There are 6 simple steps for rooting Android 7.1.1 for nexus 6:
1 adb reboot bootloader
2 fastboot oem unlock [YES]
3 fastboot flash recovery twrp-3.2.1-0-shamu.img
4 go to recovery
5 adb push .\SuperSU-v2.82-201705271822.zip /sdcard/
6 in recovery install SuperSUfrom sdcard
First of all You should have root on device, second be able to change your partition on android device to status as: writeable (posted few posts ago what is the command for it).
I assume all is set. Now go in adb shell as a root to : /system/media/
When You call to list files, You will get two interesting files:
-rw------- root root 69056 2016-12-26 01:42 bootsamsung.qmg
-rw-r--r-- root root 69056 2016-06-02 17:23 bootsamsungloop.qmg
First is the first static or animating animation, second is the loop. Usually it is like:
-show anoying operator animation
-show after that samsung animation
What to do is to backup first file, and copy the second one but renaming it like the backuped file, which is here “bootsamsung”.
As a result there will be two files as above, but both will do the same animation.