Sometimes YT stop-action single-frame works better with the arrows than at other times. Maybe? it works better when there is a longer time, a pause , between pressing the arrows. ?
Both YT & Vimeo (free) apply compression before they store the videos. I believe that the video is also already compressed when it comes from the Casio cameras. Compression can lose quality with the degree of loss depending on the nature of the compression. Vimeo has a paid service that gives the option to not compress the video and save it just as it was uploaded.
You can also use dropbox to upload and store files including video files for other people to download. Those files are not farther compressed after uploading. Another person can download and play on Quicktime using the arrows with the same quality as you have.
Check out Kinovea for comparing and analyzing videos.