Convert AVI to MKV Online
We first try to move your AVI's existing video and audio streams straight into a Matroska container, which leaves the picture untouched. MKV supports extra audio tracks and subtitles, but this conversion carries over only one video and one audio stream, so it cannot add tracks your AVI never had.
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What AVI to MKV actually changes
AVI is a Microsoft container from the early 1990s. Files you still find with that extension usually hold MPEG-4 Part 2 video (the codec DivX and Xvid encoders produced) with MP3 audio, or sometimes H.264. The container is the problem rather than the video: it has no real place for soft subtitle streams, it handles variable frame rate badly, and media servers such as Plex, Jellyfin and Kodi handle Matroska more predictably than AVI, especially for files that carry a subtitle stream. MKV is the open Matroska container, and it accepts almost any modern codec combination.
Our converter runs ffmpeg 5.1.9 on our servers. For an MKV target it first attempts a plain stream copy, so the compressed video and audio are moved into the Matroska file exactly as they are, with no re-encode. If the Matroska muxer refuses them, the job falls back to a full re-encode: libx264 at the veryfast preset and its default quality level, plus AAC audio at roughly 128 kbps stereo. That fallback is a new encode, so it costs one generation of quality.
Resolution, frame rate and duration survive either path, and on the re-encode path an odd width or height is cropped by a single pixel (641x361 becomes 640x360). What does not survive is anything beyond the one video and one audio stream ffmpeg selects, so a dual-language AVI comes out with a single soundtrack. Chapters are not created, and the rotation flag is not carried over on the copy path, which is worth knowing if the clip came from a phone. Subtitles burned into the picture stay burned in, because they are part of the image.
How to convert AVI to MKV here
- Check the AVI's codec first if you care which path runs: VLC's Tools then Codec Information, or MediaInfo, tells you whether it is MPEG-4 Part 2, H.264 or something older.
- Make sure the file is complete. Part downloads named something like movie_part1.avi, or a capture that was cut off, fail with "Invalid data found when processing input". Join or re-download first.
- Drop the AVI onto this page. A guest can send files up to 50 MB each, a free account 100 MB, Plus 200 MB and Pro 1 GB, with up to 10 files in one request on the guest and free tiers.
- Start the conversion. The file uploads to our servers and a worker runs ffmpeg: stream copy first, automatic H.264 plus AAC re-encode if the copy is rejected.
- Keep the tab open while it works. The page stops waiting after about 10 minutes for files up to 50 MB; if you are signed in you can ask for an email with the link instead, which is useful for a long re-encode.
- Download the .mkv, which keeps the original base name. A size close to the original means the copy path ran.
What this converter does
- Tries a direct stream copy into Matroska, so when the codecs fit the video and audio data is not re-encoded at all
- Falls back automatically to H.264 plus AAC when the stored streams cannot be muxed as they are, instead of failing the job
- Keeps resolution, frame rate and duration; on the re-encode path only an odd pixel row or column is cropped
- Carries one subtitle stream if your AVI genuinely has one, converting it to ASS when the file has to be re-encoded
- Up to 10 files per request on the guest and free tiers, 25 on Plus and 50 on Pro; one request counts as a single job against the hourly limit
- Files over 1 GB are not simply rejected: signed-in users are offered a one-off paid large-file conversion with the result emailed as a link
Video Tutorial
Watch this step-by-step tutorial to learn how to convert AVI files to MKV format online for free using MiConvert.com. No software installation required.
AVI to MKV questions
Can I convert AVI to MKV without losing quality?
When the stream copy succeeds, yes: the compressed video and audio are rewritten into the Matroska container unchanged, so every pixel and sample matches the source. If the copy is rejected, the job re-encodes to H.264 and AAC, which costs one generation of quality. There is no setting to force either path; compare the output size and picture with the original to see which one ran.
Will my MKV keep multiple audio tracks, subtitles and chapters?
No. Matroska as a format supports all three, but this conversion keeps only one video and one audio stream - ffmpeg's default pick, normally the track the file flags as default - so a dual-language AVI loses its second soundtrack. No chapter markers are generated, and we cannot add subtitles that are not already inside the file. If your AVI does carry a soft subtitle stream, one can come through. To keep several tracks, remux locally with MKVToolNix.
Why can't I just rename the file to .mkv?
Because the container is not the extension: AVI and Matroska store their index, timestamps and stream headers in completely different structures, so a renamed file is either rejected or plays with broken seeking. The conversion rebuilds the container properly.
Do you use ffmpeg, and can I set the CRF, preset or resolution?
Yes, ffmpeg 5.1.9 runs server-side, but the arguments are fixed: no CRF, bitrate, resolution, frame rate or trim controls, and no way to convert only part of the video. If you need those, run ffmpeg yourself or use HandBrake; for container work without re-encoding, MKVToolNix is the usual tool.
What are the size and usage limits?
50 MB per file without an account, 100 MB with a free account, 200 MB on Plus and 1 GB on Pro. Guests and free accounts can run 10 conversion jobs per hour per IP address with 2 running at once; Plus and Pro get 50 per hour and 5 at once. One batch request counts as one job, and there is no unlimited tier.
My conversion failed. What do the errors mean?
"Invalid data found when processing input" almost always means the AVI is truncated or is one part of a split file, so re-download or join the parts. A message about an unsupported, proprietary or encrypted codec means our ffmpeg build has no decoder for that stream; re-export the video to H.264 MP4 first. "Processing timed out after 30 minutes" points to a very long or very large source, which you should trim or shrink before retrying.
Will the MKV play on my TV or media player?
VLC, mpv, Plex, Jellyfin and Kodi all read MKV, and many smart TVs do too, but your device still has to decode whatever codec the copy path carried over, such as MPEG-4 Part 2 video. If it refuses the file, use our AVI to MP4 converter instead, since that target always re-encodes to H.264 with AAC.
What happens to my file after the conversion?
Everything runs on our servers, not in your browser. Your uploaded AVI is deleted once the job finishes its final attempt, and the finished MKV stays available through an unguessable download link for about 4 hours before it is deleted automatically. Transfers use HTTPS. We do log file names, sizes, formats and outcomes for operations, and signed-in accounts keep a conversion history entry until the account is deleted.