Does Zubtitle lower the quality of videos?

Videos created by Zubtitle should not be of lesser quality then the original video submitted to Zubtitle for use.

Zubtitle matches the resolution of the original video.  The bitrate of each video will also match the original video or be raised to 8mbs, whichever is higher.

On some occasions if a low quality video is used, typically in the case where the bitrate of the original video is very low, compression artifacts and other issues may be more pronounced with the video created by Zubtitle.  This is because the bitrate of the completed video was raised to 8mbs and may be substantially higher than the original video. In this case, a better quality version of the original video should be used. 

You can check the resolution and bitrate of your original video by looking at the properties of that video on your computer.  In Windows, right-click on that video, select Properties, and then details.  In Mac OS, choose the Info option from the menu bar in Finder.