I know that I record by issuing the command
raspivid -o filename.h264 -t 100000 (film for 100 seconds) but how do I specify the directory at witch I want to store the file?
Usb is at
You need to create a directory for and mount the filesystem on the USB drive.
mkdir /mnt/usb mount /dev/sdb1 /mnt/usb
Then you can specify the directory of where the USB drive is now mounted in the same command you issued before, like this:
raspivid -o /mnt/usb/filename.h264 -t 100000