Eliminate black bars

It is meant to be used both ways. For example if a picture was taken in portrait (vertical) it will display best in that orientation and likewise for landscape (horizontal). The bars are called "letterboxing" and "windowboxing" one refers to the bars in landscape and the other in portrait. They appear because the media being displayed is of a different aspect ratio the display. Same thing happens when you watch a widescreen movie with an aspect ratio narrower than 16:9 on your tv, or an older show that is in 4:3 aspect ratio.

Well, I am going to make a few assumptions. One: you have landscape pictures/videos that you're viewing in portrait, and two: you prefer to not to turn your iPhone to landscape orientation.

You may "pinch to zoom" but some content may be cut off, or you could rotate your iPhone to the appropriate orientation. You may have your iPhone's orientation locked, make sure it isn't locked (look in the upper right hand corner of the status bar by the batter for an icon that looks like a circle with an arrow)

One last question, do you use a photography app like "hipstamatic" that might take photos in different aspect ratio than the native camera app?

Otherwise the when viewed in the proper orientation they should appear full screen.

K, remember how I was talking about media with different aspect ratios than the screen they're being viewed on? This is that scenario. You can zoom in, crop to fit your screen, but outside of that there is really nothing you can do.

Ok, I'll be honest I am not that well versed in film editing. I know a few things that might help. First modern tv's use a 16:9 aspect ratio. So you should probably stay away from the 4:3 ratio. Most tvs are also capable of displaying HD content. High definition content is significantly clearer than standard definition (SD). As far as one format being better than another, read this article here http://goarticles.com/article/The-difference-Between-MP4-and-MOV/5705777/

Well, try rotating it to the right orientation, it should work.