MOS to MKV Converter

MOS to MKV — Which Video Wrapper Should a Leaf RAW Go Into?

A .mos file is the unprocessed RAW capture from a Leaf Aptus medium-format digital back — a very large sensor-level negative meant for editing in Capture One, not for playback. MKV (Matroska) is a modern, open, royalty-free video container. Turning a MOS into an MKV renders the RAW, then holds it as one motionless frame for a duration you set, with no audio. If you only want to see the picture, this is the wrong target — render it to an image instead. When you genuinely need the still inside a video file, the two wrappers worth comparing are MKV and AVI: pick MKV for a current editor or media-server timeline, AVI only when an old Windows tool demands that exact container.

MKV vs AVI for a Still-image Slate

When to Pick MKV

• Your editor, media server, or smart TV is current — MKV is the open, flexible default for H.264 and HEVC, and this converter writes H.264 into the MKV here.
• You may later mux the slate together with other tracks: MKV holds unlimited video, audio, and subtitle tracks plus chapters in one file, where AVI is locked to a single video and audio track.
• You want the smaller, more future-proof file — MKV carries modern codecs (HEVC, AV1) that AVI never supported.

When to Pick AVI Instead

• A specific older Windows editor, capture card, or archive process expects an .avi slate and nothing else.
• The playback target is genuinely ancient hardware — a 2000s DVD player or car head unit — where AVI's reach beats MKV's.
• If either of those is you, use MOS to AVI instead; otherwise MKV is the better-supported choice today.

How to Convert MOS to MKV

1. Upload Your MOS File: Drag and drop your Leaf .mos file onto the page or click "+ Add Files" to browse. You can queue several Aptus or Aptus-II captures at once, though each medium-format RAW can run tens to over a hundred megabytes.
2. Set Duration and Merge images: Open Advanced Options. "Duration" controls how long the still shows — from a single frame (1/60s) up to 10 seconds per frame, with "5 seconds per frame" the default. Use "Merge images" to combine several photos into one MKV, or "Video per image" for a separate file per photo.
3. Pick Quality Preset and Background Color: Keep the "Preset" on "Very High (Recommended)", and set a "Background Color" (Black by default) to fill any letterbox bars where the photo's shape does not match the output frame. Under "Show All Options" the "Video Codec" defaults to H.264, the codec this converter pairs with MKV.
4. Convert and Download: Click "Convert" and download your MKV. No sign-up, no watermark.

Frequently Asked Questions

Is MKV better than AVI for converting a MOS to video?

For almost everyone today, yes. MKV is an open, royalty-free container announced in 2002 — and formally published as RFC 9559 in October 2024 — that carries modern codecs and multiple tracks; AVI is a 1992 Microsoft container limited to one video and one audio stream. Since a MOS produces a single still slate either way, the deciding factor is the destination: MKV suits current editors, Plex/Jellyfin, and smart TVs, while AVI only wins when an old Windows tool or piece of hardware specifically requires that container. If it does, use MOS to AVI.

Which video codec does the MKV output use?

H.264 by default. MKV is a container, not a codec, so it must carry an encoded video stream inside it; for MKV output this converter defaults to H.264, which plays in VLC, modern browsers, and virtually every recent media player. You can switch it under "Show All Options" via the "Video Codec" dropdown, which lists other MKV-compatible choices such as HEVC, VP9, and AV1. Because the source is a still photo, no audio stream is added and the "Audio Codec" option does not appear.

Does the MKV have any motion or sound?

No. From a single MOS, the conversion renders your photo and displays it as one motionless frame for the duration you set — there is no panning, zoom, or animation, and the output carries no audio track. If you upload several photos and choose "Merge images," they play back to back, but each frame is still a static image shown for its set duration, with no transitions between them.

Does the MKV keep the full resolution of a medium-format back?

Not at video dimensions. A Leaf Aptus back captures far more pixels than a standard video frame — well beyond 1080p or even 4K — so fitting the photo into the output resolution downscales it heavily, and most of that medium-format detail is discarded in the video. The frame also inherits H.264's 8-bit color rather than the back's high-bit-depth sensor data. If retaining the resolution matters, render the MOS to a full-size image with MOS to JPG and keep the .mos as your master; an MKV slate is for playback timelines, not for preserving pixel count.

Do I lose the RAW editing latitude when I convert MOS to MKV?

Yes. A MOS stores high-bit-depth linear sensor data, which is why you can recover highlights and shift white balance long after the shot. To put the photo into a video, the converter renders it first — demosaicing the sensor data and baking in white balance, exposure, and tone. Once that rendered frame is inside the MKV, the latitude is gone, exactly as it would be in a JPEG. Keep your original .mos as your editable master in Capture One. Note that MOS comes in uncompressed and compressed variants, and support for the compressed form varies by RAW processor; if a file fails to decode, exporting a TIFF from Capture One first and converting that is the reliable fallback.

Should I really be converting MOS to video at all?

Often not. MOS is the RAW format of Leaf Aptus medium-format backs — Leaf is now a Phase One subsidiary, and its later Credo backs moved to the IIQ format instead — and most people holding a .mos simply want a viewable picture. If that is you, render it to an image with MOS to JPG and keep the .mos as your master; it is far smaller and opens everywhere. Convert to a video wrapper like MKV only when a timeline or media server genuinely needs a video file — a studio slate or a hold frame, for example. For a clip that plays on the widest range of phones and players, MOS to MP4 is the safer video target than either MKV or AVI.

How are my files handled during conversion?

In our testing, a single full-resolution Leaf MOS held for 5 seconds at the "Very High" preset produced a small MKV, since a motionless H.264 frame compresses heavily regardless of the source's pixel count. Your file is uploaded over an encrypted connection, rendered and packaged into MKV on our servers, and deleted automatically a few hours after conversion — no sign-up, no watermark, never shared or made public. The main practical limit is upload size and time, since medium-format MOS files often run from tens to over a hundred megabytes each, not your device.