- Posts: 8
- Joined: Tue Aug 27, 2019 12:30 pm
- Real Name: Joe Oberster
Makes 0 difference for final quality etc.
It’s not on by default as you need to predict its size when you start writing file. Old days with slow internet any useless data in-front was causing longer buffering and delayed playback. Today I don’t think this makes any difference as size of that atom for eg. 1h file is way below 1MB if I’m correct. If you work with files stored in eg. S3 then having atom upfront is very useful. I rather would prefer all masters ( not just streaming ones) had it upfront.
Depending on the design having atom upfront may require re-writing file again ( ffmpeg does it this way), so it’s slower and takes 2x space on the disk for some time. Also with atom at the end you can add extra metadata after file been exported. In other case you may simply have no space to add eg. timecode info. Some tools move atom to the end in such a case. If you were to add extra data upfront then file would get broken as there is offset written in that atom which addresses each “frame” within file. You would need to adjust this info in case of adding extra bits at the start of the file ( this is not that easy I think). If atom is at the end you have no such an issue as you changing data after main vide/audio bits ( so you can write as much as you want).