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 →This guide describes format capabilities and settings available in different programs. In WeLoveConvert you select the output format and, for supported images, quality. Codec, bitrate, lossless WebP mode and TIFF page selection are not available in the interface. Compare the result and keep your original.
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
Use the current WeLoveConvert workflow
- 1
Choose the output
Select your MP4 file on the device, continue to configuration and confirm MKV as the destination. Keep an unchanged original.
- 2
Convert locally
Keep the tab open while processing. The engine may download on first use. Large files and unsupported source codecs can fail because browser memory and decoder support vary.
- 3
Download and inspect
Download the completed MKV file and open it in the application that will use it. Check the content, file size and, where relevant, duration, sound, dimensions and transparency. A format change does not guarantee a smaller file.
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 |
Controls available in this converter
Choose the destination container. The site uses an automatic encoding profile; it does not offer manual codec, bitrate, resolution, frame-rate, remux, audio-track or subtitle selection. Test a short source in the actual destination player first. Conversion can lose quality, and not every codec in a supported container can be decoded. Keep the source if you need editing or archival control.
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
The current workflow chooses its encoding profile automatically. You cannot select bitrate, CRF, sample rate, bit depth, channels, remux, subtitle handling or audio tracks here. Keep the original and check the saved output in the destination application; conversion is not guaranteed to be lossless.
Media player selects wrong default track
The current workflow chooses its encoding profile automatically. You cannot select bitrate, CRF, sample rate, bit depth, channels, remux, subtitle handling or audio tracks here. Keep the original and check the saved output in the destination application; conversion is not guaranteed to be lossless.
File size is identical to the MP4
The current workflow chooses its encoding profile automatically. You cannot select bitrate, CRF, sample rate, bit depth, channels, remux, subtitle handling or audio tracks here. Keep the original and check the saved output in the destination application; conversion is not guaranteed to be lossless.
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?
The current workflow chooses its encoding profile automatically. You cannot select bitrate, CRF, sample rate, bit depth, channels, remux, subtitle handling or audio tracks here. Keep the original and check the saved output in the destination application; conversion is not guaranteed to be lossless.
Why convert MP4 to MKV?
The current workflow chooses its encoding profile automatically. You cannot select bitrate, CRF, sample rate, bit depth, channels, remux, subtitle handling or audio tracks here. Keep the original and check the saved output in the destination application; conversion is not guaranteed to be lossless.
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?
The current workflow chooses its encoding profile automatically. You cannot select bitrate, CRF, sample rate, bit depth, channels, remux, subtitle handling or audio tracks here. Keep the original and check the saved output in the destination application; conversion is not guaranteed to be lossless.
Can MKV hold multiple video tracks?
The current workflow chooses its encoding profile automatically. You cannot select bitrate, CRF, sample rate, bit depth, channels, remux, subtitle handling or audio tracks here. Keep the original and check the saved output in the destination application; conversion is not guaranteed to be lossless.
How long does MP4 to MKV conversion take?
The current workflow chooses its encoding profile automatically. You cannot select bitrate, CRF, sample rate, bit depth, channels, remux, subtitle handling or audio tracks here. Keep the original and check the saved output in the destination application; conversion is not guaranteed to be lossless.
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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