merging with ffmpeg results in --output not fully controlling output filename

[joeyh]

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Description of your issue, suggested solution and other information

When downloading youtube videos with a format that involves merging (including the default bestvideo+bestaudio), and when ffmpeg is used for the merge, --output does not fully control the filename that the merged video is written to. A ".mkv" extension is added to whatever filename --output would generate.

For example, -o out.vid results in:

WARNING: Requested formats are incompatible for merge and will be merged into mkv.
[ffmpeg] Merging formats into "out.vid.mkv"

--get-filename also does not print out the actual filename used in this case.

I was going to use --output to make youtube-dl output to a specific filename in a script; this behavior makes that not practical to do unless I also force the output format to -f best or something like that.

(I have not checked if using avconv for merging also has this behavior.)

[yan12125]

This is a known issue #5710. Sadly currently there's no good solution.

Edit: Should be a duplicate of #7137, not #5710

[joeyh]

I can see the difficulty in making --get-filename work in this situation, but my bug report is primarily about --output not working. It seems to me that for --output, youtube-dl could simply rename the file ffmpeg generates to the filename the user requested.

So, it may be useful to reopen and treat #14864 and #7137 as two separate, though related bugs.

[yan12125]

It seems to me that for --output, youtube-dl could simply rename the file ffmpeg generates to the filename the user requested.

It's not how --output actually works. Indeed its description can be better.

If --get-filename is fixed, your problem is solved, so I point the related issue.

[gabrielgrant]

I'm not sure I follow... it seems like that (making sure the final output is has the file specified filename) is how --output should work, even if it doesn't today. In what circumstances would a user would not want the output contained in the location they've specified?