Does an MKV File Compress Video on Its Own?
This article explains the relationship between the MKV file format and video compression. While many people believe that saving a video as an MKV file automatically compresses the footage to reduce its size, MKV is actually a multimedia container rather than a compression codec. Below, we break down how MKV files work, the difference between containers and codecs, and how the video data inside an MKV file is actually compressed.
Containers vs. Codecs
To understand why an MKV file does not compress video on its own, it is important to understand the difference between a container and a codec:
- The Container (MKV): Matroska Video (MKV) is a container format. Think of it as a digital box that holds various tracks of data—such as video, audio, subtitles, and metadata—and packages them into a single file. The container itself does not alter, compress, or decompress the data it holds.
- The Codec (H.264, HEVC, etc.): A codec (compressor/decompressor) is the software or algorithm used to actually shrink the size of the video and audio data. Codecs like H.264, H.265 (HEVC), VP9, and AV1 analyze the raw video frames and compress them so they take up less storage space.
How Video Compression Happens in MKV
When you create or convert a video into an MKV file, the compression is entirely performed by the chosen video codec, not the MKV wrapper.
For example, if you encode a video using the highly efficient H.265 (HEVC) codec and save it as an MKV file, the resulting file will be relatively small because of the H.265 codec’s compression capabilities. Conversely, if you put uncompressed raw video into an MKV container, the file size will remain massive.
The MKV container is highly popular because it is incredibly flexible. It can hold almost any combination of video and audio codecs, multiple audio tracks in different languages, and various subtitle formats (like SRT, SSA, or ASS) all within one file.
Summary
An MKV file does not compress video data on its own. It acts solely as a wrapper to hold video, audio, and subtitle streams together. The actual video compression, which determines the final file size and visual quality, is performed by the specific video codec used to encode the video stream stored inside the MKV container.