Convert CRDOWNLOAD to MP4

Videos that aren't entirely downloaded could be played by simply renaming the suffix, but in most cases, they will be corrupted with only some playable parts.

Converting a Google Chrome unfinished downloads (.crdownload files) directly to an MP4 video file can be tricky as .crdownload is a temporary file extension used by Google Chrome to indicate an ongoing download. If possible, the easiest way would be to complete the download of the .mp4 file. Once the download is complete, Google Chrome will automatically change the file extension from .crdownload to the correct extension, in this case, .mp4. Unfortunately, it is impossible to recover data easily from this file; however, you can try to recover or convert incomplete downloads using some file recovery or file identification tools. 

Download managers

If possible, the easiest way would be to complete or resume the interrupted download. Once the download is complete, Google Chrome will automatically change the extension from .crdownload to the correct extension, in this case, .mp4. If you have a problem downloading files in Google Chrome, use another web browser or download manager software. They have features to resume interrupted downloads and can be a more reliable way to download large files, especially over unstable internet connections. Various download managers are available for Windows and macOS, each with unique features. Internet Download Manager, Free Download Manager, and JDownloader are the best-known. It is not .crdownload to .mp4 conversion, but you can finish the download another way.

File recovery tools

If completing the download isn't an option, software like Disk Drill or Recuva might help to recover the incomplete file and convert it to a usable format. The success of recovery and conversion might not be guaranteed.

Hex editor, file identification utilities

It is not an easy way for an inexperienced user to attempt to use a hex editor to repair the file manually. This requires a good understanding of file formats and binary file editing. Sometimes, you don't know what file type .crdownlod is, which can help identify the file format from the file header.

Check temporary folders

Sometimes, parts of the file might be stored in temporary folders on your computer. You could check these folders for any parts of the MP4 video file.

Video repair utilities

Some third-party tools claim to repair corrupted or incomplete video files, which might include .crdownload files. Software like Stellar Video Repair could help, although it may not work in every case.

Simply put, it is impossible to convert CRDOWNLOAD to MP4 directly.
Thus, there is no so-called crdownload to mp4 converter or a free online .crdownload to .mp4 converter to be found.