I used ffmpeg to convert an mkv file to mp4 using this command line:
ffmpeg -i input.mkv -c copy file-1.mp4
The resulting mp4 plays fine (video and audio) on Linux Mint's Xplayer. But after uploading file-1, it played with no audio. So I uploaded another mp4 file-2, one I didn't have to convert, and it plays both video and audio without a problem. So whatever's going on with file-1 seems to be with my use of ffmpeg.
The player I'm using is called afterglow. But the HTML5 player handles these two files the same way: file-1 & file-2
Does anyone know why the ffmpeg converted file is soundless when played online? Is there a different conversion command that ensures converted mkv files will play with sound by online players?