MOS to WebM Converter

How to Convert MOS to WebM Online

1. Upload Your MOS Files: Drag and drop or click "Add Files" to select Leaf / Mamiya MOS RAW captures from an Aptus, Aptus-II, Credo, or Phase One back. Batch is supported — drop in a whole shoot folder so the entire sequence becomes one video.
2. Pick Merge Strategy and Image Duration: Default is Merge Images (every MOS becomes a frame in one WebM). Switch to Video Per Image to render one short clip per RAW. Set Image Duration from 1/60 second (true 60fps timelapse) through 1/30, 1/24, 1/10, 1/5, 1/2, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 seconds per frame — pick 1/24 or 1/30 for a smooth timelapse and 3-5 seconds for a portfolio slideshow.
3. Pick a Codec, Resolution, and Background (Optional): Default codec is VP9 (the modern royalty-free WebM workhorse). Choose AV1 for the smallest output on 2022+ browsers or VP8 for older Android. Pair audio (Opus default, or Vorbis). Pick a resolution preset (4320p / 2160p / 1440p / 1080p / 720p / 480p / 360p / 240p / 144p) or a fixed preset (1920×1080, 1280×720, 3840×2160, vertical 1080×1920 for Reels), enter custom width × height, or scale by percentage — MOS captures are 22-80 MP so you almost always downscale. Set a Background Color (Black, White, and 20+ named colors) for letterboxing when 4:3 medium-format frames don't match a 16:9 video aspect, and tune File Compression with a Quality Preset (Highest → Lowest), File Size %, exact target MB / GB, Constant or Variable Bitrate, or Constant Quality CRF.
4. Convert and Download: Click Convert. Files render in your browser session and download individually or as a ZIP — no sign-up, no watermark, and the original MOS RAWs stay untouched for re-grading later.

Why Convert MOS to WebM?

MOS is the Leaf RAW format used by Mamiya / Leaf / Phase One medium-format digital backs — the Aptus and Aptus-II line (22 MP, 28 MP, 33 MP, 40 MP, 56 MP, 80 MP). It's a TIFF-based container with Lossless JPEG compression that preserves the full sensor data for grading in Capture One, Lightroom, or Photoshop. WebM (VP9 / AV1 video, Opus audio) is the open, royalty-free format Google designed for the web — Chrome, Firefox, Edge, Opera, and Safari 14.1+ play it natively in HTML5 <video>. There's no native video timeline inside a single MOS — converting MOS to WebM means turning a sequence of medium-format RAW stills into a slideshow or timelapse video. Most common reasons:

• Timelapse from a medium-format shoot — Architectural, landscape, and astro photographers leave a Phase One / Aptus on an interval timer. Hundreds of 80 MP MOS frames at 1/24s become a smooth 24fps timelapse — without the 8K master ever leaving your laptop.
• Portfolio reels for client review — A medium-format wedding or fashion set looks better as a slow-cut WebM (3-5 seconds per frame) embedded on the studio website than as a gallery of huge static images that take forever to load.
• Web embedding without YouTube — WebM is the de-facto self-hosted web video container. A <source type="video/webm"> tag plays in every modern browser, and bandwidth costs drop versus shipping the original 80 MP TIFFs.
• Royalty-free distribution — H.264 / H.265 are patent-encumbered. WebM (VP9 / AV1 / VP8 with Opus / Vorbis) has no licensing fees, which matters for paid commercial portfolios, agency reels, and embedded video in apps.
• Background loops and hero sections — A 6-10 second WebM loop made from a few medium-format frames sits behind a hero section at a fraction of the size of a JPEG sequence triggered by JS.
• Sharing a shoot without forcing a Capture One install — Clients and art directors don't have Capture One or Adobe Camera Raw. A single WebM plays in Chrome on any laptop and previews on a phone without third-party software. Pair it with MOS to MP4 when you also need an Apple-friendly fallback.

MOS vs WebM — Format Comparison

Codec and Image Duration Quick Guide

Frequently Asked Questions

Why is the Trim option not available?

There's no existing video timeline in a MOS file — it's a single still — so trim is hidden for image-to-video conversions. Control the WebM length by adjusting Image Duration and the number of MOS files you upload. Total length = number of MOS frames × duration per frame. Sixty MOS frames at 1/24s makes a 2.5-second timelapse; sixty MOS frames at 4 seconds each makes a 4-minute slideshow.

Can I make a smooth timelapse from sequential Leaf / Mamiya captures?

Yes. Set Image Duration to 1/24s (cinematic), 1/30s (standard video), or 1/60s (high-frame-rate web video). Drop the entire interval-timer sequence in alphabetical / capture order and the converter assembles them into a single WebM at that frame rate. For a 10-second 24fps timelapse you need 240 MOS frames; for 30fps, 300 frames; for 60fps, 600 frames.

How does the converter handle 80 MP medium-format resolution?

MOS frames from an Aptus-II 80 are roughly 10328×7760 pixels — far larger than any web video resolution. The converter scales each RAW down to your chosen video resolution preset (commonly 2160p / 4K for showcase work or 1080p for general web use). The 4:3 medium-format aspect doesn't match 16:9 video, so set the Background Color (Black is the typical pick) to letterbox cleanly, or scale to a custom width × height that matches your shoot's native crop.

Should I pick VP9, AV1, or VP8 for WebM output?

VP9 for almost everything — universal modern-browser support, 30-50% smaller than H.264, and fast enough to encode in-browser even on long sequences. AV1 for the smallest file size when your audience is on 2022+ devices; encoding is 5-10× slower but the WebM is roughly half the VP9 size. VP8 only for legacy Android or very old WebM players. For self-hosted web video on a modern site, VP9 is the right default.

Will Safari users be able to play the WebM?

Safari 14.1+ (macOS Big Sur and later, iOS 14.5+) plays WebM with VP9. For older Safari, embed both formats in your <video> tag — WebM first, MP4 fallback second. Modern browsers pick the WebM; older Safari falls back to MP4. Pair this conversion with MOS to MP4 to generate that fallback file.

Does the converter render the RAW data, or do I need to develop the MOS first?

The tool reads the embedded preview / rendered RAW data inside each MOS so you don't need a Capture One step in between. For maximum control over white balance, exposure, lens corrections, and tone, develop your MOS files in Capture One or Lightroom first, export as TIFF or JPEG, and assemble those into the WebM instead — that way the grade is locked in before encoding.

What's the practical limit on number of MOS frames?

Conversion runs in your browser session, so the ceiling is your machine's RAM and how many 30-120 MB RAWs it can hold at once. Most users handle 200-500 MOS frames on a typical laptop; for thousand-frame multi-day timelapses, use a desktop with 16+ GB of RAM and consider rendering in chunks of a few hundred frames, then concatenating. There's no file count limit on the tool itself and no watermark regardless of size.

Can I add music to the slideshow?

The converter focuses on assembling MOS frames into the WebM video stream — it doesn't accept a separate audio track in this flow. Render the silent WebM here, then drop it into iMovie, DaVinci Resolve, Shotcut, or a browser-based editor to add a music track and export the final WebM with Opus audio.