Top 8 AVI to MKV Converters in 2026 (Tested for Windows, Mac & Online)

Editor's Pick — Top 3 AVI to MKV Converters in 2026

Best Overall: UniFab Video Converter — 9.5/10 Free with no watermark, drag-and-drop GUI, stream-copy lossless mode for instant rewrap, batch processing, 1000+ format support. Native Windows and Mac builds.

Best Open-Source: HandBrake — 8.8/10 Free forever, cross-platform including Linux, deep parameter control. The right pick for power users.

Best Online (No Install): CloudConvert — 7.6/10 Browser-based, handles common conversions for files under ~1 GB. Trade-off is uploading to a third-party cloud.

The rest of this guide covers all 8 tools, scoring methodology, and the "remux vs re-encode" decision that affects every AVI-to-MKV conversion.

AVI vs MKV: Why Convert AVI to MKV?

AVI (Audio Video Interleave) is a Microsoft container from 1992 — still in use but technologically limited. MKV (Matroska) is the modern open-source container that solves most of AVI's problems:

• Multiple subtitle tracks — MKV supports many subtitle streams; AVI is limited
• Multiple audio tracks — MKV holds multiple language tracks cleanly; AVI struggles with more than one
• Modern codec support — MKV holds H.265, AV1, VP9, Opus, and other modern codecs; AVI's codec list is older
• Chapter support — MKV has proper chapter metadata; AVI doesn't
• Streaming compatibility — MKV plays in modern hardware players and TVs; AVI is hit-or-miss
• Smaller files — MKV's container overhead is more efficient than AVI's

The most common reason to convert is preserving an old AVI archive in a future-proof container without losing the original streams.

Quick Comparison: Top 3 AVI to MKV Converters

Best AVI to MKV Converters for Windows

1. UniFab Video Converter

Platform: Windows, Mac | Price: Free

UniFab Video Converter is our top pick for AVI-to-MKV conversion on Windows. The free tier has no watermark, no time limit, no resolution cap. The format library covers AVI (with all its codec variants — Xvid, DivX, MJPEG) as input, and MKV with any modern video/audio codec as output. Batch processing handles folders, GPU acceleration uses NVIDIA, AMD, or Apple Silicon, and the built-in editor handles basic trim/crop without needing a separate tool.

Stream-copy mode rewraps AVI as MKV in seconds because no re-encoding happens — the right choice when you just want a modern container around existing streams.

How to Convert AVI to MKV with UniFab:

Step 1: Launch UniFab and select the Converter module. Drag and drop your AVI file or click Add to browse.

Step 2: Select MKV as the output format. Customize codec, resolution, and sample rate if needed. Click Start to begin conversion.

Strengths: clean GUI, stream-copy mode, batch processing, GPU acceleration, no watermark 

Weaknesses: Windows + Mac only (no Linux build)

2. AVS Video Converter

Platform: Windows, Mac | Price: $49/year or $79 lifetime

AVS Video Converter is a long-running Windows-only commercial converter with broad format coverage. The free trial adds watermarks; paid pricing is mid-range. UI is functional but dated compared to UniFab.

How to Convert AVI to MKV Using AVS Video Converter

1. Step 1: After opening this program on your Windows, head to the top to select the “To MKV” option > select “Browse” > add your preferred AVI video to the tool.
2. Step 2: Once you see the “Profile” drop-down menu, open it and select your appropriate preset. Then, select the “Convert Now” option to start the AVI to MKV conversion process.

Strengths: broad codec support, decent batch features 

Weaknesses: Windows only, watermarks on free, less GPU acceleration than UniFab

Best AVI to MKV Converters for Mac

3. HandBrake

Platform: Windows, macOS, Linux | Price: Free (open source)

HandBrake is the cross-platform open-source standard and our Mac pick when you want a free tool. Native Apple Silicon build, deep parameter control, free forever. The Mac UI is the same as Windows and Linux — dated but functional.

How to Convert AVI to MKV Using HandBrake

1. Step 1: Once you open this free tool on your Mac, select the “Source” in the upper left side of the screen > Open File.
2. Step 2: Select your required AVI file for conversion > head to the “Destination” > select “Browse” to decide the location to save the converted MKV file.
3. Step 3: Next, select the “Start” option in the main window for completing the conversion process. 

