2019-01-09 11:17 GMT+01:00, Ben <bxstover-at-yahoo.co.uk at ffmpeg.org>: > What means "mp3-in-isom"? It means an isom (mp4) file containing mp3. > How do I use an "MP4Box" to remux with ffmpeg? You cannot, MP4Box is a program that allows remuxing to mp4. Carl Eugen