What is the OPDOWNLOAD file format?
A .opdownload file is an incomplete download created by the Opera web browser. It holds the portion of the target file received so far - no format of its own, just the raw bytes transferred up to the point the download stopped or is still running.
.opdownload file creation process
Opera generates an .opdownload file each time a download begins from the internet. Its presence indicates that the download is not yet complete - it is a temporary file that grows as data arrives and exists until the transfer finishes. Once the download completes, Opera removes the .opdownload suffix and renames the file to its proper extension. An .opdownload file will also remain if the download was paused or stopped before finishing. These files are saved in the browser's default download folder.
Recovering data from an .opdownload file
If a download was interrupted before completing, some of the data may still be usable. Removing the .opdownload suffix and replacing it with the file's original extension - for example, renaming video.mp4.opdownload to video.mp4 - allows many applications to attempt to open the partial content. How much is recoverable depends on how far the download had progressed.
Similarities with other browser download formats
.opdownload files share many similarities with analogous formats used by other browsers. Google Chrome and Microsoft Edge use .crdownload for the same purpose; Mozilla Firefox and Apple Safari use .download. All work on the same principle: the in-progress file is written with a temporary suffix and renamed upon completion.
Security & safety
RISK: LOWAn .opdownload file cannot execute and is exactly as risky as the file being downloaded - no more, no less. The suffix actually helps: it stops the OS from treating an incomplete executable as runnable, which is part of its purpose. Two practical notes: if you didn't initiate the download that created the .opdownload, treat the underlying source file as suspicious and delete it; and orphaned .opdownload files left over from old or cancelled downloads are safe to delete to reclaim disk space.
Format details
in a nutshellPrograms that open OPDOWNLOAD files
Windows2 apps
Opera
Free Press Ctrl+J to open Downloads, find the interrupted item and click resume; if it can't resume, click the source link to re-download. 
VLC media player
Open-source For partially downloaded video/audio only: drag the .opdownload into VLC - it plays the portion of an MP4/MKV/MP3 that arrived. 
macOS2 apps
Opera
Free Cmd+J to open Downloads, then resume the interrupted item, or re-download from the source. 
Linux1 app
Technical details
deep spec| Developer | Opera Software |
| Associated browsers | Opera and Opera GX (all current Chromium-based Opera releases on desktop and Android) |
| MIME type | application/octet-stream |
| File encoding | Binary; no wrapper or container - raw downloaded bytes only, identical to the leading portion of the target file |
| File signature (magic bytes) | None of its own; the first bytes match the file type being downloaded (e.g., a partial ZIP begins with the PK signature, a partial JPEG with the JFIF or Exif header) |
| Typical file size | Ranges from 0 bytes (transfer not yet started) up to the full target file size; grows continuously as data arrives |
| Metadata storage | None embedded in the file; Opera tracks download progress and resume state in its internal download manager database, not inside the .opdownload file |
| Compression | None added by Opera; mirrors only whatever compression the target file itself uses |
| Encryption | None added by Opera |
| Supported platforms | Windows, macOS, Linux, Android |
| Equivalent in Chrome and Edge | .crdownload - Opera's Chromium-based engine uses .opdownload instead of the default .crdownload suffix used by Chrome and Edge |
| Naming convention | Target filename with .opdownload appended as a temporary suffix (e.g., setup.exe downloads as setup.exe.opdownload during transfer) |
| On-completion behavior | Opera removes the .opdownload suffix and saves the file under its final name the instant the download finishes; no manual action needed |
| Resume behaviour | If a download is paused or interrupted, Opera can resume from the existing .opdownload file rather than starting over, provided the server supports HTTP range requests |
| Released | Opera 15 (2013), when Opera switched to the Chromium engine; the suffix is Opera's variant of Chromium's .crdownload |
| Latest version | N/A (a temporary suffix, not a versioned format) |
OPDOWNLOAD conversions
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