hold the CAPTURE button on the f1 and turn the knob to select the source deck. the CAPTURE button is also a toggle for the capture mode. when you are in capture mode, pressing a sample pad will copy a snippet of (LOOP SIZE) beat length audio from the source.
also, while in capture mode, the knob lets you set a loop and adjust the loop size of the source deck.
with the s4 you only need to press a sample button of the remix deck to copy a snippet from the source. source must be set with mouse though.
Edit: Quotes from the f1 manual:
I left out the auto-capture function.
TRAKTOR KONTROL F1 Reference
4.4.1 Selecting the Capture Source Deck
When capturing Samples into the Remix Deck, you need to designate the capture source Deck:
1. Press and hold the CAPTURE (DELETE) button (you can do this either in Performance
mode or Capture mode).
2. While holding the button, the Display will show the current Source Deck with the letter "c"
followed by the selected Deck name (a, b, c, or d). If you select Loop Recorder, you'll see
"cL" on the Display.
3. Release the CAPTURE (DELETE) button to return the F1 to the previous mode (either Performance or Capture mode).
4.4.2 Activating Capture Mode
To enter and leave Capture mode, press the CAPTURE (DELETE) button, which blinks when
Capture mode is active. In Capture mode, the display will show the Loop Size of the capture
source Deck. The numbers represent the loop length to be captured in beats.
Press CAPTURE (DELETE) to activate Capture mode.
4.4.3 Setting the Capture Size
Once you have activated Capture mode, you can change the capture length with the encoder
► With Capture mode active, rotate the encoder knob to set the capture size.
When pressing the encoder knob at this point, a loop of the specified length will be activated in the capture source Deck. Pressing the encoder knob again will deactivate the loop.
Activating a loop inside the Track Deck before capturing can be handy for transitions between elements of a Remix, or between track transitions in your mix.
4.4.5 Activating a Loop on the Capture Source Deck
► By pressing the encoder knob, you can activate or deactivate the Loop.
When the Loop is active, the Loop Size will blink on and off on the display.
4.4.6 Loop Move and Beat Jump on Capture Source Deck
► By rotating the encoder knob while the Loop is engaged, you change the Loop size by
moving the Loop Out marker. In addition, by holding SHIFT while rotating the encoder
knob, you can move the Loop in increments of the Loop Size.
► With a deactivated loop, by holding SHIFT and rotating the encoder knob you can perform a beat jump in the amount of the Loop Size.
4.4.7 Capturing a Sample into a Cell
Capturing a Sample into a new Sample Cell is very easy:
1. Make sure Capture mode is active (CAPTURE (DELETE) button flashing).
2. If you want the Sample start to snap to the capture source Deck's Beatgrid, make sure the
Snap function (S) is active in the software's Main section. We recommend to always have
the Snap function active when capturing Samples.
3. Press the pad where you want the Sample to be captured to.
You'll see a quick pad animation to confirm that the Sample has been created. If the pad already contained a Sample, the old Sample will be replaced with the new one.
4.4.9 Quick-Capturing Into a Cell
With Quick-capture, you can capture a new Sample with a minimal amount of button presses.
You don't have to switch the F1 into Capture mode with Quick-capture:
1. Press and hold the CAPTURE (DELETE) button.
2. While continuing to hold the CAPTURE (DELETE) button, hit the destination pad.
3. A new Sample will be created on the pad you specified using the capture source Deck's
Loop Size. You'll also see a pad animation, confirming the action.