I'm using YouTube Video and Audio Downloader. Sometimes the audio and video files combine automatically, sometimes they don't - remaining as separate " DASH - .m4a and DASH - .mp4 ". It used to be that when this would happen I could open up a "ffmpeg" window which would allow me to "manually" convert them to a combined .mp4 file. It was a "drag and drop" type of interface. For some reason I can no longer access that ffmpeg combining function. I tried clicking on ffmpeg.exe. I tried re-downloading ffmpeg several times, both from the Downloader options tab and from the ffmpeg website. Thanks for your help.