Screenshot on headless linux machine

[Ortix]

I have a video file of which I want to take several screenshots on my headless debian box. (It's actually a VM).
Currently I'm using this command:

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vlc --vout dummy --rate 1 --video-filter scene --start-time 900 --stop-time 901 --scene-format png --scene-ratio 24 --scene-prefix snap --scene-path ~/ video.mp4

Which gives me a sea of red:

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[0xf5a888] pulse audio output error: PulseAudio server connection failure: Connection refused [0xeae238] main interface error: no suitable interface module [0xe91118] main libvlc error: interface "globalhotkeys,none" initialization failed [0xeae238] dbus interface error: Failed to connect to the D-Bus session daemon: Unable to autolaunch a dbus-daemon without a $DISPLAY for X11 [0xeae238] main interface error: no suitable interface module [0xe91118] main libvlc error: interface "dbus,none" initialization failed [0xe91118] main libvlc: Running vlc with the default interface. Use 'cvlc' to use vlc without interface. [0xeae238] qt4 interface error: Could not connect to X server [0xeae238] skins2 interface error: cannot initialize OSFactory [0xeae238] [cli] lua interface: Listening on host "*console". VLC media player 2.1.5 Rincewind Command Line Interface initialized. Type `help' for help. > ALSA lib confmisc.c:768:(parse_card) cannot find card '0' ALSA lib conf.c:4241:(_snd_config_evaluate) function snd_func_card_driver returned error: No such file or directory ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings ALSA lib conf.c:4241:(_snd_config_evaluate) function snd_func_concat returned error: No such file or directory ALSA lib confmisc.c:1251:(snd_func_refer) error evaluating name ALSA lib conf.c:4241:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory ALSA lib conf.c:4720:(snd_config_expand) Evaluate error: No such file or directory ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM default [0xf5a888] alsa audio output error: cannot open ALSA device "default": No such file or directory [0xf5a888] main audio output error: Audio output failed [0xf5a888] main audio output error: The audio device "default" could not be used: No such file or directory. [0xf5a888] main audio output error: module not functional [0x2ac4668] main decoder error: failed to create audio output

In other words, how would one take screenshots on a linux box without a GUI installed?

[Rémi Denis-Courmont]

Xvfb?

[Ortix]

Xvfb?

Looks interesting, will read upon it a bit more