Strengths: open-source, native Apple Silicon, deep control, free forever 

Weaknesses: steeper learning curve than UniFab Video Converter

4. VLC Media Player

Platform: Windows, macOS, Linux | Price: Free (open source)

VLC includes a free converter buried in Media → Convert/Save. It works, it's already installed on most Macs, and it's free. Quality and format options are limited compared to dedicated converters, and the conversion UI is rough.

How to Convert AVI to MKV Using VLC

1. Step 1: Open the VLC program on your Mac. Then, go to the “Media” menu at the upper left side of the program and select “Convert/ Save.”
2. Step 2: Go for the “Add” option in the menu > add your wanted AVI file for conversion.
3. Step 3: Under the “Output” section, select MKV > select “Convert” to start the AVI to MKV conversion process.

Strengths: already installed, cross-platform 

Weaknesses: limited format options, slower than dedicated tools

Best Free Online AVI to MKV Converters

5. CloudConvert

CloudConvert is the most flexible browser-based AVI-to-MKV converter in 2026. Free credits handle several conversions per month; paid plans scale. The catch is privacy: your AVI file is uploaded to CloudConvert's cloud for processing.

How to Convert AVI to MKV: Go to cloudconvert.com, select AVI to MKV, upload your file, adjust settings if needed, and click Convert.

Strengths: generous free quota, broad format support, no install 

Weaknesses: cloud upload required, slower than desktop on large files

6. VEED.io

Platform: Online | Price: Free (limited); Pro from $18/month

VEED.io is a browser-based editor that includes conversion. Free tier watermarks the output; paid tier removes it. Useful if you want conversion + light editing in one place.

How to Convert AVI to MKV Using Veed.io

1. Step 1: You can open this program using any web browser. Upload your required AVI file to the tool using drag & drop option.
2. Step 2: Otherwise, on your device, select the Blue button to select the AVI file from the folder. You can also add the file from the Dropbox, YouTube URL, etc.
3. Step 3: Once you see the list of file types in the drop-down menu, select MKV as the output format. Then, select the “Convert File” option to begin the conversion process.

Strengths: editing features bundled, no install 

Weaknesses: watermarks on free output, slower than dedicated converters

7. FreeConvert

FreeConvert is a simple multi-tool web platform. Handles AVI-to-MKV cleanly with file size limits on the free tier and no watermark on small files.

How to Convert AVI to MKV: Go to freeconvert.com, select AVI to MKV, upload your file or import from cloud storage, adjust settings, and click Convert.

Strengths: clean UI, no watermark on small files 

Weaknesses: tight free-tier file size limits

8. Converter App

Platform: Online | Price: Free

A lighter web converter for one-off small-file conversions. Free, simple, but limited format library compared to CloudConvert.

How to Convert AVI to MKV Using Converter App

1. Step 1: After opening this tool on your device using any browser, upload the AVI you want to convert to MKV format in the left-side upload box.
2. Step 2: The uploaded AVI file will be automatically converted to your selected MKV format within a few seconds.
3. Step 3: After finishing the auto-conversion, you will see a “Download” option, which you need to select for your desired results.

Strengths: simple, free 

Weaknesses: small format library, file size limits

Full Comparison: All 8 AVI to MKV Converters

Remux vs Re-encode — The Choice That Matters Most

This is the single decision that determines speed, file size, and quality for any AVI-to-MKV conversion:

Remux (Stream-copy mode): The converter extracts the existing video and audio streams from AVI and wraps them in MKV without touching them. Finishes in seconds. No quality loss. File size is roughly the same as input.

• When to remux: the AVI's codecs (H.264, MPEG-4, AAC, AC3, MP3) are MKV-compatible AND you just want a modern container. This is the right pick most of the time.

Re-encode: The converter decodes the AVI's video and audio streams, then re-encodes them to a target codec inside MKV. Takes minutes to hours. Quality is good but not lossless. File size depends on target bitrate.

• When to re-encode: the AVI uses legacy codecs (Xvid, DivX, old MPEG-4) that some MKV players don't support, OR you want to convert old footage to modern codecs (H.265, AV1) for smaller file size

UniFab Video Converter's "Lossless" toggle picks the remux path automatically. In FFmpeg, the command is ffmpeg -i input.avi -c copy output.mkv. Most other tools have a similar option somewhere in advanced settings.

