I've been asked to better explain why we cannot use multiple threads for thumbnail extraction. In addition to what I had written above, let me put it this way: there's nothing much to accelerate, because in most cases, extraction is limited by IO rather than CPU processing. Unlike we did in earlier times, when we did a full decoding of the video to get the images, we are now doing a keyframe based extraction. Keyframes are very easy to decode and we need to decode only those where we want