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Proxies are lower-resolution stand-ins for high-resolution media. Masterselects generates them using hardware-accelerated WebCodecs, so you can edit large files smoothly without waiting for full-resolution decoding on every scrub. When you export, the original full-resolution media is always used — proxies are for editing only.

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When to use proxies

Enable proxy generation if you are:
  • Editing 4K or higher footage on a slower machine.
  • Experiencing choppy scrubbing or dropped frames during playback.
  • Working with high-bitrate files that stall the preview.

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Generating a proxy

1

Open a project

Proxies require an open project. Make sure you have saved your work to a project folder first.
2

Right-click a video clip

In the Media Panel, right-click the video file you want to proxy.
3

Select Generate Proxy

Choose Generate Proxy from the context menu. Generation starts immediately in the background — you can keep editing while it runs.
Generation uses a WebCodecs pipeline for maximum speed:
  1. Demuxing — MP4Box parses the container and extracts samples.
  2. Decoding — WebCodecs VideoDecoder runs with hardware acceleration.
  3. Resizing — A pool of 8 OffscreenCanvases resizes frames in parallel.
  4. Encoding — Each canvas independently encodes its frame to JPEG at 82% quality.
Proxies are stored at up to 1280px wide (aspect ratio preserved) at 30 fps.

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Resume and cache indicator

If generation is interrupted — by a browser close, a crash, or by clicking Stop Proxy Generation — it resumes automatically from where it left off the next time you open the project. Already-generated frames are skipped; there is no need to start over. A yellow indicator on the timeline ruler shows which frames are currently cached in the proxy.

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Progress badges

The badge in the Media Panel Name column reflects the current proxy state:
BadgeMeaning
P (blue, solid)Proxy ready
P (filling animation) + X%Generating, with progress
A proxy is considered complete when at least 98% of expected frames are available.

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Switching between proxy and full resolution

Proxy playback mode is separate from proxy generation. To toggle it:
  • Enable Proxy Mode in the toolbar before editing to use the generated proxy frames during playback and scrubbing.
  • Disable Proxy Mode before export to ensure the full-resolution original is used.
When proxy mode is enabled, all video elements in the timeline are replaced by proxy frames. When a proxy frame is missing for a particular position, Masterselects falls back to the original media automatically.

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Storage

Proxies are stored automatically inside your project folder: 
MyProject/
  Proxy/
    {mediaHash}/
      frames/
        000000.jpg
        000001.jpg
        ...
The folder name is a content hash of the first 2MB of the file. If you import the same video twice, both instances share the same proxy — no regeneration needed. To reclaim disk space, delete the Proxy/ folder inside your project directory.

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Warmup

Before starting playback on a proxy-enabled clip, use the Warmup button to preload proxy frames into memory. This prevents any stutter at the beginning of playback when the cache is cold.

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