Tips for Best AVI to MKV Conversion Results

1. Try remux first — instant and lossless when codecs allow
2. For re-encode, use H.264 + AAC as output codecs for universal compatibility
3. Or use H.265 + Opus for smaller files when you control playback devices
4. Batch large folders with UniFab Video Converter or HandBrake Queue
5. For full FFmpeg syntax, see our FFmpeg WebM to MP4 guide — the same flags apply to AVI input
6. Verify the output plays on your target device before deleting the source AVI

Conclusion

Converting AVI to MKV in 2026 is essentially a container swap — the streams inside don't need to change for most use cases. UniFab Video Converter is our editor's pick for the cleanest free desktop workflow with stream-copy lossless mode. HandBrake is the open-source alternative. CloudConvert handles the no-install browser path. Pick remux mode when codecs allow; pick re-encode when you need to modernize the codecs themselves.

FAQs about AVI to MKV

What is the best free AVI to MKV converter in 2026?

UniFab Video Converter is our editor's pick. Free tier has no watermark, no time limit, no resolution cap, supports stream-copy mode for instant lossless conversion, and runs batch jobs on folders. Native Windows and Mac builds with GPU acceleration. HandBrake is the strong open-source alternative if you want a free-forever cross-platform tool.

Can I convert AVI to MKV without losing quality?

Yes via remux (stream-copy) mode. The converter rewraps the existing video and audio streams in MKV without touching them — no decoding, no encoding, no quality loss. UniFab Video Converter's "Lossless" toggle does this automatically. FFmpeg's -c copy flag is the same operation. Re-encoding is also possible if you specifically want to modernize codecs, but it goes through a quality-loss step.

What is the difference between remux and re-encode?

Remux extracts the existing streams and rewraps them in a new container — fast, lossless, file size similar to input. Re-encode decodes the streams and converts them to different codecs — slower, quality depends on settings, file size depends on bitrate. For AVI-to-MKV, remux is the right pick most of the time because both containers can hold the same codec streams.

How long does AVI to MKV conversion take?

Remux mode finishes in seconds for any file size because no decoding/encoding happens. Re-encoding takes longer — a 2-hour 1080p AVI converts in 5-15 minutes on modern desktop with GPU acceleration. Online converters add upload + download time, often making them slower than desktop for large files.

Can I batch convert multiple AVI files to MKV at once?

Yes. UniFab Video Converter lets you drop multiple AVI files into the workspace and convert all at once. HandBrake has a Queue feature. FFmpeg uses shell loops: for f in *.avi; do ffmpeg -i "$f" -c copy "${f%.avi}.mkv"; done. For 100+ files, the FFmpeg approach is fastest because it runs headless.

Does converting AVI to MKV reduce file size?

Remux mode keeps file size roughly the same as input — only the container metadata changes, not the streams themselves. Re-encoding to modern codecs (H.265, AV1) can dramatically reduce file size, often 30-50% smaller than the original AVI at equivalent visual quality. The trade-off is compatibility narrows because not every player supports H.265 or AV1.

Can VLC convert AVI to MKV?

Yes. Open VLC, click Media → Convert/Save, add your AVI file, choose MKV as the output, pick a destination, hit Start. VLC is free, cross-platform, and probably already installed. The trade-off vs dedicated converters is fewer format options, no batch features, and a rougher UI. For occasional one-off conversion, VLC is fine.

Is it safe to use online AVI to MKV converters?

Generally yes for non-sensitive content. CloudConvert, FreeConvert, and VEED.io publish data retention policies and delete files after processing. The risk is your file uploads to a third-party server and stores at least temporarily. For sensitive footage — family video, work projects, anything personal — use a desktop converter like UniFab Video Converter or HandBrake that keeps the file local.

Is MKV better than AVI for modern playback?

Yes for almost every modern use case. MKV supports modern codecs (H.265, AV1, VP9, Opus), multiple subtitle and audio tracks, chapter metadata, and plays on more modern hardware players and TVs than AVI. AVI is still around for legacy archives and very old footage; if you're converting old AVI files for modern playback, MKV is the right target container.

Does converting AVI to MKV require special hardware?

No for remux mode — it runs on any computer in seconds because no encoding happens. For re-encoding to modern codecs, a discrete GPU (NVIDIA RTX 3060+, AMD RX 6000+, or Apple Silicon M2+) makes encoding meaningfully faster. CPU-only encoding still works but takes 2-4× longer. UniFab Video Converter and HandBrake both use hardware encoders when available (NVENC, QuickSync, VideoToolbox).