I noticed that encoding a DNxHD encoded MOV with FFmpeg results in some extra data in the stsd atom for the video track. This data isn't there after encoding to other codecs, say Apple Animation/qtrle for example. At its most basic structure, stsd is 102 bytes, but with DNxHD material is is I think 275 bytes. Furthermore, this data is apparently needed to render the video correctly, because if I truncate stsd to 102, the resulting video is black in the QuickTime player (it still plays in VLC, though). This is some of what I'm seeing (as text): ACLRACLR0001 APRGAPRG0001 ARESARES0001 What is this data and what is referencing it? I have some additional stsd parameters I need to insert, but I don't know if putting stuff in before the "DNxHD extra data" (what we'll call it) will confuse whatever is looking for this extra data. Baptiste?