[youtube] How do you use youtube-dl to download live streams (that are live)?

Some websites with m3u streaming cannot be downloaded in a single youtube-dl step, you can try something like this :

$ URL=https://www.arte.tv/fr/videos/078132-001-A/cosmos-une-odyssee-a-travers-l-univers/
$ youtube-dl -F $URL | grep m3u
HLS_XQ_2     m3u8       1280x720   VA-STA, Allemand 2200k 
HLS_XQ_1     m3u8       1280x720   VF-STF, Français 2200k 
$ CHOSEN_FORMAT=HLS_XQ_1
$ youtube-dl -F "$(youtube-dl -gf $CHOSEN_FORMAT)"
[generic] master: Requesting header
[generic] master: Downloading webpage
[generic] master: Downloading m3u8 information
[info] Available formats for master:
format code  extension  resolution note
61           mp4        audio only   61k , mp4a.40.2
419          mp4        384x216     419k , avc1.66.30, mp4a.40.2
923          mp4        640x360     923k , avc1.77.30, mp4a.40.2
1737         mp4        720x406    1737k , avc1.77.30, mp4a.40.2
2521         mp4        1280x720   2521k , avc1.77.30, mp4a.40.2 (best)
$ youtube-dl --hls-prefer-native -f 1737 "$(youtube-dl -gf $CHOSEN_FORMAT $URL)" -o "$(youtube-dl -f $CHOSEN_FORMAT --get-filename $URL)"
[generic] master: Requesting header
[generic] master: Downloading webpage
[generic] master: Downloading m3u8 information
[hlsnative] Downloading m3u8 manifest
[hlsnative] Total fragments: 257
[download] Destination: Cosmos_une_odyssee_a_travers_l_univers__HLS_XQ_1__078132-001-A.mp4
[download]   0.9% of ~731.27MiB at 624.95KiB/s ETA 13:13
....