This app was mentioned in 6 comments, with an average of 2.50 upvotes
If you have an iPhone there is an app called Bike Fast Fit that I read about in one of DC Rainmaker's blogs. I haven't gotten my new bike yet to test it out yet but I figured it was worth a shot for when I start adding bikes to the collection.
For Android I found this one which looks similar but I don't have an Android device to test it.
It's not perfect but there are ios and android apps that work really well. We (me and 4 guys at work) used Roadie Bike Fit on Android and it worked great. We compared it against someone who got a pro bike fit and it confirmed no changes were necessary. My theory is that it gets you really close. I feel soooo much better after using the app. More comfortable and better muscle engagement in my legs on up and down stroke.
Edit: No trainer necessary
GCN is ok, but you need angles as well as measurements. As far as cycling videos go, I like Francis Cade's Bike Fit Tuesdays.
For Android there is Roadie Bike Fit
https://play.google.com/store/apps/details?id=com.mantapix.android.theroadiebikefit
I've been using it for years for quick fixes. Is not perfect but it serves its purpose.
For iOS there is bike fast fit elite. Don't know much about it except that is similar to the Android app.
Just remember that you have to be very accurate with your measurements for the app. Make sure you set up the phone level and as perpendicular as you can get it.
Also, an app is never going to replace a real fit, keep that in mind. And by a real fit, I mean a REAL IBFI fit, a lot of shops will just use the same app you can download off the app store.
It costs a few dollars but I used this app a few weeks ago and it's made a huge difference in power and comfort.
It's not a professional fit but I do not have 300 for a bike fit and this feels great now.
What do you mean 'nope' ?
Don't just make things up if you don't know.
https://www.dcrainmaker.com/2013/10/automated-measurement-review.html
https://blog.bikefit.com/bikefit-pro-app/
https://play.google.com/store/apps/details?id=com.mantapix.android.theroadiebikefit&hl=en_GB