Convert MKV to MP4 Online or on Desktop

Make an MP4 copy of an MKV video for a compatible phone, player, editor or upload service. Start with the online converter for a quick file, or use UniConverter Desktop for local batch work and output settings. Because MKV can hold several audio and subtitle tracks, confirm which streams your finished MP4 needs before converting.

Use the desktop workflow when you need more control:

Prepare an MP4 profile for the intended playback device
Select available audio-track options before export
Manage multiple local MKV files in a desktop queue
Keep the original until audio and subtitles are checked

Free Download

Try It Free

Quick Answer

Convert MKV to MP4 by importing the file, choosing MP4 and saving the output. Renaming the extension does not convert it.
When all selected streams are suitable for MP4, remuxing can avoid re-encoding; it is not possible for every source and destination.
H.264 video with AAC audio is a practical compatibility-oriented output choice.
Review the chosen audio language, subtitles and synchronization before deleting the MKV source.

How to Convert MKV to MP4 Online

Step 1

Add the MKV file

Upload your local MKV using Add File or drag and drop. For a long recording or repeated conversions, use the desktop queue. A file that fails to open in the original player may need source troubleshooting before any converter can produce a usable result.

Step 2

Choose MP4 output

Select MP4. If you need explicit control over video codec, audio tracks or output settings, use Desktop Converter. Choose settings for the destination player rather than relying on a filename extension alone.

Step 3

Save and review the MP4

Run conversion and save the MP4. Play a section with dialogue and review any required subtitles. Check both the beginning and the end for audio synchronization, and keep the original MKV until the copy has passed those checks.

How to Convert Local Files to MP4 on Desktop

For broad compatibility, choose an H.264/AAC output profile. Inspect Audio Track before conversion; Keep all audio track(s) and original-audio preservation depend on output compatibility. Check subtitle behavior separately.

Follow the official desktop workflow; the illustrations below show desktop controls rather than the online upload tool.

1. Import local videos

Open UniConverter 18 and select Converter on the Home screen. Use Add Files or Add Folder to build the local video queue. Review the source entries before choosing a shared output profile.

Add video files or a folder in UniConverter 18 Converter. Official desktop guide illustration.

2. Choose MP4 and inspect settings

Open Convert to and choose MP4 under the video formats. For broad compatibility, choose an H.264/AAC output profile. Inspect Audio Track before conversion; Keep all audio track(s) and original-audio preservation depend on output compatibility. Check subtitle behavior separately.

Choose a video output profile in UniConverter 18 Converter. Official desktop guide illustration.

3. Set the folder, convert and review

Choose Save to, then select Convert All. When conversion finishes, open the Finished tab and locate the output. Play a representative file in the destination application before processing more files with the same settings.

Review converted files in the Finished tab. Official desktop guide illustration.

Before you finish: compare the result with the source, check the actual dimensions and file size, and open it in the application where it will be used. Keep the original until these checks pass.

MKV vs MP4: Containers, Tracks and Compatibility

What to compare	Source / need	Output / recommendation
File extension	.mkv	.mp4
Container	Matroska multimedia container	MPEG-4 Part 14 multimedia container
Video and audio	Can contain many codec combinations	Playback depends on the codecs placed inside the MP4
Audio tracks	Often contains multiple languages or mixes	Track support depends on conversion settings and player
Subtitles	May include text or image-based subtitle streams	Not every MKV subtitle type transfers directly
Lossless route	A suitable source may be remuxed	Stream copy preserves selected encoded streams when compatible
Compatibility route	A device may not accept the MKV container or its codecs	H.264/AAC MP4 is a practical delivery choice for many devices
Result checks	Keep the source as the reference	Check language, subtitle behavior, sync and intended playback

References: Workflow and format reference · Additional format guidance

Practical Tips for MKV to MP4

UniConverter free MKV to MP4 converter offers fast, instant and batch processing with impeccable results.

Use Online Conversion for a Quick File

The converter above provides a direct MKV-to-MP4 workflow without installing a desktop application. Upload, choose MP4 and save the result. Use the allowance shown by the tool as the limit for that session. A large recording, multiple files or a need to choose tracks makes the desktop route more practical.

Distinguish Remuxing from Re-encoding

MKV and MP4 are containers rather than fixed picture-quality levels. Remuxing copies compatible encoded streams into a different container; re-encoding generates new compressed streams. A format change is not automatically lossless, and stream copy is not a remedy for a codec that the target device cannot decode.

