There can be several reasons why your media is not performing well.

1. Media resolution is too high
If you're playing a 4k or otherwise large video file on an older or less powerful computer, the computer can struggle with playing back the video.  Your best solution is to reduce the size of the video.   You can convert your video to improve performance.  See this article for more information: How do I convert videos for InqScribe?  During the conversion you can select a lower resolution like 480p, which is generally good enough for transcribing.
2. Your media is not local
If your media is saved on a network drive or external drive or server somewhere and you have a relatively slow internet connection, InqScribe can have trouble playing and especially rewinding the video.  Moving the video onto your computer's internal hard drive will help. 

3. Movie codec does not support rewind
If you're specifically having trouble with rewind, it could be the codec you're using is not conducive to rewinding.  Movies are compressed with a wide variety of formats and settings, most of which are optimized for playing the movie forward. As a result, playing the movie backwards can be slow. You can transcode the movie to improve rewind performance.  See this article for an example: How do I transcode my video for the best frame-by-frame performance?

4. Too many applications open
Any open applications will eat up some of your computer cycles.  If you're having trouble, rebooting your computer or quitting other applications can sometimes improve performance.