My experience is the same as a reviewer below; the files aren't automatically merged, even if I point it to ffmpeg. But this is actually a plus! The DASH_A and DASH_V files are saved separately in my default download directory. So, if I want just audio or video, no need to do anything. And, the ffmpeg command to merge them is straightforward, and because it is a copy, fast and no loss of quality because of demuxing and muxing. e.g. ffmpeg -i file_DASH_A.mp4 -i file_DASH_V.mp4 -c:a copy -c:v copy file.mp4
Perfect!