I switched from intel-media-va-driver to intel-media-va-driver-non-free and launched these commands (from Can Jasper Lake N6005 use hardware transcoding? - #31 by realEthanZou) :
echo "options i915 enable_guc=2" > /etc/modprobe.d/i915.conf
update-initramfs -u
Now hardware transcoding is working 
