How to convert MKV to MP4 on Mac, free and without losing quality

Short answer: install FFmpeg, then run ffmpeg -i input.mkv -map 0 -c copy -c:s mov_text output.mp4. That copies the video, audio and subtitles into an MP4 without re-encoding, so it takes seconds and the quality is identical. If the result has no sound or will not open, the fixes are below.

We ran every command in this guide on a Mac with macOS 26 and FFmpeg 9.0.1, then opened each MP4 with Apple’s own media framework, the one QuickTime uses, to check it really plays.

First: do you need to convert at all?

MKV is a container, a box that holds video, audio and subtitle tracks. QuickTime refuses the box even when the video inside is ordinary H.264. If all you want is to watch the film, a player that opens MKV directly is quicker than any conversion and keeps every audio language and subtitle track. Stoic, IINA and VLC all do. See how to play MKV files on Mac and the best video players for Mac.

Convert when something else needs an MP4: iMovie or Final Cut, an iPhone or iPad, a TV that only reads MP4, or someone you are sending the file to.

Which method should you use?

Method 1: convert MKV to MP4 in Terminal with FFmpeg (free, lossless)

FFmpeg is the free, open-source tool most video apps are built on. The easiest way to install it is Homebrew. Open Terminal and run:

brew install ffmpeg

Then go to the folder with your film (type cd , drag the folder onto the Terminal window and press Return) and use the command that matches your file.

H.264 video (most MKV files)

ffmpeg -i input.mkv -map 0 -c copy -c:s mov_text output.mp4

-map 0 keeps every track, -c copy copies the video and audio untouched, and -c:s mov_text turns text subtitles into the format MP4 uses. In our test, the same command without that last part failed, because MP4 cannot hold SRT subtitles as they are. A 115 MB file took 0.12 seconds.

HEVC (H.265) video, common in 4K files

ffmpeg -i input.mkv -map 0 -c copy -c:s mov_text -tag:v hvc1 output.mp4

The -tag:v hvc1 part matters. Without it our HEVC MP4 was a valid file that QuickTime still refused to open; with it, it played.

MP4 plays but there is no sound (DTS or TrueHD audio)

ffmpeg -i input.mkv -map 0 -c copy -c:a aac -b:a 320k -c:s mov_text output.mp4

Films often carry DTS or TrueHD audio. Copied into an MP4, our DTS test file opened in QuickTime with the sound track missing. This command still copies the video untouched but converts the audio to AAC, which plays everywhere. Only the audio is re-encoded, and AAC at 320 kbps is hard to tell from the original on most speakers.

Convert a whole folder at once

for f in *.mkv; do ffmpeg -i "$f" -map 0 -c copy -c:s mov_text "${f%.mkv}.mp4"; done

This converts every MKV in the folder and keeps the names, including names with spaces. Add -tag:v hvc1 before the output name if the files are HEVC.

What a remux cannot do

• Image-based subtitles from Blu-ray rips (PGS) cannot become MP4 text subtitles without text recognition. Leave them out with -map 0:v -map 0:a instead of -map 0.
• Older codecs that MP4 does not support need a real conversion, so use HandBrake.
• Dolby Vision files are better played directly than converted. See how to play Dolby Vision MKV on Mac.

Method 2: convert MKV to MP4 with HandBrake (free app)

HandBrake is a free, open-source video transcoder for Mac, Windows and Linux. Version 1.11.2 runs on macOS 10.13 or later.

1. Open HandBrake and drag in your MKV file.
2. Pick a preset, for example one of the Fast or HQ presets at your file’s resolution.
3. Under Summary, set the format to MP4.
4. Choose where to save it and press Start.

HandBrake always re-encodes, so it takes minutes to hours and loses some quality. In exchange it can shrink a large file and convert codecs MP4 cannot hold. If your goal is a smaller file, it is the right tool. If you only want an MP4, the remux above is faster and better.

Method 3: convert MKV to MP4 with VLC

If VLC is already installed, open the File menu and choose Convert / Stream. Drop in the MKV, choose a profile that produces MP4, pick Save as File, and start. VLC re-encodes too, so expect the same trade-off as HandBrake, with fewer settings.

What about online MKV to MP4 converters?

They work for small clips, but most limit file size, and you upload your video to someone else’s server and wait for it to come back. For a film of several gigabytes, the local remux above is faster than the upload alone.

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