Do I need to convert 60fps to 30fps so it will be reproducible?

Question

I just bought a GoPro Hero 3 Black Edition. I have been testing out two modes: 1080p at 30fps and 720p at 60fps.

I have noticed that when reproducing the videos with 720p at 60fps they are not really smooth, they seem a little bit weird (I have used VLC to reproduce them). So, a friend of mine suggested me to convert them to 30fps and then they will be slow motion, and later on speed them up 50% with Adobe Premier. After doing that, they look better.

I am confused. Why does this happen? Why do I need to low them down to 30fps and then speed them up up to 50%? Wouldn't that mean that we are back to 60fps?

Thanks

Answer 1

You're not back to 60fps, you're still at 30fps but with every other frame discarded (or blended, or interlaced, depending on how the speedup is accomplished).

When you discard every other frame, you're trading off temporal resolution. If you interlace, you're trading off spatial resolution.

Either way, if this appears smoother, something's wrong with the way the 60fps is being presented. Your playback system may not be able to keep up with the data rate or frame rate. If 1080/30 looks OK, then it's probably not a data rate issue.

Answer 2

My first guess would be that perhaps your screen is incapable of a 60hz refresh. If you have a slower screen refresh or frame rate, then it could result in some odd visual artifacts when trying to view the video at 60fps.

As Jim described, the slowing it to 30fps and then increasing the speed is still a 30fps video, you just discarded half the frames, so that's why it looks like your 30fps shot did. I would look in to the capabilities of your video card and monitor to see if there might be a problem there. Also keep in mind that unless your player supports frame synchronization, it is possible that even a 59 or 60hz screen might be insufficient to play it back if the video isn't loaded in to the buffer by the time the screen goes to refresh. This would result in dropped frames. The same thing can happen at lower frame rates, but if the screen refreshes more often, then the frame still gets displayed, just for a shorter time.