Compress MKV Video
Reduce the file size of your MKV videos by optimizing codec, quality, and resolution while maintaining visual quality.
Compress MKV files online, no account needed
SimpleSize encodes your MKV at a lower bitrate and, optionally, a reduced resolution, then returns a smaller MKV file. The container format stays MKV throughout. Nothing is converted to a different format unless you choose to do that separately. Files up to 1 GB are accepted, and no login is required.
Processing runs server-side, so your device's CPU and RAM are not involved. A real-time progress bar shows elapsed time, total duration, time remaining, and completion percentage while the job runs.
Why MKV file size matters
MKV (Matroska) is a flexible container that can hold virtually any video or audio codec, multiple subtitle tracks, and chapter markers. That flexibility makes it popular for archiving and home media, but the resulting files are often large. A single 4K MKV can exceed several gigabytes, which creates friction when sharing, uploading to cloud storage, or moving files between devices.
Reducing the bitrate through re-encoding is the most effective way to shrink an MKV. Unlike simply changing the container, re-encoding actually discards redundant visual data the encoder judges to be imperceptible, which is where the real size savings come from.
Codec and quality options explained
When you compress a MKV file here, you choose how the video data is re-encoded. The tool offers five codecs:
- VP9 (default): Good compression efficiency with broad software player support. A reliable starting point for most MKV files.
- VP8 : An older codec with slightly less compression efficiency than VP9, but faster to encode.
- H.264 : Widely compatible, hardware-accelerated on most devices, and well-supported in media players.
- H.265 : Higher compression efficiency than H.264 at the same visual quality, but requires more processing time and a compatible player.
- AV1 : The most efficient codec available here, producing the smallest files, but also the slowest to encode.
The quality slider runs from 10% to 100% (default 70%). This percentage sets the target bitrate relative to the original. At 70%, the encoder aims for roughly 70% of the source bitrate, which typically yields noticeable size savings with acceptable visual quality. Lower values shrink the file further but introduce more visible compression artifacts.
The target resolution lets you output at the original height or scale down to 2160p, 1440p, 1080p, 720p, or 480p. Scaling down multiplies the size reduction on top of whatever the bitrate setting achieves. To understand how bitrate and quality interact, see the video bitrate guide .
How to use the MKV compressor: Step by step
- Open the tool at this page. You can also reach it from the Video tab on the video compressor page.
- Drag your MKV onto the dropzone, or click to browse your files. The file uploads and the tool prepares it for encoding.
- Select a codec from the dropdown. VP9 is the default and works well for most files.
- Adjust the quality slider. A value between 50% and 75% is a practical range for reducing size while keeping the video watchable.
- Optionally choose a target resolution if you want to reduce the frame dimensions as well.
- Click "Compress Video". The progress bar tracks the job in real time.
- When the job finishes, review the results: original size, compressed size, savings percentage, codec used, and output bitrate. Click the download button to save your file. The download link expires after 300 seconds, so download promptly.
The tool processes up to 10 videos per IP address per day, with the count resetting at midnight UTC. This limit is shared with the video converter on the same account.
When to use this tool and when to use something else
This MKV file compressor is the right choice when you need a smaller file and want to keep the MKV container. Common scenarios include:
- Reducing archive files before uploading to cloud storage
- Shrinking large recordings to fit within email or messaging attachment limits
- Lowering bitrate before sharing via services that re-encode anyway, to preserve more control over quality
- Scaling down 4K or 1440p footage you recorded but only need at 1080p or 720p
MKV is an excellent archiving container, but it is not universally supported on phones, smart TVs, or web browsers. If broad playback compatibility matters more than keeping the MKV format, use the video converter to produce an MP4 instead. For other video formats, the MP4 compressor and MOV compressor follow the same workflow.
FAQ
The tool re-encodes the video stream inside your MKV using the codec and quality settings you choose. Re-encoding works by analyzing each frame and discarding visual information the encoder judges as imperceptible, then storing the remaining data more efficiently. The output is a new MKV file with a lower bitrate. The container format stays MKV; only the encoded content inside it changes.
AV1 produces the smallest files at a given quality level because it uses more sophisticated prediction and entropy coding than older codecs. However, it takes the longest to encode. H.265 is a practical middle ground: meaningfully more efficient than H.264, with reasonable encoding time. If you need the output to play on older hardware or software without issues, H.264 offers the widest compatibility. VP9 (the default) balances efficiency and encoding speed well for most use cases. See what is a codec for a deeper explanation.
The slider sets the target bitrate as a percentage of the original. The default of 70% is a reasonable starting point that reduces file size noticeably for most videos without introducing obvious visual degradation. Values below 50% will shrink the file further but may produce visible blocking or blurring, especially in fast-motion scenes. Values above 80% yield smaller savings but preserve more fine detail. The right value depends on your source material and how closely the output will be scrutinized.
The tool accepts MKV files up to 1 GB. If your file exceeds that limit, consider reducing the resolution or trimming the video in a local editor before uploading. You can also process the file in segments if your editor supports splitting. The daily limit is 10 video jobs per IP address, shared across video compression and conversion, resetting at midnight UTC.
Yes. The output container always matches the input. When you upload an MKV, you get an MKV back. This tool does not convert between container formats. If you need the video in a different format, such as MP4 for broader device compatibility, use the video converter after or instead of compressing.
Compressing re-encodes the video stream at a lower bitrate while keeping the same container format. The goal is a smaller file of the same type. Converting remuxes or re-encodes the content into a different container, such as changing MKV to MP4. Converting to MP4 does not necessarily reduce file size on its own; it primarily changes which players and platforms can open the file. You can do both operations together by converting and setting quality options at the same time.
Yes, and the effect is significant. Scaling from 4K (2160p) to 1080p reduces the total pixel count by 75%, which means the encoder has far less visual data to store per frame. Combined with a lower quality setting, downscaling produces the largest file size reductions. If you do not need the original resolution for your use case, choosing a lower target resolution is one of the most effective ways to shrink an MKV.
Uploaded files and compressed outputs are stored temporarily on the server only long enough to complete processing and allow download. The download link expires after 300 seconds. Files are not retained for training, analysis, or any other purpose beyond completing your requested job. For full details on data handling, see the privacy policy .
This can happen when the source video was already heavily compressed or encoded at a low bitrate. Re-encoding introduces a new generation of encoding decisions on top of an already compressed signal, which can increase the bitrate if the encoder struggles to represent the existing artifacts efficiently. It can also happen if you choose a higher quality percentage than the original was encoded at. Try lowering the quality slider or choosing a more efficient codec such as H.265 or AV1.
HDR MKV files can be uploaded. The tool includes a convert HDR option that tone-maps HDR content to standard dynamic range during encoding. If you leave this option off and encode HDR content with a codec that does not carry HDR metadata through the new encode, the output may display with washed-out colors on SDR displays. Enabling the HDR conversion option avoids this by mapping the HDR luminance range into the SDR range during re-encoding.
The tool is free to use with no account or subscription required. The limit is 10 video jobs per IP address per day, shared across video compression and conversion. The counter resets at midnight UTC. There is no limit on the number of image or audio jobs. If you need to process more than 10 videos in a single day, you would need to wait for the reset or use a different network connection.