Lightroom is the better option. Import your video into Lightroom. Then in the Library module select the video, and scrub the clip until you get to the frame you want. On the scrubber bar , at the right side are two symbols. A monitor and gear. Click on the monitor. You have two options. Capture frame and Set Poster frame. Click on Capture frame This will put the captured frame next to the video clip in the library. This is saved as a JPEGso you can do the normal Lightroom adjustment in the Develop module if you want. Export as normal