Reverse video playback in iOS

Question

I want to play video backward in AVPlayer. I have tried with changing rates property to -1.0, and although it did work it was not smooth. Is there any way through which I can smoothly play videos backward?

Answer 1

As stated in the comments, the problem is with keyframes and the fact that most codecs are not designed to play backwards. There are 2 options for re-encoding the video that doesn't require you to actually reverse the video in editing.

1. Make every frame a keyframe. I've seen this work well for codecs like H.264 that rely on keyframes. Basically if every frame is a key frame, then each frame can be decoded without relying on any previous frames so it's effectively the same as playing forward.
2. Use a codec that doesn't use keyframes and non-keyframes (basically all frames are always keyframes). PhotoJPEG is one such option, although I'm not completely sure if it plays back on iOS. I would think so. It works great on a Mac.

Note that either of this options will result in larger file sizes compared to typical "keyframe every x frames" encoded video.