Not sure about apriltags. But video recording to sdcard with ffmpeg runs at the following speeds:

framerates:

• 30fps @ 640x480
• 20fps @ 1280x720
• 9fps @ 1920x1080

video only:
ffmpeg -f v4l2 -i /dev/video0 -c:v mpeg4 -s 640x480 output4.mp4

with audio like:
ffmpeg -f v4l2 -i /dev/video0 -f alsa -i default -c:v mpeg4 -s 640x480 -c:a aac -ar 44100 -ac 2 -b:a 192k output-x.mp4

h264 and vp8 should be present, but don't work.

Note: the cameras of Unitv2 and UnitV2-M12 are quite different and the latter (M12) has MUCH higher quality! It's not only the lens, also the sensor.

See more at our repo