What is the difference between MKV and MP4?

MKV (Matroska) is an open-source container designed to hold almost any combination of video, audio, subtitles, and chapters. It is highly flexible but not universally supported. MP4 (MPEG-4 Part 14) is the industry standard supported by every browser, phone, streaming service, and editing application. For sharing or playback compatibility, MP4 is almost always the right choice.

Will converting MKV to MP4 lose quality?

Not if you use stream copy (-c copy). When the MKV already contains H.264 video and AAC or MP3 audio, FFmpeg simply moves the data into an MP4 container without touching the encoded frames — zero quality loss and very fast. Re-encoding is only needed when the video codec is H.265, VP9, or AV1, or when the audio codec (Opus, Vorbis, AC3) is not MP4-compatible.

How do I install FFmpeg?

On Mac, run: brew install ffmpeg. On Windows, run: winget install ffmpeg (or download the build from ffmpeg.org). On Ubuntu/Debian Linux, run: sudo apt install ffmpeg. Once installed, the ffmpeg command is available in any terminal.

What CRF value should I use?

CRF (Constant Rate Factor) controls quality for H.264 and H.265. For H.264: CRF 18 is near-lossless, CRF 23 is the default (good balance), CRF 28 gives smaller files with some visible quality loss. For H.265 (HEVC): CRF 24–28 gives equivalent quality to H.264 at roughly half the file size. Use CRF 18–20 for archival, CRF 22–24 for sharing.

What does -movflags +faststart do?

It moves the MP4 index (moov atom) to the beginning of the file. This allows the video to start playing in a browser or streaming service before the entire file is downloaded. Always use it when producing MP4 files for the web.

Why does my converted MP4 have no audio?

MKV files often carry Opus, Vorbis, or AC3 audio which MP4 does not support. Select "Re-encode to AAC" for the audio option and FFmpeg will transcode the audio track to AAC, which is universally compatible with MP4.

Can I convert multiple MKV files at once?

Yes. On Linux/Mac, use a shell loop: for f in *.mkv; do ffmpeg -i "$f" -c:v copy -c:a aac "${f%.mkv}.mp4"; done. On Windows PowerShell: Get-ChildItem *.mkv | ForEach-Object { ffmpeg -i $_.Name -c:v copy -c:a aac ($_.BaseName + \".mp4\") }. The generated command on this page serves as the template for each file.

Why is the conversion very slow?

Stream copy (-c copy) is almost instant. Slow conversions mean re-encoding is happening. To speed it up, use a faster preset (-preset fast or -preset ultrafast) at the cost of a slightly larger output file, or enable hardware acceleration: -c:v h264_nvenc for Nvidia GPUs, -c:v h264_videotoolbox on Mac, or -c:v h264_qsv for Intel Quick Sync.

MKV to MP4 Converter

Name: MKV to MP4 Converter
Availability: InStock
Author: Nham Vu

Generate a ready-to-run FFmpeg command to convert your MKV file to MP4 — choose codecs, quality, and audio settings, then copy the command to your terminal.

FFmpeg Command Generator

Fill in the options below and get the exact command to paste in your terminal.

Input filename

Include the path if the file is not in the current directory, e.g. ~/Downloads/movie.mkv

Output filename

Video handling

Quality (CRF) — 23 (lower = better quality, larger file)

0 — lossless 23 — default 51 — worst

Encoding preset

Audio handling

Add -movflags +faststart

Recommended for web/streaming — moves the MP4 index to the start of the file so playback begins before the full file downloads.

Copy subtitle tracks

Include -c:s mov_text to copy embedded MKV subtitles as MP4-compatible text subtitles (SRT-style). Not supported by all players.

Generated FFmpeg Command

ffmpeg -i input.mkv -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 192k -movflags +faststart output.mp4

Click the command to select all, then copy. Run it in any terminal where FFmpeg is installed.

Command Breakdown

Flag	What it does

MKV vs. MP4 — Format Comparison

Understand what you are converting and why

Feature	MKV	MP4
Origin	Open source, Matroska (2002)	MPEG group / ISO (2001)
Common codecs	H.264, H.265, VP9, AV1, Opus, Vorbis	H.264, H.265, AV1, AAC, MP3
Browser support	Limited (Chrome only, not Safari)	Universal — all browsers
iOS / Apple TV	Not supported natively	Full native support
Streaming (faststart)	Not supported	Supported
Subtitle tracks	Excellent (ASS, SSA, SRT)	Basic (mov_text / SRT only)
Multiple audio tracks	Excellent	Supported

FFmpeg Installation

One command per platform — free and open source

# macOS (Homebrew)
brew install ffmpeg

# Windows (winget)
winget install ffmpeg

# Ubuntu / Debian
sudo apt install ffmpeg

# Fedora / RHEL
sudo dnf install ffmpeg

Command copied!

Summary

Generate a ready-to-run FFmpeg command to convert your MKV file to MP4 — choose codecs, quality, and audio settings, then copy the command to your terminal.

How it works

Enter your MKV filename (e.g. movie.mkv) in the filename field.
Choose the video codec strategy: fast rewrap (stream copy) or re-encode to H.264 or H.265.
Select your audio handling: copy existing tracks, re-encode to AAC, or strip audio.
Adjust the quality slider (CRF) and optional advanced flags as needed.
Click "Generate Command" to produce the FFmpeg command.
Copy the command and run it in any terminal where FFmpeg is installed.

Use cases

Remux MKV files that already contain H.264/AAC to MP4 with zero quality loss in seconds.
Make MKV movies and TV episodes playable on iPhones, Apple TV, and other iOS devices.
Upload MKV recordings to YouTube, Instagram, or Vimeo which prefer MP4 input.
Convert MKV files for editing in Final Cut Pro or Adobe Premiere that require MP4 containers.
Reduce MKV file size by re-encoding to H.264 with a higher CRF value.
Convert MKV files with Opus or Vorbis audio to AAC for broad device compatibility.
Add the -movflags +faststart flag for web-optimized MP4 files that begin playing immediately.
Batch-convert a folder of MKV episodes to MP4 using the generated command as a template.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu