downloaded file's ext not match the extract_info

[EAFA0]

Here is the bug code.

from youtube_dl import YoutubeDL

video_url = 'https://www.youtube.com/watch?v=XAXwmMu8otM'

ytd_opts = {
    'outtmpl': './%(id)s.%(ext)s'
}

with YoutubeDL(ytd_opts) as ydl:
    info_dict = ydl.extract_info(video_url)

print(info_dict['ext'])

The downloaded file's ext is 'mkv', but the info's ext is 'webm'.

My environment is:

1. ubuntu 16.04
2. python 3.7.4
3. youtube-dl 2020.01.01

Thanks!

[dstftw]

Final ext is not supposed to match.