Would be great to have that concurrency option when calling the class

[JenieX]

When generating preview with high rows and cols, it can really eat up the cpu and ram.

[insanity54]

Hi thanks for your issue report. I know it's a year+ later but I'm interested in increasing the performance of Prevvy. Can you give me any information on what you mean by "that concurrency option?" Is concurrency a part of ffmpeg that you know of?