Free Ways to Compress Big MKV File on Mac/Windows

Diana Joan

Jun 21, 2017 10:19 am / Posted by Diana Joan

MKV is the shortened version of Matroska Video. It gathers multiple types of files, including subtitles files, audio tracks, multiple video tracks, etc. to one file. That is to say, MKV video is usually in much larger file size. And due to its large file size, we may meet some troubles when uploading MKV to certain vidoe sharing sites, and plan to store more MKV movies on our storage device. Sometimes, we even find the screen resolution of our devices do not support the playback of large resolution file size of MKV. So is there any free ways to compress big MKV file to smaller size? Yes, of course there is. Just follow the tutorial below to compress big MKV files with no quality loss.

Part 1: Parameters that affect MKV file size

Part 2: How to Compress MKV Files on Mac/Windows?

Part 3: Optional Free ways to Compress MKV Videos

Part 4: Best MKV Compression Settings for Youtube, Vimeo, Facebook & Instagram

Part 1: Parameters that affect MKV file size

Before compress big MKV file, we need to learn these video parameters that affect video file size, which will help us make sense of the options we have while compressing MKV.

Codec: This is a method that computer uses to decide on the amount of change that occurs between frames.

Keyframe: This is a reference frame. The codec will determine a keyframe every few frames. This is the base frame for the next few frames of change. Your keyframe interval will have a large impact on the size of your MKV file. Lots of keyframes will make the file large but higher quality. Infrequent keyframes will leave lots of artifacts.

Artifacts: These are blocky pieces of image that are the result of the keyframe not being updated correctly. The lower the quality of the compression, the more artifacts that will appear.

Bit/data rate: This is the amount of data that each second of video uses. Typically, this is measured in kilobits per second. Bit rates can be either Constant or Variable. A constant bit rate stays the same throughout the video, which can lead to larger video files. A variable bit rate changes depending on the amount of action on the screen, which will lead to smaller files.

Frame rate: this is the number of frames per second. Videos are typically shot in 24 or 30 frames per second. Keep the compressed copy's frame rate the same otherwise playback will be affected and audio may not sync properly.

Resolution: This is the size of the outputted video. It is measured in pixels, width x height.

Part 2: How to Compress MKV Files on Mac/Windows?

After comprehending these video parameters that affect MKV file size, let's start compress big MKV file to smaller one. As I know, there are mainly two methods to compress MKV video file size:

Method one: Compress MKV by converting MKV to H.264 MP4

With same video quality, MKV file size is much larger than H.264 MP4. To shrink MKV without quality loss, we can convert MKV to H.264 MP4.

Method two: Shrink MKV by adjusting MKV video bit rate, resolution, frame rate, etc.

This method helps to shrink MKV files to achieve a good balance between quality and file size.

To successfully compress big MKV, you can choose method one to change video format, or use the second method to shrink MKV file size. You can also utilize the two methods at the same time to compress video file size.

Then, here comes the question: how to convert MKV to MP4 and how to adjust MKV parameters? Here I highly recommend iMedia Converter for Mac, which is a easy-to-use video converter and compressor for Mac users (support macOS 10.13, macOS Sierra, Mac OS X 10.11 El Capitan, etc). It is capable of converting and compressing 4K/ UHD/1080p large video file like H.265, MKV, XAVC S, MXF, MTS, M2TS, AVCHD, etc. to small file size in the file format of MP4 with H.264 codec. Futhermore, this MKV compressor also provides video editing functions for you to reduce video file size, such as cut out unwanted segments, lower the file resolution or bit rate of the output video, etc.

Apart from compressing common video file, this program also gives you a chance to compress Blu-ray or DVD to your desired file format or device preset profile formats. Here is an equivalent version for Windows: Pavtube Video Converter Ultimate.

How to compress MKV with iMedia Converter for Mac?

Step 1: Load MKV files to the video compressor

Click "File" drop-down option, then select "Add Video/Audio" or "Add from folder" to select the MKV file you want to compress.

load mkv to compressor

Step 2: Define output file format

You can output your MKV video to MP4 format, which is highly compressed with H.264 codec. It is a small video format that has perfect compatibility with many portable devices and media players. Just click on "Format" bar, go to "Common Video", then select "H.264 Video(*.mp4). If your device support H.265 codec, you can also compress MKV to H.265 MP4.

h.264 mp4

Step 3: Adjust output profile parameters

1. Click "Settings" button behind Format bar, to open "Profile Settings" window. You can change output video resolution to 640 x 480, which is more preferable by many portable devices such as iPhone, iPad, Android phone and tablet, etc and video sharing sites like YouTube, Facebook and Vimeo.

