It’s egregious that Apple still doesn’t provide any skip functions in Quicktime. I guess that’s why most people I know — myself included — install IINA or VLC asap.
I would love to be able to skip forward/back by 5sec with a keyboard shortcut in DT built-in video player, which I assume is a derivative of Apple’s unloved player.
Does J-K-L work in the player?
That’s a somewhat standard playback in the QuickTime Player and a lot of editing software.
One L is 1x speed forward
LL is 2x forward
LLL is 5x forward
K is pause
J is 1x speed backward or -1 from the forward speed
KL together is slomo forward
JK together is slomo backward
This script does it.
-- Skip video
property theSeconds : 5
property forward : true
tell application id "DNtp"
try
set theRecord to content record of think window 1
if theRecord = missing value then error "Please open a video record"
set theRecord_Type to (type of theRecord) as string
if theRecord_Type ≠ "quicktime" then error "Please open a video record"
set theTab_CurrentTime to current time of current tab of think window 1
if forward then
set theTime to (theTab_CurrentTime + theSeconds)
set theRecord_Duration to duration of theRecord
if theTime > theRecord_Duration then
set theTime to theRecord_Duration
end if
else
set theTime to (theTab_CurrentTime - theSeconds)
end if
do shell script "open " & (reference URL of theRecord & "?time=" & theTime)
on error error_message number error_number
if the error_number is not -128 then display alert "DEVONthink" message error_message as warning
return
end try
end tell
@cgrunenberg Trying to set the current time directly yields an AppleScript error.
Shift-Left/Right jumps 15 seconds back/forward. There’s even a hidden preference to customize the interval. No need for VLC 
An issue of the script suite, the current time propery should be declared as read-only as it’s obviously not possible to change it.
Anyway, the next release will support this.
Oh thanks @cgrunenberg! That’s exactly what I wanted.
Is there a list of shortcuts for the video player? I’m wondering if there are any other useful ones like changing the playback speed, as that is buried in the media bar menu.
Is it possible to skip forward or backward by pressing the arrow keys without pressing the shift key?
No. Without shift it’s going one frame forward/back.
I think it should be the other way around. The special case here is skipping a frame, so the shift button should be used for that purpose. The default arrow key should be set to 15 seconds. But thanks anyway.