Just in case this helps in any way to add more detail to my question, the Go Pro 3 is recording in 720 x 50 (W). It's also set as PAL in the Go Pro settings.
All of which makes me think that a project in Premiere Elements 12 should be one of the PAL settings. Or should it be DV instead or something.
Then what happens when you want to send the video from Elements to Vimeo - is that a mother setting again - anyone understand the correct 'workflow' for this kind of thing to get the best results?
I cannot work out what the iPhone 5S records as. There doesn't seem to be anything on the web in the 30 minutes of search I've done that tells you exactly what it is other than it can be 1080 or 720 (but there is no setting on the phone to set that).
Premiere Elements 12 is designed to take control of setting automatically the correct project preset to match the properties of your source media based on the properties of the first file the reaches the Timeline. Sometimes it sets it right, sometimes not. The project preset directs the program to set up the space in the Edit area monitor to correspond to the import's format. When the "sometimes not" situation sets in, then you set the project preset manually before you import media into the project. The following (toward its bottom) gives how to for manually setting the project preset.
What to set? You need to know the properties of your source media.
Example 1. Go Pro 3 is recording in 720 x 50 (W)...I do not under the description as written
My guess is that is 1280 x 720 @ 50 progressive frames per second
If my guess is correct, in Change Settings you use
AVCHD LITE 720p50
Example 2. iPhone 5S
That would probably be 1920 x 1080 @ 30 or 25 progressive frames per second...I am not sure if your iPhone would be using a NTSC or PAL frame rate.
Let us assume NTSC frame rate for now...in Change Settings you use
If you let the project automatically set the project preset and all that it is giving you is 1080i when your video format is not that, then it is definitely time for you
to set the project preset manually.
Lots more to discuss
a. what if you have more than 1 type of format that you want in the project
b, what to do with cell phone video that records with a variable rather than constant frame rate.
If you need to zero in on the properties of your videos and you cannot do that my knowing your recording settings and camera specifications, video
audio properties readout programs can help
Please review and consider. Any questions, please do not hesitate to ask.