Choose Audio Deliberately on Desktop

A film, lesson or interview may have several audio tracks. In UniConverter Desktop, inspect the Audio Track menu before converting. The documented Keep all audio track(s) option is useful when appropriate, but whether original audio can pass through depends on format and codec compatibility. Confirm which language plays by default in the actual destination.

Treat Subtitles as a Separate Delivery Choice

Embedded subtitle support differs between containers and players. A text subtitle, an image-based subtitle and a subtitle burned into the picture are different cases. Review the required subtitle method before a large conversion. If the MP4 looks correct but captions are missing, changing only the filename will not restore them.

Organize Multiple MKV Files Locally

Add Files or Add Folder to build a Desktop Converter queue, choose the output and Save to location, then use Convert All. Test one file from the collection first. Sources with different audio languages, subtitle types or dimensions deserve separate checks even when they all end in .mkv.

Verify Compatibility Where It Matters

Open the final MP4 in the phone, TV player, editor or upload service that prompted the conversion. Check dialogue sync near the end of a long file, not only the opening seconds. If a device rejects the result, revisit video and audio codec choices rather than repeatedly converting an unsuitable MP4 profile.

Free Download

MKV to MP4 FAQs

How do I change MKV into MP4?

Use the online converter above, or open UniConverter Desktop, add the MKV in Converter, choose MP4 in Convert to, set the destination and select Convert All. Renaming .mkv to .mp4 changes the label but leaves the underlying container unchanged.

Can I convert MKV to MP4 without losing quality?

A compatible source can be remuxed without re-encoding the selected streams. If the audio or video must be encoded for the destination, the process is different and may change quality. Do not assume every converter or MP4 profile performs stream copy.

What is a free way to remux MKV to MP4?

FFmpeg can copy compatible video and audio streams. For the first video and optional first audio track, an example is: ffmpeg -i input.mkv -map 0:v:0 -map 0:a:0? -c copy output.mp4. It intentionally excludes subtitles and extra tracks. Use re-encoding instead when the selected streams or target player are incompatible.

Will MKV to MP4 preserve every audio track and subtitle?

Not automatically. The output settings, stream types and destination player determine what survives and what plays. In Desktop, review the Audio Track selection, then test the actual MP4. Image-based subtitles or unsupported subtitle streams may require a separate workflow.

Why is my converted MP4 silent?

First play the MKV and confirm it contains a working audio track. Then check the selected audio language and output codec. AAC is a practical compatibility choice for many MP4 playback workflows. An audio passthrough setting is useful only when the destination supports the copied audio codec.

Is an MKV to MP4 converter download better than online conversion?

Desktop conversion suits large local files, queues and more detailed output control. Online conversion suits a quick supported file without installation. Choose according to file size, track requirements and where the file is stored; neither route guarantees that every source codec or subtitle will transfer unchanged.

Why does the MP4 still fail to play after conversion?

MP4 is a container, so the file may still contain a video or audio codec that your player cannot decode. Try an H.264/AAC delivery profile and avoid unnecessary high resolution or unusual frame-rate settings. Also confirm the source itself is complete and playable.

Is MP4 always smaller or better than MKV?

No. Container choice alone does not determine quality or size. A remux can have a similar size; re-encoding can make a larger or smaller file depending on the chosen settings. MP4 is useful when it meets a delivery requirement, while the MKV source remains valuable as the original reference.

“Wondershare Video Converter is hands down one of the best tools I’ve added to my creative toolkit. It’s fast, easy to use, and incredibly powerful. Whether I need to convert large video files into different formats, compress them without losing quality, or even edit and trim clips, this software handles it all with ease.”

— TG

“I have been using Wondershare UniConverter for many years. It has been one of the best ways to download, screen capture and convert videos. It has been my go to for video download and conversion.”

— Alan Horner

“Wondershare has so many assets, not just for downloading media. You can convert to other formats. You can create GIFs and clean up videos. There are way too many assets you can use with WonderShare UniConverter that it's a MUST for any video editor or graphics designer. It's worth every penny.”

— P.rajotte

“Simple to use, music`pic` video` all can edit or convert, Make my work faster and easy”

— gyn

“Over the years, Wondershare Uniconverter has really transformed into a powerhouse of tools. You can download, convert, crop, compress, enhance the quality, remove the background and do ton of other useful ops. We can do it for Video, Audio, and images, either individually or in batches.”

— Sura Mukkavilli

“Wondershare UniConverter has completely exceeded my expectations! The software is incredibly fast, easy to use, and supports a wide range of file formats. I was able to convert large videos in just minutes without losing quality. The interface is clean and intuitive, making it beginner-friendly while still offering advanced features for power users. ”

— CHEUNG SIN LIM

— TG

— Alan Horner