(Using Windows PowerShell, adapt for UNIX bash shouldn’t be a big issue)

Record a live stream

So something nice with youtube-dl is like you can ask not to download the media but to fetch for the media link :

>> youtube-dl -g http://something
youtube-dl -g https://www.youtube.com/watch?v=RJt01u4yrLQ
https://r2---sn-h0jeened.googlevideo.com/videoplayback?expire=1[...]

If you use that for a twitch channel that is streaming live, it returns you the HLS stream.

>> youtube-dl -g https://www.twitch.tv/farore_de_firone
https://video-weaver.ber01.hls.ttvnw.net/v1/playlist/CpkEQusnrcdffNI3[..]MA2c4.m3u8

It by default binds to the best quality video, but you can check and select all format available using -F

>> youtube-dl -F https://www.twitch.tv/farore_de_firone
[twitch:stream] farore_de_firone: Downloading stream GraphQL
[twitch:stream] farore_de_firone: Downloading access token JSON
[twitch:stream] 39653517372: Downloading m3u8 information
[info] Available formats for 39653517372:
format code       extension  resolution note
audio_only        mp4        audio only    2k , mp4a.40.2
160p              mp4        284x160     230k , avc1.4D401F, 30.0fps, mp4a.40.2
360p              mp4        640x360     630k , avc1.4D401F, 30.0fps, mp4a.40.2
480p              mp4        852x480    1262k , avc1.4D401F, 30.0fps, mp4a.40.2
720p60            mp4        1280x720   3257k , avc1.4D401F, 60.0fps, mp4a.40.2
1080p60__source_  mp4        1920x1080  6713k , avc1.64002A, 60.0fps, mp4a.40.2 (best)

You could even only have the audio-stream

And to select it

>> youtube-dl -f 160p -g https://www.twitch.tv/farore_de_firone

So with this link, you can use ffmpeg to record localy the stream to your computer (and have your own reaplay / VOD without the “disagreement” of Twitch VOD :) )

>> ffmpeg -i "$(youtube-dl -f 720p60 -g https://www.twitch.tv/farore_de_firone)" -c copy stream.20201012.mp4

And here it’s quite simple “dump” of the running script. Nothing prevent you to add some filters, reencoding that adapt to your needs.

Mixing multiple stream

Let’s have some fun, there is some streamers that plays together on the same game. Usually, you can watch their POV at the sametime with the Twitch Squad mechanism or Multitwitch application. But would it be possible to record a file in such way ?

Actually yes, ffmpeg can take multiple video input and transform it on the fly via the filter complex to render all the video on the same stream.

There is a nice topic on Stackoverflow that explain how to simply stack multiple video : https://stackoverflow.com/questions/11552565/vertically-or-horizontally-stack-mosaic-several-videos-using-ffmpeg

Example merging 2 videos :

>> ffmpeg -i "$(youtube-dl -g https://www.twitch.tv/antoinedaniellive)" \
                   -i "$(youtube-dl -g https://www.twitch.tv/soon)" \
                                     -filter_complex vstack=inputs=2 \
                                     -map 0:a \
                                     output.mp4

Example merging 4 videos :

>> ffmpeg -i "$(youtube-dl -f 160p -g https://www.twitch.tv/antoinedaniellive)" \
       -i "$(youtube-dl -f 160p -g https://www.twitch.tv/soon)" \
       -i "$(youtube-dl -f 160p -g https://www.twitch.tv/angledroit )" \
       -i "$(youtube-dl -f 160p -g https://www.twitch.tv/etoiles)" \
       -filter_complex "[0:v][1:v][2:v][3:v]xstack=inputs=4:layout=0_0|w0_0|0_h0|w0_h0[v]"  -map "[v]" \
       -map 0:a \
       -y output.mp4

Note : it’s better to stack video vertically. Horizontal stack does works but then some services (like twitter) won’t accept the video because the image ratio will be too extreme.

The -map 0:a here is necessary to select which audio you want to have.

The format mkv also allow to record multiple video stream within one file that you can selected after that :

>> ffmpeg -i "$(youtube-dl -g https://www.twitch.tv/alphacast)" \ 
             -i "$(youtube-dl -g https://www.twitch.tv/colas_bim)" \
                         -i "$(youtube-dl -g https://www.twitch.tv/eventisfr)" \
                         -i "$(youtube-dl -g https://www.twitch.tv/fusiow)" \
                         -map 0:1 -map 1:1 -map 2:1 -map 3:1 -map 0:0 \ 
                         -c copy \
                         out.mkv