With -crf choose a value between 18 to around 29.

Again, the files may be somewhat large, but you need to make a choice between quality and file size. The good news is that you can create a video that is roughly visually lossless. You can produce a lossless output with libx264, but that will likely create absolutely huge files and may not be decodeable by the browser and/or be supported by JW Player (I've never tried). You're going to have to accept some quality loss Because FFmpeg development is so active it is always recommended that you use the newest version that is practical for you to use. Or you can follow one of the FFmpeg Compile Guides. There are options for Linux, OS X, and Windows. Go to the FFmpeg Download page and get a build there. See the FFmpeg H.264 Video Encoding Guide for more info on that. This is the H.264 video encoder used by ffmepg and, if available, is the default encoder for MP4 output. Use the -crf option instead when encoding with libx264. This means you are using an outdated build.

This option has been removed from FFmpeg a while ago. Do not use -sameq, it does not mean 'same quality'

Convert mp4 to webm ffmpeg