What makes MKV different
MKV (Matroska) is an open container that can hold almost anything: H.264, H.265 (HEVC), VP9 or AV1 video, AAC, Dolby Digital, DTS, FLAC or Opus sound, several audio languages, subtitle tracks and chapters, all in one file. That flexibility is why MKV is popular for films and series, for DVD and Blu-ray backups made with tools like MakeMKV, and for recordings from OBS Studio, where MKV is chosen because the file stays readable even if the computer crashes during recording.
The same flexibility causes problems. Many devices and programs support only part of what MKV can contain, or do not support the container at all.
Where MKV does not work
- Apple devices: the iPhone Photos app, QuickTime Player, iMovie and Final Cut Pro do not open MKV.
- Video editors: Premiere Pro has limited MKV support, and many simpler editors refuse it.
- Social media and messaging apps: most upload forms expect MP4 or MOV.
- TVs and consoles: many play MKV, but some fail on DTS sound, HEVC video or image-based subtitles.
Fast copy or full conversion
Because MKV often already contains modern codecs, many conversions do not need re-encoding at all. The converter checks the tracks and copies them into the new container whenever they fit. This is almost instant and lossless.
| Target | Quick copy when the MKV has | Otherwise |
|---|---|---|
| MP4, MOV | H.264 or HEVC video with AAC sound | Re-encoded to H.264 and AAC |
| WEBM | VP8, VP9 or AV1 with Opus or Vorbis | Re-encoded to VP9 and Opus |
| AVI, WMV, FLV, 3GP, MPEG | Rarely possible | Re-encoded by the built-in engine |
| GIF | Never | Converted frame by frame |
Changing the resolution or frame rate always means re-encoding.
Choosing the target
- MP4 is the best general choice for phones, editors and uploads: MKV to MP4.
- MOV suits iMovie, Final Cut Pro and QuickTime.
- WEBM is for HTML5 video on websites.
- AVI, WMV, MPEG and 3GP are for old players, DVD equipment and simple phones.
- GIF is for a short silent loop.
- MP3, M4A, FLAC and other audio formats keep only the sound, for example MKV to MP3.
Common MKV problems
The video plays but there is no sound on a phone, TV or in an editor. The MKV probably uses DTS or Dolby sound that the device cannot decode. Converting to MP4 changes the sound to AAC. Subtitles are missing. MP4 and MOV handle subtitle tracks poorly, so do not expect soft subtitles from the MKV to survive the conversion. You can add subtitles again with Add Subtitles. An HEVC file will not convert. Decoding H.265 depends on your browser and graphics hardware. Current Chrome or Edge on a recent PC, or Safari on a Mac, usually work. The file is huge. Blu-ray backups can be 20 GB or more. Converting a very large file needs a lot of free memory and disk space. For a smaller copy, use the MKV compressor. All processing happens in your browser, and your files are never uploaded.