it produces seemingly valid file, but I only can play ot with libaom decoder, not libdav1d (as packaged by termux)
~ $ mpv av1-1.mkv -vo tct --vid=1
(+) Video --vid=1 (av1 160x120 25.000fps)
(+) Audio --aid=1 (vorbis 2ch 48000Hz) Error while decoding frame!
[ffmpeg/video] libdav1d: Error parsing frame header
[ffmpeg/video] libdav1d: Error parsing OBU data
it works if I run it via libaom decoder
mpv av1-1.mkv -vo tct --vid=1 --vd=libaom-av1
(+) Video --vid=1 (av1 160x120 25.000fps)
(+) Audio --aid=1 (vorbis 2ch 48000Hz)
(no errors)