I need to create a Fragment-MP4 with "sidx" box to create a streamable and seekable video to use it by MediaSource API It is very easy to do it with Bento4 by using "--index" option, but I want to do it with ffmpeg because it has good other options like codec and bitrate and keyframes, It will be hard if I used both (ffmpeg, bento4) to create fmp4 by PHP exec