Idk what changed in mpv, but whenever I use streamsave now, it seems to only dump the audio to the container, instead of both video and audio. FFProbe says:
[matroska,webm @ 00000000000f3040] Could not find codec parameters for stream 0 (Video: av1 (libdav1d), none, 3840x2160): unspecified pixel format
Consider increasing the value for the 'analyzeduration' (0) and 'probesize' (5000000) options
Idk what changed in mpv, but whenever I use streamsave now, it seems to only dump the audio to the container, instead of both video and audio. FFProbe says: