Impossible to download a video from INA website

[ILPlais]

Checklist

• I'm reporting a broken site support
• 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 issues including closed ones

Verbose log

$ youtube-dl --verbose --add-metadata --all-subs --embed-subs --merge-output-format mkv --output "2020-04-02 - s(titre)%.s(ext)%" https://fresques.ina.fr/ouest-en-memoire/fiche-media/Region00509/pevar-estranjour-o-komz-brezhoneg-quatre-etrangers-bretonnants.html
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--verbose', '--add-metadata', '--all-subs', '--embed-subs', '--merge-output-format', 'mkv', '--output', '2020-04-02 - s(titre)%.s(ext)%', 'https://fresques.ina.fr/ouest-en-memoire/fiche-media/Region00509/pevar-estranjour-o-komz-brezhoneg-quatre-etrangers-bretonnants.html']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.03.24
[debug] Python version 3.6.9 (CPython) - Linux-5.3.0-46-generic-x86_64-with-Ubuntu-19.10-eoan
[debug] exe versions: ffmpeg 3.4.6, ffprobe 3.4.6
[debug] Proxy map: {}
[generic] pevar-estranjour-o-komz-brezhoneg-quatre-etrangers-bretonnants: Requesting header
WARNING: Falling back on generic information extractor.
[generic] pevar-estranjour-o-komz-brezhoneg-quatre-etrangers-bretonnants: Downloading webpage
[generic] pevar-estranjour-o-komz-brezhoneg-quatre-etrangers-bretonnants: Extracting information
[generic] Region00509&color=0x0c90b7: Requesting header
[redirect] Following redirect to https://fresques.ina.fr/bundles/hypermediaframeworkjs/widgets/player/flash/playerFB.swf?color=0x0c90b7&url_infos_videos=https%3A%2F%2Ffresques.ina.fr%2Fouest-en-memoire%2Ffiche-media%2Ffb-video%2FRegion00509
[generic] playerFB.swf?color=0x0c90b7&url_infos_videos=https://fresques.ina: Requesting header
WARNING: Falling back on generic information extractor.
[generic] playerFB.swf?color=0x0c90b7&url_infos_videos=https://fresques.ina: Downloading webpage
WARNING: URL could be a direct video link, returning it as such.
[debug] Default format spec: bestvideo+bestaudio/best
ERROR: Error in output template: incomplete format (encoding: 'UTF-8')
Traceback (most recent call last):
  File "/snap/youtube-dl/2840/lib/python3.6/site-packages/youtube_dl/YoutubeDL.py", line 711, in prepare_filename
    filename = expand_path(outtmpl).replace(sep, '') % template_dict
ValueError: incomplete format

Description

Youtube-dl seem to be lost and don't find the correct way to download the video. The video seem to be in SWF by the way.