Convert MKV to MP4
MKV is Matroska - a container built for lossless preservation and lots of tracks. When the video and audio are already MP4-compatible (H.264, HEVC, AAC, MP3), Wave just repackages the streams. No re-encode, no quality loss, no upload.
What actually changes
Most MKVs store H.264 or HEVC video with AAC or AC-3 audio - codecs MP4 accepts as-is. So a proper MKV-to-MP4 conversion isn't a re-encode at all; it's a re-mux. Wave inspects the streams first, and if they fit, it rewrites the container header and moves the moov atom to the start of the file for fast-start playback. The pixels and audio samples are untouched.
Where remux won't work: MKV files that carry codecs MP4 can't hold (VP9, Vorbis, some FLAC), or files with more than one video track. Wave detects those and re-encodes only what it has to, using LGPL codecs - never GPL x264 - so no licensing surprises land in the output.
Three steps.
-
01
Step 1
Drop your MKV file onto the card, or click "Pick a video".
-
02
Step 2
Wave inspects the source and shows whether it can fast-copy or needs to re-encode.
-
03
Step 3
Hit convert. Save the MP4 when it finishes.
Answers, specifically.
Will converting MKV to MP4 reduce quality?
Not if the video and audio codecs are MP4-compatible (H.264, HEVC, AAC, MP3). Wave copies the streams as-is. It only re-encodes when the source uses codecs MP4 physically cannot hold - VP9 and Vorbis are the usual culprits.
Can iOS or QuickTime play MKV?
No. That's the main reason this conversion exists. MP4 with H.264 or HEVC plays natively on iOS, macOS, Windows, Android, and every browser.
Does my MKV get uploaded anywhere?
No. Wave loads FFmpeg into your browser as WebAssembly and runs the conversion locally. The bytes never leave the tab. You can open your browser's network panel while converting and see for yourself.
How large a file can I convert?
About 1.5 GB comfortably on a desktop browser. The real cap is your browser's RAM - very large files may fail on machines with less memory. Wave warns above 500 MB and refuses above 1.5 GB.
Why is the MP4 sometimes slightly larger than the MKV?
MKV can pack its index a little tighter. A remuxed MP4 usually gains a few percent from container overhead and the fast-start rewrite that puts the moov atom at the front of the file.