Great for recording, awkward for sharing
MKV (Matroska) is a container that will hold almost anything: any common video codec, several audio tracks, subtitles, chapters, even fonts. It's also tough. If a recording app crashes or the power cuts out, an MKV stays playable up to the last second written, while an unfinished MP4 can be unreadable. That's why so many OBS Studio users record to MKV.
The catch comes afterwards. Phones, social networks, messaging apps and many editors either refuse MKV or handle it badly. MP4 is the format they all expect, so recording in MKV and converting before you edit or upload gives you the best of both.
Copied or re-encoded? It depends on what's inside
Whether the conversion is quick or slow depends on the codecs in your file, not the container. Here's how ClipLime treats the usual suspects:
- H.264, H.265 or AV1 video, copied as is. Most OBS and capture-card recordings fall into this group.
- AAC, MP3 or Dolby Digital (AC-3) audio, copied as is.
- VP9 video, re-encoded as H.264, which takes a while: typically no longer than the video itself.
- Opus, Vorbis or FLAC audio, re-encoded as AAC (192 kbps for stereo), which sounds the same to nearly everyone.
- Uncompressed PCM audio, written by some capture tools, and also turned into AAC.
- DTS audio, most browsers can't decode it, so the converter flags the file before you start.
Want to know in advance? Video Info lists the codecs of any MKV in a second.
From OBS recording to editable MP4
A typical OBS setup records H.264 video with AAC audio, so both streams are copied and even an hour-long session converts in moments. The MP4 has the same quality, and practically the same size, as the MKV.
Recording in H.265 (HEVC) to save space, as newer graphics-card encoders allow? The MP4 keeps that stream as it is, which suits current phones, Macs and browsers. If it must run on an older TV or PC, pick High quality and the picture is re-encoded as H.264.
If you record several audio tracks, game on one, microphone on another, the MP4 keeps a single one: the main track, normally the first, which in a default OBS setup carries the full mix. Hold on to the MKV if you'll want the separate tracks in a multitrack editor later, and play the MP4 through before deleting anything.
From there you can trim the start and end, cut the quiet stretches with the silence remover, or compress a highlight for Discord.
What doesn't come across
- Subtitle tracks, the MP4 contains video and audio only. Keep the MKV, or create fresh captions from the speech with Auto Subtitles.
- Extra audio languages, a second language or commentary track stays behind.
- Chapters and attached fonts: Matroska extras that the MP4 doesn't include.
Very large files need memory: the MP4 is assembled inside your browser before you save it, so a desktop computer with plenty of free RAM handles multi-gigabyte recordings best.