How to Convert MP4 to MKV: Complete Guide
MKV (Matroska Video) is the format of choice for media archivists and enthusiasts who need a container that supports virtually any codec, unlimited audio and subtitle tracks, chapter markers, and file attachments. Converting MP4 to MKV is typically a lossless remux operation since MKV supports all codecs found in MP4 files. This guide explains when MKV is the better choice and how to convert effectively.
Try It Now — Free →Advantages of MKV Over MP4
MKV surpasses MP4 in several important areas for media management:
- Unlimited audio tracks - include every language, commentary, and descriptive audio track in a single file
- Advanced subtitle support - ASS/SSA subtitles with custom fonts, colors, positioning, and animation effects
- Attachment support - embed custom fonts needed by subtitles, cover art, and NFO files directly in the container
- Better chapter support - XML-based chapters with nested entries, chapter names in multiple languages, and ordered chapters
- Broader codec support - virtually any video and audio codec can be muxed into MKV, including legacy and experimental codecs
- Segment linking - reference external MKV files for seamless playback of multi-part content without merging files
How to Convert MP4 to MKV Step by Step
- 1
Select Your MP4 File
Choose the MP4 file to convert. Since MKV supports all MP4 codecs (H.264, H.265, AAC), this is almost always a simple remux operation with zero quality loss.
- 2
Choose MKV Output Format
Select MKV (Matroska) as the output format. The converter should detect that remuxing is possible and skip re-encoding for an instant conversion.
- 3
Add Additional Tracks (Optional)
If you have separate audio files (different languages) or subtitle files (.srt, .ass, .ssa), add them during conversion. MKV can bundle all of these into a single file.
- 4
Configure Track Metadata
Set language tags for each audio and subtitle track, mark default tracks, and add track names. This metadata helps media players automatically select the appropriate tracks.
- 5
Convert and Verify
Run the conversion (remux). Verify that all tracks appear correctly in a media player like VLC. Check that default track selection, chapter markers, and metadata are preserved.
MP4 vs MKV: Detailed Comparison
Understanding the differences helps you decide which format best suits your needs.
| Feature | MP4 | MKV |
|---|---|---|
| Audio Track Limit | Multiple (limited player support) | Unlimited (well-supported) |
| Subtitle Types | TX3G, SRT (basic) | ASS/SSA, SRT, PGS, VobSub, WebVTT |
| Font Embedding | Not supported | Full support (for styled subtitles) |
| Chapter Format | Simple markers | Rich XML with nested chapters |
| Codec Flexibility | H.264, H.265, AV1 | Any codec including legacy |
| Lossless Audio | ALAC | FLAC, TrueHD, DTS-HD MA |
| Tagging | iTunes-style tags | Extensive Matroska tags |
Recommended MP4 to MKV Settings
Since MP4 to MKV is typically a remux, settings focus on track management rather than encoding.
MKV supports all codecs found in MP4, so re-encoding is never required. Remuxing preserves perfect quality and completes in seconds.
Mark your preferred audio track as default so media players automatically select it. Use ISO 639-2 language codes (eng, fra, deu, etc.).
Mark the preferred subtitle track as default. Use the "forced" flag for subtitles that should always display (e.g., foreign language dialogue translations).
If the MP4 has chapters, they will be converted to Matroska chapter format. You can also import chapters from an external OGM or XML chapter file.
If using styled ASS/SSA subtitles, attach the required fonts so they render correctly on any system. Add cover art for media library display.
Common MP4 to MKV Conversion Issues
Smart TV or device cannot play the MKV file
MKV has less universal device support than MP4. Check your device specifications for MKV support. Consider keeping an MP4 version for devices that cannot handle MKV.
Subtitle fonts look wrong after conversion
ASS/SSA subtitles use custom fonts. Embed the required font files as attachments in the MKV container so they render correctly on any system.
Media player selects wrong default track
Set the correct default track flags during conversion. Mark only one audio and one subtitle track as default per language.
File size is identical to the MP4
This is expected for a remux. MKV and MP4 have negligible container overhead difference. The video and audio data sizes are identical.
Chapter names are missing
MP4 chapters sometimes lack names. Add chapter names manually using a Matroska editor tool after conversion, or import a chapter file with named entries.
Frequently Asked Questions
Does converting MP4 to MKV lose quality?
No. MP4 to MKV is a remux operation that only changes the container without re-encoding. The video and audio streams are copied bit-for-bit with zero quality loss.
Why convert MP4 to MKV?
MKV offers superior support for multiple audio tracks, advanced subtitles (ASS/SSA), font embedding, rich chapters, and broader codec compatibility. It is the preferred format for media archiving and enthusiast collections.
Will the file size change?
No, the file size will be virtually identical. MKV has slightly more metadata overhead (a few kilobytes) but the audio and video data are copied unchanged.
Can all devices play MKV files?
No. While most modern PCs, Android devices, and many smart TVs support MKV, iOS devices and some older hardware do not. Check your target device compatibility before converting.
How do I add subtitles to the MKV?
During conversion, add external subtitle files (.srt, .ass, .ssa) as additional tracks. Set language tags and default/forced flags for each subtitle track.
Can MKV hold multiple video tracks?
Yes, MKV can contain multiple video tracks, though this is rare in practice. The most common use is a single video track with multiple audio and subtitle tracks.
How long does MP4 to MKV conversion take?
Since it is a remux, conversion takes only seconds regardless of file size. A 10 GB movie file converts in under 30 seconds on modern hardware.
Converting MP4 to MKV is a lossless operation that unlocks the Matroska container superior media management features. Use MKV when you need multiple audio tracks, advanced subtitles, font embedding, or rich chapter support. The conversion is instant and quality-preserving, making it risk-free. Keep MP4 versions for devices that lack MKV support.
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