# How to convert MKV to MP4 on a Mac (free and lossless) > Convert MKV to MP4 on Mac in seconds without losing quality. Learn how to remux with ffmpeg, tag HEVC for QuickTime, or convert using HandBrake. Published 2026-10-16 · Formats & codecs · https://www.hazenstudio.com/maclc/blog/mkv-to-mp4-on-mac/ ## In short - Remuxing changes an MKV container to MP4 without re-encoding: no quality loss, and about as long as copying the file. - The open-source FFmpeg tool copies video and audio tracks directly with the -c copy option. - Adding the -tag:v hvc1 flag is mandatory when remuxing HEVC video, or QuickTime Player will refuse to open the resulting MP4. - MP4 containers cannot hold stylized ASS anime subtitles, Blu-ray PGS bitmaps, or embedded font attachments. - Re-encoding with HandBrake is only required when changing video codecs or burning unsupported subtitles into the image. To convert an MKV to MP4 on a Mac without losing quality, you should remux the file instead of re-encoding it. Using a free command-line tool like FFmpeg, you can extract the original video and audio bitstreams and repackage them into an MP4 container, usually in seconds to a minute or two, without degrading image quality. Many Mac users search for an MKV to MP4 converter because macOS QuickTime Player and Apple mobile devices reject the Matroska (`.mkv`) container. Unfortunately, most commercial converter utilities and online websites do not simply change the container. Instead, they force the video through a slow, lossy re-encoding process that drains your laptop battery, generates heat, and degrades sharp detail. This guide explains how remuxing works, how to run FFmpeg on macOS, how to avoid common QuickTime playback bugs, and when you can skip conversion entirely. ## What is the difference between remuxing and re-encoding? Understanding how to convert MKV files cleanly requires distinguishing between a media container and a video codec. A container is a digital file envelope (such as `.mkv` or `.mp4`). Inside that envelope reside the compressed video stream (such as H.264 or HEVC), audio tracks (such as AAC or AC-3), subtitles, and chapter markers. When you convert a video file, you have two fundamentally different paths: * **Remuxing (Stream Copying):** Remuxing opens the Matroska container, extracts the existing video and audio tracks, and places them into an MP4 container without touching the compressed data. Because no mathematical decompression or recompression occurs, the process is 100% lossless. It runs at the speed of your Mac's storage, so it takes about as long as copying the file. * **Re-encoding (Transcoding):** Re-encoding decodes every compressed frame of the video into raw, uncompressed pixels, and then runs those pixels through a compression encoder (such as `x264` or `x265`). This process causes generation loss, reducing fine detail, smoothing out film grain, and introducing compression artifacts. It also demands intensive CPU and GPU power, often taking from twenty minutes to several hours depending on your Mac's processor. Whenever your source MKV file contains video and audio formats that the MP4 specification supports—such as H.264 or HEVC video paired with AAC or Dolby Digital audio—remuxing is always the superior choice. ## How to install FFmpeg on macOS with Homebrew The industry standard tool for remuxing media streams is FFmpeg, a free and open-source command-line framework used by major media companies, streaming platforms, and software developers worldwide. The most reliable way to install FFmpeg on macOS is through Homebrew, the open-source package manager for Mac. ### Step 1: Open Terminal Press **Command-Space** to open Spotlight, type `Terminal`, and press **Return**. ### Step 2: Install Homebrew (if not already installed) If you do not have Homebrew installed on your Mac, paste the following command into Terminal and press **Return**: ```bash /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" ``` Follow the on-screen prompts. Homebrew will ask for your Mac administrator password to complete the setup. On Apple Silicon Macs, follow the final terminal instructions to add Homebrew to your shell environment path. ### Step 3: Install FFmpeg Once Homebrew is installed, run this command in Terminal: ```bash brew install ffmpeg ``` Homebrew downloads a ready-built FFmpeg along with the libraries it needs. You can confirm the installation by running `ffmpeg -version`, which prints the installed build information. ## How to remux MKV to MP4 in seconds using FFmpeg Once FFmpeg is installed, remuxing an MKV file into an MP4 file requires a single terminal command. Navigate to the folder containing your video file using the `cd` command (for example, `cd ~/Movies`), or type the command and drag your video file directly into the Terminal window to insert its path. The standard command to remux an MKV file to MP4, keeping the video and every audio track, is: ```bash ffmpeg -i movie.mkv -map 0:v:0 -map 0:a -c copy movie.mp4 ``` The interactive diagram below breaks down what each argument in this command instructs FFmpeg to do: *FFmpeg Remux Command Anatomy* Understanding these options helps you avoid the common pitfalls of command-line remuxing: 1. **Why `-map` matters:** by default, FFmpeg picks just one video, one audio and one subtitle stream. If your MKV contains several audio languages or a commentary track, the `-map 0:a` option keeps all of them. 2. **Why `-c copy` prevents quality loss:** it sets every stream to copy mode, so FFmpeg moves the compressed packets from the Matroska file into the MP4 without decoding or encoding anything. 3. **Why subtitles are left out:** MP4 can't hold SubRip (`.srt`) or ASS text as they are, nor bitmap (PGS) subtitles at all, and copying them makes FFmpeg stop with an error. If the file only has text subtitles, you can keep them by converting them to MP4's own text format, 3GPP Timed Text (`mov_text`): ```bash ffmpeg -i movie.mkv -map 0:v:0 -map 0:a -map 0:s -c copy -c:s mov_text movie.mp4 ``` If that fails because one of the subtitle tracks is a PGS bitmap, pick the text tracks by number instead (`-map 0:s:0` for the first one). ## How to fix the HEVC QuickTime bug with the hvc1 tag If your source MKV file contains 4K video compressed with High Efficiency Video Coding (HEVC / H.265), you will often encounter a frustrating issue: FFmpeg finishes remuxing without errors, but QuickTime Player refuses to open the resulting MP4 file or displays a solid black screen. This occurs because the MP4 container specification permits two different FourCC (Four-Character Code) identifiers for HEVC video: `hev1` and `hvc1`. * With `hev1`, the codec's parameter sets (VPS, SPS and PPS) may travel inside the video stream itself. FFmpeg uses `hev1` by default. * Apple's AVFoundation framework, which powers QuickTime Player, Quick Look and iOS apps, expects `hvc1`, where the parameter sets sit in the file's header (the `hvcC` box). When QuickTime finds an MP4 tagged `hev1`, it refuses to play it. To ensure your remuxed MP4 opens in QuickTime Player and across all Apple devices, you must explicitly instruct FFmpeg to write the `hvc1` tag using `-tag:v hvc1`: ```bash ffmpeg -i movie.mkv -map 0:v:0 -map 0:a -c copy -tag:v hvc1 movie.mp4 ``` This single flag resolves the QuickTime compatibility block without requiring any re-encoding. For a deeper look at codec differences across containers, read our guide on [H.264 vs HEVC vs AV1 on Mac](/maclc/blog/h264-vs-h265-vs-av1/). ## What features are lost when converting MKV to MP4? While remuxing to MP4 makes files compatible with Apple's native applications, the MP4 container format has structural limitations compared to Matroska: * **Stylized SubStation Alpha (ASS) subtitles:** Anime releases and foreign cinema frequently use `.ass` subtitle files to display stylized typography, on-screen translations positioned over background signs, and karaoke timing. The MP4 container cannot store ASS styling. If you remux an ASS subtitle track to `mov_text`, all color formatting, font sizing, and screen positioning are permanently stripped, leaving plain text centered at the bottom of the screen. * **Blu-ray Presentation Graphic Stream (PGS) subtitles:** Ultra HD Blu-ray disc rips store subtitles as bitmap images (`.sup` or PGS) rather than text characters. The MP4 container does not support bitmap subtitle streams. FFmpeg cannot convert PGS subtitles into `mov_text` because image bitmaps contain no text data without Optical Character Recognition (OCR). To keep PGS subtitles in an MP4 file, you must burn them into the video frames during a full re-encode. * **Embedded font attachments:** Matroska allows fonts (`.ttf` or `.otf`) to be embedded directly inside the file container via its EBML Attachments element (EBML ID `0x1941A469`). MP4 has no standardized font attachment architecture, meaning custom fonts cannot travel with the file. * **DTS and TrueHD audio:** if your MKV carries DTS (such as DTS-HD Master Audio) or Dolby TrueHD, Apple's apps can't play it even inside an MP4, because macOS has no decoder for either. Convert just that track while copying the video: `-c:v copy -c:a aac` for stereo-friendly AAC, or `-c:a ac3` to keep 5.1 as Dolby Digital. To review these container specifications side by side, read our complete analysis of [MKV vs MP4 on Mac](/maclc/blog/mkv-vs-mp4/). ## When should you re-encode with HandBrake instead? Remuxing works only when the elementary video and audio streams inside your MKV file are already compatible with the MP4 container and your playback software. You will need to re-encode the file using transcoding software if: 1. The video stream uses VP9 or an older codec that QuickTime can't play. 2. The video contains PGS bitmap subtitles that you must hardcode (burn) into the picture for playback on a device that does not support subtitle tracks. 3. You need to reduce the physical file size to fit onto a small USB drive or send over email. When re-encoding is necessary, the best free tool for macOS is HandBrake: 1. Download and install HandBrake from its official project site. 2. Open your `.mkv` file. HandBrake will scan the file's streams and chapters. 