json Property _filename - please add a property for the actually created filename

[schittli]

Checklist

• I'm reporting a broken site support issue
• I've verified that I'm running youtube-dl version 2020.06.16.1
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar bug reports including closed ones
• I've read bugs section in FAQ

Verbose log

ERROR: youtube-dl.exe : WARNING: Requested formats are incompatible for merge and will be merged into mkv.

Description

It would be great if youtube-dl would return which file was actually created so that the created files could be post-processed.

Normally we can use --print-json and then read the property _filename.
But sometimes youtube-dl has to convert the downloaded file:

ERROR: youtube-dl.exe : WARNING: Requested formats are incompatible for merge and will be merged into mkv.

Then, the JSON property _filename does not reflect this change, and e.g. still displays the -mp4 extension:

_filename            : MyFile - 1920x1080.mp4

As a solution, a separate JSON property could be defined, for example created_filename

Thanks a lot for this great Tool!, it's great to create backups because even in Europe, censorship of harmless content is increasing.

Kind regards,
Thomas