cut / trim a video | Copy | Cut on keyframes; see lossless cutting |
| Split into parts | Copy | Keyframe rules apply; see splitting guide |
| Join / append clips | Copy | Clips must match parameters; see merging guide |
| Remove an audio track | Copy (video) | See remove audio |
| Extract audio to MP3 | N/A (audio only) | See extract audio |
| Rotate / resize / filters / subtitles burn-in | Re-encode | Pixel changes require an encoder |
| Change volume / normalize audio | Re-encode audio (video can stay Copy) | See volume guide |
| Compress / shrink file size | Re-encode | See compress video |
| Convert container (e.g. MKV → MP4), same codecs | Copy | Remuxing; container must support the codecs |
The hybrid: Copy video + re-encode audio
The two dropdowns — Video Output and Audio Output — are independent. The most useful hybrid: Video Output = Copy with Audio Output = an encoder (AAC/MP3). You get lossless, instant video plus processed audio — exactly what the volume/normalize workflow and the audio-shift sync fix use. This combination is why Avidemux exposes the two settings separately.
Why so many errors trace back to this setting
- Filters greyed out? Video Output is on Copy — filters need an encoder. (Fix)
- “Muxer: Cannot open”? Copy mode asked the container to accept codecs it cannot hold. (Fix)
- “Too short” after saving? Copy-mode cuts on non-keyframes broke the timestamps. (Fix)
- Append failing? Copy mode demands matching parameters across clips. (Fix)
When something in Avidemux behaves unexpectedly, check the Video/Audio Output dropdowns first — nine times out of ten, the answer is there.
Frequently asked questions
What is Copy mode in Avidemux?
Copy mode copies the video or audio stream bit-for-bit from input to output without decoding or re-encoding it. It is lossless and very fast, but limited to keyframe cuts, no filters, and containers that accept the source codecs.
Does Copy mode lose quality?
No — the compressed data is passed through untouched, so the output is bit-identical to the input for that stream. Quality loss only occurs when re-encoding.
Why are my filters greyed out?
Because Video Output (or Audio Output, for audio filters) is set to Copy. Filters modify the data, which requires decoding and re-encoding — select a real encoder to unlock them.
Can I use Copy for video but re-encode the audio?
Yes — the Video Output and Audio Output settings are independent. Video = Copy plus Audio = AAC/MP3 is a common and fully supported combination.