3. Under the **Summary** tab, ensure the format is set to **MP4**. Check the box for **Web Optimized** if you intend to stream the video over a network. 4. Under the **Dimensions** tab, verify that the resolution matches your source file. 5. Under the **Video** tab, select **H.265 (VideoToolbox)** as the Video Encoder. Apple's hardware encoder in your Mac's media engine is much faster than software encoders and keeps your laptop cool, at some cost in efficiency. 6. Under the **Subtitles** tab, select your preferred subtitle track and check the **Burn-in** option if you are converting bitmap PGS subtitles. 7. Click **Start** in the toolbar to begin the encoding queue. ## Why should you avoid free online file converters? When searching for "mkv to mp4" on Google, the first page of search results is dominated by free cloud conversion websites. While these tools appear convenient because they do not require using Terminal, using them introduces severe practical and privacy problems: * **File size limits:** many free converters cap uploads well below the size of a film. A 1080p movie is often 4 GB to 8 GB, and a 4K film 15 GB to 50 GB. * **Lossy re-encoding:** most online converters re-encode rather than remux, often at low bitrates, which crushes shadow detail and blurs the image. * **Severe privacy and security risks:** When you use an online converter, you upload your video file to a remote commercial server. If you are converting personal family home videos, legal recordings, or confidential business screencasts, uploading those files to third-party web platforms exposes your private data to potential breaches, automated scraping, or permanent server retention. Installing FFmpeg locally on your Mac takes two minutes, operates entirely offline, handles files of any size, and never uploads a single byte of your media. ## Do you really need to convert your MKV files? Before spending time remuxing or re-encoding dozens of video files, consider whether you need to convert them at all. The only reason to convert an MKV to MP4 is if you are forced to use an application that cannot read Matroska, such as QuickTime Player or Final Cut Pro. If your objective is simply to watch your movies and television shows on your Mac, converting files is unnecessary work. Modern video players designed for Apple Silicon handle Matroska files natively, decoding original video streams, multi-language audio, and stylized subtitles without any file conversion. MacLC, the player we make at Hazen Studio, plays MKV files directly on Apple Silicon Macs running macOS 26 Tahoe or later. It is a fork of VLC 4.0, with everything it needs inside the app, in a native macOS AppKit interface. MacLC opens the MKV as it is: every audio track (DTS and TrueHD included), every subtitle (styled ASS and PGS included), every chapter, with HDR at your screen's full brightness. Nothing to convert, nothing to install. Instead of keeping duplicate MP4 copies of your movies, open your MKVs directly in MacLC, with HDR on Liquid Retina XDR screens, DTS and TrueHD surround mixed down for your speakers, and subtitle timing you can fix on the fly with H and J. To learn how to configure macOS so your MKV files open in a dedicated player automatically, see our step-by-step walkthrough on [how to play MKV files on a Mac](/maclc/blog/how-to-play-mkv-on-mac/), or download the free player directly from our [download page](/maclc/donate/). ## Questions people ask ### What is the fastest way to convert MKV to MP4 on a Mac? The fastest method is remuxing with FFmpeg in Terminal. Running `ffmpeg -i input.mkv -map 0:v:0 -map 0:a -c copy output.mp4` repackages the video and audio tracks into an MP4 container without recompressing anything, usually in seconds to a minute or two. ### Does converting MKV to MP4 reduce video quality? Remuxing causes zero quality loss because the video bitstream is copied byte-for-byte into the new container. However, if you re-encode the file using HandBrake, an online converter, or commercial conversion software, the video is recompressed, which permanently degrades image detail. ### Why won't QuickTime open an MP4 file converted from MKV? If the source MKV used the HEVC (H.265) codec, FFmpeg defaults to the FourCC container tag `hev1`. Apple's AVFoundation and QuickTime Player expect the tag `hvc1` and refuse `hev1`. Adding `-tag:v hvc1` to your FFmpeg command fixes this issue immediately. ### Can I convert MKV to MP4 using QuickTime Player? No. QuickTime Player cannot demux or read Matroska (.mkv) files. Because QuickTime cannot open the original file, it cannot export or convert it to MP4. ### Are free online MKV to MP4 converters safe? Free online converters are risky for personal videos because they upload your files to someone else's server. Many also limit file sizes and re-encode videos at low bitrates, which visibly reduces picture quality. --- MacLC is a free, open-source video player for Apple Silicon Macs: https://www.hazenstudio.com/maclc/ · download: https://www.hazenstudio.com/maclc/donate/