If you’ve created an .mp4, for example through NCH’s VideoPad Video Editor (Windows) and find that the output doesn’t stream (buffer) through JW Player, then you can download QTIndexSwapper.air (Adobe Integrated Runtime) for Windows here: http://renaun.com/blog/code/qtindexswapper and process your buggy .mp4 files through it. Afterwards streaming/buffering will work fine.