MP4
MPEG-4 videoUsed for widely compatible web and device video.
- Family
- Video
- MIME
- video/mp4
Convert MP4 to MKV online
To convert MP4 to MKV, upload the MP4 file, start the conversion and download the result: Converter.now writes an MKV with H.264 video (CRF 23) and Opus audio at 160 kbps. The first video and audio tracks are re-encoded; extra audio tracks and embedded subtitles are not copied. Both formats are lossy, so this adds a second round of compression; convert from the best original you have rather than an earlier export.
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MP4 to MKV at a glance
- Converts
- MPEG-4 video → Matroska video
- Output
- An MKV with H.264 video (CRF 23) and Opus audio at 160 kbps
- Compression
- MP4: lossy → MKV: lossy
- Engine
- FFmpeg
- Privacy
- Private download link; files are deleted after 6 hours. No account needed.
Timed-stream transcoding: How MP4 becomes MKV
Decoding MP4 recovers the picture, sound, and timing streams it carries; writing MKV means re-expressing that under a different codec and container profile. Duration commonly survives untouched even while compression, channel mapping, cadence, metadata, or auxiliary streams do not. MP4 demultiplexing follows track, sample, edit, and fragment tables to inventory codecs, rotation, language, chapters, captions, and synchronization data. Matroska delivery can retain multiple timed tracks, languages, subtitles, chapters, and attachments, though simplified writers and browser players may use only a subset.
Decoded from a broadly supported MPEG-4 container written here with H.264 video and AAC audio when those streams exist. Encoded to a flexible Matroska container capable of multiple audio, video, subtitle, and attachment streams.
For related jobs, compare other MP4 converters with the full list of MKV conversions.
Background reading: why the same extension can hold different codecs covers why a familiar extension can still fail to play.
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MKV
Matroska videoDesigned for flexible multi-track video storage.
- Family
- Video
- MIME
- video/x-matroska
Reading MP4 correctly and satisfying what MKV expects
What can fail when MPEG-4 video is interpreted
An audio-only source does not gain pictures, and ancillary streams such as captions may not carry over.
What Matroska video cannot safely promise
A simplified conversion may keep only primary streams, and many browsers do not play MKV directly.
How the MKV writer handles this route
The verified MKV profile uses H.264 video and Opus audio when those streams are present.
How to confirm the converted MKV actually works
Record the MP4 evidence before conversion
Test playback, seeking, audio sync, dimensions, and whether the expected video stream actually exists.
Test the MKV file in its receiving workflow
Inspect the stream list, subtitles, language labels, chapters, seeking, and sync.
Deciding when MP4 to MKV is the right conversion
Confirm the receiving player, editor, or publishing service actually names MKV's container and codecs before switching; stay with MP4 if extra tracks or original encoding need to survive intact.
What changes between the MP4 model and the MKV deliverable
- The first video and audio tracks are re-encoded; extra audio tracks and embedded subtitles are not copied.
- Both formats are lossy, so this adds a second round of compression; convert from the best original you have rather than an earlier export.
- Treat MP4-specific metadata fields as optional in the MKV result until you have actually confirmed they survived.