How to Use Avidemux for Fast, Free Video TrimmingAvidemux is a lightweight, open-source video editor designed for simple tasks: cutting, filtering, and encoding. It’s ideal when you need to trim a video quickly without re-encoding or pay for complex software. This guide walks you step-by-step through installing Avidemux, loading video files, trimming efficiently, exporting with or without re-encoding, and troubleshooting common issues.
Why choose Avidemux?
- Free and open-source — no cost, no trial limits.
- Fast trimming without re-encoding — if you keep the same codecs, edits can be lossless and almost instant.
- Cross-platform: Windows, macOS, Linux.
Download and install
- Go to the official Avidemux website and download the version matching your OS.
- Install following the platform-specific instructions (Windows: run installer; macOS: mount DMG and copy app; Linux: use package manager or AppImage).
- Launch Avidemux.
Basic interface overview
- Project timeline / seek bar: where you navigate through the video.
- A and B markers: set start (A) and end (B) points for trims.
- Video, Audio, and Output format panes: configure codecs and container formats.
- Filters: resize, crop, deinterlace, sharpen, subtitle, etc.
- Preview pane: shows the current frame.
Preparing your project
- File → Open → choose your video (Avidemux supports many formats: MP4, MKV, AVI, MPEG, more).
- Check the video properties at the bottom of the window to confirm codec/container.
Tip: If you want truly lossless trimming, ensure the Video output and Audio output are set to “Copy” and choose a compatible Output format/container (e.g., MP4 for H.264 video).
Fast, lossless trimming (no re-encoding)
This method keeps the original video and audio streams untouched; processing is very fast and preserves quality.
- Set Video output to Copy.
- Set Audio output to Copy.
- Choose an Output format compatible with the original streams (commonly MP4, MKV, or AVI).
- Use the seek bar to find the exact frame where you want the trimmed video to begin.
- Use the frame-step buttons (or arrow keys) for precise navigation.
- Click the “A” button to set the start marker.
- Move to the end point and click “B” to set the end marker.
- Optional: Press Play to preview the selected segment.
- File → Save → give a filename with the correct extension (e.g., .mp4).
- Avidemux will save only the segment between A and B without re-encoding — very fast.
Important: Container and codec compatibility matters — some containers require re-muxing or will not accept certain codec copies. If saving fails, switch the Output format (e.g., try MKV).
Trimming with re-encoding (when you need format change or filters)
If you need to apply filters (crop, resize, color correction), or convert codecs, you must re-encode.
- Set Video output to a codec (e.g., x264 for H.264).
- Click Filters to add and configure filters (crop, resize, denoise, subtitles). Apply and close.
- Set Audio output to a codec if audio re-encoding is needed (e.g., MP3, AAC).
- Choose an appropriate Output format.
- Set A and B markers as above.
- File → Save → give a filename. Encoding will take longer depending on length and settings.
Quick encoding tips:
- Use x264 with preset options if available for faster encoding.
- Lower resolution or bitrate to reduce file size and speed up encoding.
- On slow machines, limit filter use and choose faster encoder settings.
Cutting multiple segments and joining
Avidemux can save only one continuous segment at a time. To extract multiple parts and join them:
Method A — Manual concatenation (preserves copy mode if streams match):
- Extract each segment individually using Copy for audio/video and the same container.
- Use a separate tool (e.g., mkvmerge for MKV) to concatenate files, or use Avidemux to append segments by opening the first file, then File → Append → add next segment (works if codecs/containers are identical).
Method B — Re-encode multiple cuts into one file:
- Open the first segment, set Video/Audio output to an encoding codec, and append other segments (File → Append).
- Save the combined file; Avidemux will re-encode the appended project.
Useful filters for trimming workflows
- Crop: remove unwanted edges or black bars.
- Resize: downscale for smaller files or upsize for compatibility (not recommended for quality).
- Deinterlace: fix interlaced footage.
- Subtitles: add or burn-in subtitle files.
- Time shift: adjust audio sync.
Filters are applied in the Filters dialog; preview changes before encoding.
Common problems and fixes
- Save fails or file won’t play: try a different Output format (MKV is forgiving).
- A/B markers snap to keyframes: Copy mode requires cuts at keyframes; use re-encoding for frame-accurate cuts.
- Audio/video out of sync after edits: try re-encoding audio or use the Time shift filter.
- Crashes on certain formats: convert source to a standard container (e.g., remux MP4 to MKV) and retry.
Example—Fast trim from 00:01:20 to 00:02:45 (lossless)
- Open video.
- Set Video/Audio output = Copy; Output format = MP4 or MKV.
- Seek to 00:01:20, set A. Seek to 00:02:45, set B.
- File → Save → filename.mp4. Result saved quickly without quality loss.
Performance tips
- For faster encoding, enable hardware acceleration if your build supports it (e.g., VAAPI, NVENC) — check Avidemux build options.
- Close other intensive apps while encoding.
- For batch trims, create a simple script using command-line tools like FFmpeg if Avidemux becomes slow for many files.
Alternatives and when to switch
Avidemux is great for quick trims and simple edits. If you need multi-track timelines, advanced effects, or professional color grading, consider switching to editors like DaVinci Resolve, Shotcut, or Kdenlive.
Summary
Avidemux offers a fast, no-cost way to trim videos with minimal fuss. Use Copy mode for instant, lossless cuts when possible; switch to re-encoding when you need filters or frame-accurate edits. With a few clicks you can extract, join, and export segments efficiently.
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