Video Conversion

How to Convert MKV to MP4 (Fast Remux — No Quality Loss)

Q: What is the difference between MKV and MP4?

MKV (Matroska Video) and MP4 (MPEG-4 Part 14) are both container formats — they hold video and audio streams but don't compress them. The difference is in what each container supports: MKV supports virtually any codec plus multiple audio tracks, subtitles in any format, chapters, and attachments. MP4 is more restricted but universally supported by devices, TVs, phones, and video platforms.

Q: Does converting MKV to MP4 lose quality?

If you remux (stream copy) — no quality loss at all. Since both MKV and MP4 are containers, and the video codec inside is usually H.264 which both support natively, you can copy the streams from MKV into an MP4 container without touching the video or audio data. The result is identical quality, and the process takes seconds regardless of file size.

Q: Why is my MKV file not playing on my TV?

Most smart TVs support MP4 (H.264) natively but not MKV. While many modern TVs do support MKV playback, compatibility varies by manufacturer and firmware version. Converting to MP4 ensures playback on virtually any device including Chromecast, Roku, Apple TV, and smart TVs. The remux process doesn't change the video quality.

Q: How long does MKV to MP4 conversion take?

With stream copy (remux), conversion time depends only on disk read/write speed — not video length. A 10GB MKV file typically converts in 10–30 seconds on a modern computer. If re-encoding is required (when the MKV contains codecs MP4 doesn't support), conversion time is proportional to video length and quality settings — potentially 10–60 minutes for a feature film.

Q: What if my MKV has subtitles I want to keep?

MP4 supports subtitles but only in MOV_TEXT or TTML format, not the ASS/SSA format common in MKV fansubs. When remuxing, use FFmpeg: ffmpeg -i input.mkv -c:v copy -c:a copy -c:s mov_text output.mp4. If the subtitles are ASS/SSA, convert them to SRT first, or keep them as a separate .srt file alongside the MP4.

May 18, 2026 · 8 min read · Convertlo Team

The most important thing to understand about converting MKV to MP4: it usually isn't a conversion at all — it's a remux. Both MKV and MP4 are container formats. The video codec inside the MKV (almost always H.264) is natively supported by MP4. So converting means moving the same video and audio data from one container to another, with zero re-encoding and zero quality loss. A 20GB MKV file converts in about 30 seconds.

The key insight: MKV and MP4 are just different boxes. If the video inside the box (usually H.264) fits in both, you're just switching boxes — instant, lossless.

MKV vs MP4: What's Actually Different

MKV (Matroska Video) and MP4 (MPEG-4 Part 14) are container formats — they organize and package video, audio, and subtitle streams into a single file. The container doesn't compress the video; the codec inside does.

Feature	MKV	MP4
Open standard	Yes (Matroska)	Yes (MPEG-4)
Supported codecs	Any (H.264, H.265, AV1, VP9, etc.)	H.264, H.265, AV1 (limited)
Multiple audio tracks	Yes (unlimited)	Yes (limited support)
Subtitle formats	ASS, SSA, SRT, PGS, and more	MOV_TEXT, TTML (SRT with limits)
Chapter markers	Native	Yes
Device compatibility	Good (VLC, modern TVs)	Universal (every device)
Web browser playback	Limited	Universal HTML5 video
iPhone / iPad playback	No (native)	Yes
Upload to YouTube	Supported	Preferred

Method 1: FFmpeg Remux (Fastest, Zero Quality Loss)

This is the correct and fastest method for the vast majority of MKV files:

ffmpeg -i input.mkv -c:v copy -c:a copy output.mp4

What this does:

-c:v copy — copy the video stream without re-encoding
-c:a copy — copy the audio stream without re-encoding
Result: identical video and audio, just in an MP4 container
Speed: limited only by disk read/write speed, typically 30 seconds for a 10GB file

If you get an error about the audio codec (some MKV files use audio codecs MP4 doesn't support), fix it by re-encoding only the audio:

ffmpeg -i input.mkv -c:v copy -c:a aac -b:a 192k output.mp4

This copies the video losslessly but converts audio to AAC at 192kbps — still very fast since only audio is re-encoded.

Method 2: VLC Media Player (Free, GUI)

Open VLC → Media → Convert/Save (or Ctrl+R)
Click Add → select your .mkv file → click Convert/Save
In the Profile dropdown, select "Video - H.264 + MP3 (MP4)" or "Video - H.265 + MP3 (MP4)"
Click the wrench icon next to Profile → Video Codec → Encoding tab → check "Keep original video track" (for remux)
Set destination file with .mp4 extension → click Start

VLC's convert function re-encodes by default unless you configure the "keep original track" option. For large files, FFmpeg's stream copy is faster and cleaner.

Convert MKV to MP4 Online

No FFmpeg install? Convert your MKV files directly in the browser — free, no upload to external servers.

Convert MKV → MP4 All Video Converters

When Re-encoding IS Required

The stream-copy method works when the MKV's video codec is compatible with MP4. It fails when:

Video codec is VP8 or VP9: MP4 doesn't support these natively. Re-encoding to H.264 is required.
Audio codec is FLAC or DTS: MP4 doesn't support FLAC audio or raw DTS. Re-encode to AAC.
Subtitles are ASS/SSA format: MP4 subtitle support is limited. Extract as .srt or burn in.

To check what codecs your MKV contains before converting:

ffprobe -v quiet -print_format json -show_streams input.mkv

Look at the codec_name fields. If video is h264 or hevc and audio is aac or ac3, stream copy will work perfectly.

MKV to MP4 for Specific Platforms

iPhone / iPad: MP4 H.264, max 60fps, AAC audio. Use stream copy if source is already H.264.
PS4 / PS5: MP4 H.264 or H.265, AAC audio. Stream copy works for most MKVs.
Samsung Smart TV: MP4 H.264/H.265, AAC/AC3 audio. Most MKV content remuxes fine.
YouTube upload: MP4 H.264, AAC stereo. Use -c:v copy -c:a aac for safe uploads.

Frequently Asked Questions

What is the difference between MKV and MP4?

Both are container formats that hold video and audio streams. MKV supports more codecs and features (multiple audio tracks, ASS subtitles, any codec). MP4 has universal device compatibility — every phone, TV, browser, and platform supports MP4. Converting between them when the codecs are compatible is instant and lossless.

Does converting MKV to MP4 lose quality?

No, if you remux (stream copy). Since H.264 video works in both containers, you copy the exact same video data into the MP4 container. Zero quality loss, near-instant conversion. Only re-encoding (when codecs are incompatible) loses quality.

Why is my MKV file not playing on my TV?

Most smart TVs support MP4 H.264 natively but MKV compatibility varies by manufacturer. Converting to MP4 ensures playback on virtually any device without quality loss — the remux takes seconds and the result is identical quality.

How long does MKV to MP4 conversion take?

With stream copy (remux), a 10GB MKV file converts in 10–30 seconds on a modern computer — limited by disk speed, not processing. Re-encoding takes proportionally longer: a 2-hour film re-encodes in 10–60 minutes depending on quality settings and CPU/GPU.

What if my MKV has subtitles I want to keep?

Use: ffmpeg -i input.mkv -c:v copy -c:a copy -c:s mov_text output.mp4. If subtitles are ASS/SSA format (common in fansubs), convert them to SRT first or keep them as a separate .srt file alongside the MP4.