youtube-dl output to stdout not working with format(-f)

[pol4bear]

Checklist

• I'm reporting a broken site support issue
• I've verified that I'm running youtube-dl version 2020.05.29
• 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 -f bestvideo+bestaudio -o - "https://youtube.com/watch?v=TgOu00Mf3kI" 
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '-f', 'bestvideo+bestaudio', '-o', '-', 'https://youtube.com/watch?v=TgOu00Mf3kI']
[debug] Encodings: locale UTF-8, fs utf-8, out utf-8, pref UTF-8
[debug] youtube-dl version 2020.05.29
[debug] Python version 3.8.3 (CPython) - Linux-5.6.15-arch1-1-x86_64-with-glibc2.2.5
[debug] exe versions: ffmpeg 4.2.3, ffprobe 4.2.3, rtmpdump 2.4
[debug] Proxy map: {}
[youtube] TgOu00Mf3kI: Downloading webpage
[youtube] {18} signature length 110, html5 player c31b936c
[youtube] {313} signature length 110, html5 player c31b936c
[youtube] {271} signature length 110, html5 player c31b936c
[youtube] {137} signature length 110, html5 player c31b936c
[youtube] {248} signature length 110, html5 player c31b936c
[youtube] {399} signature length 110, html5 player c31b936c
[youtube] {136} signature length 110, html5 player c31b936c
[youtube] {247} signature length 110, html5 player c31b936c
[youtube] {398} signature length 110, html5 player c31b936c
[youtube] {135} signature length 110, html5 player c31b936c
[youtube] {244} signature length 110, html5 player c31b936c
[youtube] {397} signature length 110, html5 player c31b936c
[youtube] {134} signature length 110, html5 player c31b936c
[youtube] {243} signature length 110, html5 player c31b936c
[youtube] {396} signature length 110, html5 player c31b936c
[youtube] {133} signature length 110, html5 player c31b936c
[youtube] {242} signature length 110, html5 player c31b936c
[youtube] {395} signature length 110, html5 player c31b936c
[youtube] {160} signature length 110, html5 player c31b936c
[youtube] {278} signature length 110, html5 player c31b936c
[youtube] {394} signature length 110, html5 player c31b936c
[youtube] {140} signature length 110, html5 player c31b936c
[youtube] {249} signature length 110, html5 player c31b936c
[youtube] {250} signature length 110, html5 player c31b936c
[youtube] {251} signature length 110, html5 player c31b936c
[debug] Invoking downloader on 'https://r7---sn-3u-bh2se.googlevideo.com/videoplayback?expire=1591370149&ei=RQ3aXsHXGceE1d8Ptr26mAM&ip=222.118.87.225&id=o-AKP2esJkvqTYSKxpc8h1qal51FdU2pehLNF6n2VkGsO3&itag=313&aitags=133%2C134%2C135%2C136%2C137%2C160%2C242%2C243%2C244%2C247%2C248%2C271%2C278%2C313%2C394%2C395%2C396%2C397%2C398%2C399&source=youtube&requiressl=yes&mh=mo&mm=31%2C26&mn=sn-3u-bh2se%2Csn-i3b7knlk&ms=au%2Conr&mv=m&mvi=6&pl=16&initcwndbps=1332500&vprv=1&mime=video%2Fwebm&gir=yes&clen=207767661&dur=221.638&lmt=1588794539461547&mt=1591348478&fvip=2&keepalive=yes&c=WEB&txp=5531432&sparams=expire%2Cei%2Cip%2Cid%2Caitags%2Csource%2Crequiressl%2Cvprv%2Cmime%2Cgir%2Cclen%2Cdur%2Clmt&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Cinitcwndbps&lsig=AG3C_xAwRQIgO5Bc6pjloAlBM48S1BOkcDWZPLr8hVod1MhRXro8XXICIQDq4Gie7u1yxqQ1cRMjXwHZsHtXvsX2AUUQ-R6XoswUjA%3D%3D&sig=AOq0QJ8wRQIhAJ9iN5A1J84QCocKWGLfZdcID50_59WO1IobesCXEOXGAiBfcLfPf_8Ie6oZmGKajWM9Ev2wgLuDJo0Orv1LLzW7WA==&ratebypass=yes'
[download] Destination: -.f313
[download] 100% of 198.14MiB in 00:18
[debug] Invoking downloader on 'https://r7---sn-3u-bh2se.googlevideo.com/videoplayback?expire=1591370149&ei=RQ3aXsHXGceE1d8Ptr26mAM&ip=222.118.87.225&id=o-AKP2esJkvqTYSKxpc8h1qal51FdU2pehLNF6n2VkGsO3&itag=251&source=youtube&requiressl=yes&mh=mo&mm=31%2C26&mn=sn-3u-bh2se%2Csn-i3b7knlk&ms=au%2Conr&mv=m&mvi=6&pl=16&initcwndbps=1332500&vprv=1&mime=audio%2Fwebm&gir=yes&clen=3809571&dur=221.661&lmt=1588789926396200&mt=1591348478&fvip=2&keepalive=yes&c=WEB&txp=5511222&sparams=expire%2Cei%2Cip%2Cid%2Citag%2Csource%2Crequiressl%2Cvprv%2Cmime%2Cgir%2Cclen%2Cdur%2Clmt&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Cinitcwndbps&lsig=AG3C_xAwRgIhAI2Oa3A0KOyqLbGHFqLgfWiukLEDVBQsISlxDHD5X5JIAiEAsdxpPLGyWUSbKHL71I4s8JjocnNmbLK2zCUCfceUjdM%3D&sig=AOq0QJ8wRQIgZC6lv-67FwdLfIb-0J0ENLQbfoTbG70qJdZbat5uRugCIQDwy8mCCqfxiCkxoZ6oRtGHZ6iuxL8ZyqbihBXcqi8zCA==&ratebypass=yes'
[download] Destination: -.f251
[download] 100% of 3.63MiB in 00:00
[ffmpeg] Merging formats into "-.webm"
[debug] ffmpeg command line: ffmpeg -y -loglevel repeat+info -i file:-.f313 -i file:-.f251 -c copy -map 0:v:0 -map 1:a:0 file:-.temp.webm
Deleting original file -.f313 (pass -k to keep)
Deleting original file -.f251 (pass -k to keep)

Description

I'm trying to redirect downloaded file to stdout. I saw that -o - option redirect output to stdout and it worked fine. But if I specify video format like -f "bestvideo+bestaudio" with -o - option it doesn't output to stdout it just download to -.webm.

[dstftw]

You can only redirect media represented by a single file.