Incorrect output file name

[bennydictor]

Checklist

• I'm reporting a broken site support issue
• I've verified that I'm running youtube-dl version 2020.03.24
• 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

$ ./youtube-dl -v --format bestvideo+bestaudio/best --prefer-ffmpeg --ffmpeg-location ./ffmpeg --output downloaded_file -- https://youtu.be/dQw4w9WgXcQ
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'--format', u'bestvideo+bestaudio/best', u'--prefer-ffmpeg', u'--ffmpeg-location', u'./ffmpeg', u'--output', u'downloaded_file', u'--', u'https://youtu.be/dQw4w9WgXcQ']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.03.24
[debug] Python version 2.7.17 (CPython) - Linux-4.19.73-15-x86_64-with-Ubuntu-18.04-bionic
[debug] exe versions: ffmpeg 4.2.1-static
[debug] Proxy map: {}
[youtube] dQw4w9WgXcQ: Downloading webpage
[youtube] {18} signature length 102, html5 player vflBAN1y0
[youtube] {137} signature length 106, html5 player vflBAN1y0
[youtube] {248} signature length 106, html5 player vflBAN1y0
[youtube] {136} signature length 106, html5 player vflBAN1y0
[youtube] {247} signature length 102, html5 player vflBAN1y0
[youtube] {398} signature length 106, html5 player vflBAN1y0
[youtube] {135} signature length 102, html5 player vflBAN1y0
[youtube] {244} signature length 106, html5 player vflBAN1y0
[youtube] {397} signature length 106, html5 player vflBAN1y0
[youtube] {134} signature length 102, html5 player vflBAN1y0
[youtube] {243} signature length 106, html5 player vflBAN1y0
[youtube] {396} signature length 106, html5 player vflBAN1y0
[youtube] {133} signature length 106, html5 player vflBAN1y0
[youtube] {242} signature length 102, html5 player vflBAN1y0
[youtube] {395} signature length 106, html5 player vflBAN1y0
[youtube] {160} signature length 106, html5 player vflBAN1y0
[youtube] {278} signature length 106, html5 player vflBAN1y0
[youtube] {394} signature length 106, html5 player vflBAN1y0
[youtube] {140} signature length 106, html5 player vflBAN1y0
[youtube] {249} signature length 102, html5 player vflBAN1y0
[youtube] {250} signature length 106, html5 player vflBAN1y0
[youtube] {251} signature length 106, html5 player vflBAN1y0
WARNING: Requested formats are incompatible for merge and will be merged into mkv.
[debug] Invoking downloader on u'https://r13---sn-n8v7knez.googlevideo.com/videoplayback?expire=1585861986&ei=AgGGXpfAM8-SyQXu9buQDw&ip=2a02%3A6b8%3Ac0a%3A2ba6%3A0%3A47a7%3A96b9%3A0&id=o-AExcRC8xRfQx04hpG6DqFbWg2y2U9Gv_XDpGU2Yhnst7&itag=137&aitags=133%2C134%2C135%2C136%2C137%2C160%2C242%2C243%2C244%2C247%2C248%2C278%2C394%2C395%2C396%2C397%2C398&source=youtube&requiressl=yes&mh=7c&mm=31%2C26&mn=sn-n8v7knez%2Csn-axq7sn7l&ms=au%2Conr&mv=m&mvi=12&pl=47&nh=%2CIgpwcjAyLmxlZDAzKgkxMjcuMC4wLjE&gcr=ru&initcwndbps=1951250&vprv=1&mime=video%2Fmp4&gir=yes&clen=82796547&dur=212.040&lmt=1579453181685841&mt=1585840247&fvip=13&keepalive=yes&c=WEB&txp=5535432&sparams=expire%2Cei%2Cip%2Cid%2Caitags%2Csource%2Crequiressl%2Cgcr%2Cvprv%2Cmime%2Cgir%2Cclen%2Cdur%2Clmt&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Cnh%2Cinitcwndbps&lsig=ALrAebAwRQIgAs4r5q0th-5y2-MOPLYTtrH7nX61rVY7fNr_hz8Cq5ICIQCzVkZ9pr4EDscKVMru2Sl_fwwMYc0UIsaj0FvP2bo3uQ%3D%3D&sig=AJpPlLswRQIgMAVu4EIgdMNza3YI3h97n87AePLbUWyrgQCVZSKqDSwCIQCNQENNkyKIjhHuqKWeDMj76BRf2ylhEDl6Qy1rrFhrMg==&ratebypass=yes'
[download] Destination: downloaded_file.f137
[download] 100% of 78.96MiB in 00:02
[debug] Invoking downloader on u'https://r13---sn-n8v7knez.googlevideo.com/videoplayback?expire=1585861986&ei=AgGGXpfAM8-SyQXu9buQDw&ip=2a02%3A6b8%3Ac0a%3A2ba6%3A0%3A47a7%3A96b9%3A0&id=o-AExcRC8xRfQx04hpG6DqFbWg2y2U9Gv_XDpGU2Yhnst7&itag=251&source=youtube&requiressl=yes&mh=7c&mm=31%2C26&mn=sn-n8v7knez%2Csn-axq7sn7l&ms=au%2Conr&mv=m&mvi=12&pl=47&nh=%2CIgpwcjAyLmxlZDAzKgkxMjcuMC4wLjE&gcr=ru&initcwndbps=1951250&vprv=1&mime=audio%2Fwebm&gir=yes&clen=3438483&dur=212.061&lmt=1578935058552556&mt=1585840247&fvip=13&keepalive=yes&c=WEB&txp=5531432&sparams=expire%2Cei%2Cip%2Cid%2Citag%2Csource%2Crequiressl%2Cgcr%2Cvprv%2Cmime%2Cgir%2Cclen%2Cdur%2Clmt&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Cnh%2Cinitcwndbps&lsig=ALrAebAwRQIgAs4r5q0th-5y2-MOPLYTtrH7nX61rVY7fNr_hz8Cq5ICIQCzVkZ9pr4EDscKVMru2Sl_fwwMYc0UIsaj0FvP2bo3uQ%3D%3D&sig=AJpPlLswRQIhAOuNmKZRu0LphSCbuRuW8d5tkPUfDrs8dAlM3wR_HJvfAiB4Vvuk09Q6S_1t-nG6QTWBgiKyZznvKXyh9AlNTrS-vw==&ratebypass=yes'
[download] Destination: downloaded_file.f251
[download] 100% of 3.28MiB in 00:00
[ffmpeg] Merging formats into "downloaded_file.mkv"
[debug] ffmpeg command line: /home/bennydictor/tmp/ffmpeg -y -loglevel 'repeat+info' -i 'file:downloaded_file.f137' -i 'file:downloaded_file.f251' -c copy -map '0:v:0' -map '1:a:0' 'file:downloaded_file.temp.mkv'
Deleting original file downloaded_file.f137 (pass -k to keep)
Deleting original file downloaded_file.f251 (pass -k to keep)
$ ls
downloaded_file.mkv
ffmpeg
youtube-dl

Description

The value of the --output option is downloaded_file. Expecting the downloaded_file file to appear, but instead downloaded_file.mkv appears.

[dstftw]

You must always specify extension in output template for correct merging.