2. Lower the bit rate 20-50% of the default to get small files.

3. Trim video file size. Click the "Edit" icon on the UI to open "Video Editor" window. You can cut off the unwanted parts from a long video to short ones by setting the start time and ending time.

h.264 mp4 profile settings

Step 4: Compress MKV file size

Hit on the right-bottom "Convert" button to start compress MKV to smaller video file. After a few minutes, you will get your compressed video with small file size.

Part 3: Optional Free ways to Compress MKV Videos

1. Handbrake for Mac

HandBrake for Mac is a totally free software to compress MKV to MP4 on Mac. But the interface the program is a little complicated. Besides, it only support MP4 and MKV as output container, and the MP4 compression settings is not so multiple.

Handbrake for mac

Compress MKV with Handbrake

1. Launch Handbrake, click the "Source" button to browse and select the large MKV file you desire to compress.

2. Specify a preset for your output profile. Handbrake offers 9 option under the Devices presets including Universal, iPad, iPod, iPhone & iPod touch, Apple TV, etc. Choose one according to your own preference. You can also directly click Format bar to choose MP4 as output format.

3. Click "Browse" and choose the location for your destination. Give your new file a fitting name, and click "Save".

Although Handbrake has gained great popularity as a beneficial MKV compressor. However, when people use Handbrake to shrink MKV video, they still encounter many errors such as no valid source found, video/audio out of syncing or other unexpected issues. If you are facing the same issue mentioned above and find no proper way to fix them effectively, you can try a Hanbrake compressor alternative.

2. Free Video DVD Converter Ultimate

Free Video DVD Converter Ultimate is a free MKV compressor for Windows that allows you to convert video/DVD to AVI, WMV, MPG, MOV, MKV, etc. Meanwhile, it provides similar video editing function as iMedia Converter for Mac, such as trimming, cropping, splitting to help you compress big MKV file to smaller one. Its interface and operation steps is similar to iMedia Converter for Mac and users even can quickly find the options they need without guide. However, this free version can't support MP4 output, if you need convert MKV to MP4, you can just upgrade it or use Pavtube Video Converter Ultimate.

free video dvd converter ultimate load dvd video

Part 4: Best MKV Compression Settings for Youtube, Vimeo, Facebook & Instagram

If you want to compress MKV videos for Youtube, Vimeo, Facebook & Instagram, just follow the table to choose the settings.

Best MKV Compression Settings Youtube Vimeo Facebook Instagram
Container MP4 MP4 MP4/ MOV MP4
Codec H.264 H.264 H.264 H.264
Frame rate The same as the original video 24, 25, or 30 FPS 25-30 fps 29.96 fps
Bit rate 1000 kbps (360p), 2500 kbps (480p), 5000kbps (720p), 8000kbps (1080p), 10Mbps (1440p), 35-35kbps (2160p) 2,000 kbit/s for standard definition (SD) video; 5,000 kbit/s for 720p HD video; or 10,000 kbit/s for 1080p HD video. There is no recommendation for Bitrate as it highly rests upon codec 3,500 kbps
Resolutions 426x240 (240p), 640x360 (360p), 854x480 (480p), 1280x720 (720p), 1920x1080 (1080p), 2560x1440 (1440p), 3840x2160 (2160P) SD video include 640 x 480 px (4:3 aspect ratio) and 640 x 360 px (16:9 aspect ratio). HD video is usually formatted at 720p (1280 x 720 px) or 1080p (1920 x 1080 px). 1280px maximum width 1080 pixels (any height)
Audio codec AAC-LC AAC-LC AAC AAC audio codec at 44.1 kHz mono
Audio bitrates Mono (128 kbps), Stereo (384 kbps), 5.1 (512 kbps) 128 kbps There is no recommendation for Audio Bitrate as it highly rests upon codec 5,500 kbps video bitrate (although Instagram may reduce this to 3,500kbps when we post it)


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