Question:
 “I just watched both of your cider yeast starter videos, I thought they were great, very helpful.  Is it possible to make the yeast starter with the by-products from when you press apples or use a juicer?”
Paraphrased for brevity

Answer:
The process I performed in the videos is one way to create an apple yeast starter when you do not have access to sufficient apples to press or do not have an apple press.

When using an Apple Press, theoretically wild yeast will already be in the resulting juice as it should have been present on the skins of the pressed apples at the start, therefore you shouldn’t need to add additional yeast from anywhere else.  That is of course unless you are looking to produce a specific result such as driving up the ABV (Alcohol By Volume content).  Pressed apple juice is exactly what you need and theoretically all that you need to make hard cider.  If you have insufficient pressed juice to make a full batch of hard cider then you could simply add additional purchased juice once the starter is working.   Bottom line, pressed juice should contain enough natural yeast to start fermentation.

Factors that may affect how well the apple juice actually ferments are many though, i.e. your source of apples, if they have been grown without insecticides, you have not washed off most of the yeast and what varieties of wild yeast happen to be present on them.

Using a juicer may produce the similar results in terms of fermentation.  The resulting mix though may produce quite a different and probably very cloudy cider as juicing liquidizes everything and the resulting mix is quite different from pressed apples.  Most people seem to see a better clearer result from pressing though I personally have not tried producing cider after liquidizing apples.