[youtube] ffmpeg adds ext when in -o isin't present

[bato3]

Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2018.07.29. If it's not, read this FAQ entry and update. Issues with outdated version will be rejected.

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wrong:

youtube-dl https://www.youtube.com/watch?v=BaW_jenozKc --write-info-json -o "..\test"
[youtube] BaW_jenozKc: Downloading webpage
[youtube] BaW_jenozKc: Downloading video info webpage
[info] Writing video description metadata as JSON to: ..\test.info.json
[download] Destination: ..\test.f137
[download] 100% of 2.11MiB in 00:00
[download] Destination: ..\test.f140
[download] 100% of 154.06KiB in 00:00
[ffmpeg] Merging formats into "..\test.mp4"
Deleting original file ..\test.f137 (pass -k to keep)
Deleting original file ..\test.f140 (pass -k to keep)

OK

youtube-dl https://www.youtube.com/watch?v=BaW_jenozKc --write-info-json -o "..\test2" -f 18
[youtube] BaW_jenozKc: Downloading webpage
[youtube] BaW_jenozKc: Downloading video info webpage
[info] Writing video description metadata as JSON to: ..\test2.info.json
[download] Destination: ..\test2
[download] 100% of 354.29KiB in 00:00

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Description of your issue, suggested solution and other information

In case -o "..\test" ffmpg should merge to file without extension

[dstftw]

This is expected behavior for now.