Skipped FFmpeg post-processing

[weslenng]

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 --audio-format mp3 --extract-audio --output sample.mp3 -v "https://www.youtube.com/watch?v=dQw4w9WgXcQ"
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--audio-format', 'mp3', '--extract-audio', '--output', 'sample.mp3', '-v', 'https://www.youtube.com/watch?v=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 3.8.2 (CPython) - Linux-5.5.8-arch1-1-x86_64-with-glibc2.2.5
[debug] exe versions: ffmpeg 4.2.2, ffprobe 4.2.2, rtmpdump 2.4
[debug] Proxy map: {}
[youtube] dQw4w9WgXcQ: Downloading webpage
[youtube] {18} signature length 108, html5 player vflset
[youtube] {137} signature length 104, html5 player vflset
[youtube] {248} signature length 104, html5 player vflset
[youtube] {399} signature length 104, html5 player vflset
[youtube] {136} signature length 108, html5 player vflset
[youtube] {247} signature length 104, html5 player vflset
[youtube] {398} signature length 104, html5 player vflset
[youtube] {135} signature length 108, html5 player vflset
[youtube] {244} signature length 104, html5 player vflset
[youtube] {397} signature length 108, html5 player vflset
[youtube] {134} signature length 108, html5 player vflset
[youtube] {243} signature length 108, html5 player vflset
[youtube] {396} signature length 108, html5 player vflset
[youtube] {133} signature length 108, html5 player vflset
[youtube] {242} signature length 108, html5 player vflset
[youtube] {395} signature length 104, html5 player vflset
[youtube] {160} signature length 108, html5 player vflset
[youtube] {278} signature length 108, html5 player vflset
[youtube] {394} signature length 108, html5 player vflset
[youtube] {140} signature length 108, html5 player vflset
[youtube] {249} signature length 108, html5 player vflset
[youtube] {250} signature length 108, html5 player vflset
[youtube] {251} signature length 108, html5 player vflset
[debug] Invoking downloader on 'https://r4---sn-8p8v-bg0l6.googlevideo.com/videoplayback?expire=1587447370&ei=6jGeXvqiBIqixwToxbn4CA&ip=201.95.212.3&id=o-AMU6KHqFkF-Vy_q5t8Jr9ZRa_4qcdE-KVMveHULbZuZu&itag=251&source=youtube&requiressl=yes&mh=7c&mm=31%2C29&mn=sn-8p8v-bg0l6%2Csn-bg07dnlk&ms=au%2Crdu&mv=m&mvi=3&pl=24&gcr=br&initcwndbps=233750&vprv=1&mime=audio%2Fwebm&gir=yes&clen=3438483&dur=212.061&lmt=1578935058552556&mt=1587425683&fvip=4&keepalive=yes&fexp=23882514&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%2Cinitcwndbps&lsig=ALrAebAwRQIhALWq-Fn-DIVQAkNN9s4dI183DpojbOvkl93rZzIyFdg6AiAD_TMvzaQH7-3lAuvj2Gwi11JCmIVA9cmVwWSiyMLKyw%3D%3D&sig=AJpPlLswRgIhAOkKsEcdRnZOZ6UVP7bFpdSEJH7BIvTTJmBP0wsJLYBbAiEAuJe2VreK5kta6nHZA811brlQMdzH9hz0eI33UbxXegM=&ratebypass=yes'
[download] Destination: sample.mp3
[download] 100% of 3.28MiB in 00:00
[debug] ffmpeg command line: ffprobe -show_streams file:sample.mp3
[ffmpeg] Post-process file sample.mp3 exists, skipping

Description

When I pass --output with a hardcoded extension (the same as --audio-format), the post-processing is skipped because the downloaded file has the same name as FFmpeg output

[dstftw]

You must not pass hardcoded extension.