[M4IF Technotes] File Type Box Question & Registering ftyp

[Harald Fuchs]

On Wednesday 04 December 2023 00:20, Eric Grab wrote:
> We are making MP4 files.  Seems like the right thing to do is have a file
> type box that looks like this for our MPEG-4 files:
>
>   major-brand="divx" (actually the number that represents "divx")
>   minor-version=1
>   compatible-brands="isom","other1","other2",... (and other numbers)
>
> Is this what people are doing when they add file creation tools?
>
> Where does one register for an 'ftyp' to get the official number?

Hello Eric,
the brands identify the file format specification to which the file is 
compatible. The brand names are not meant for private use, new brand names 
are registered with ISO only for file format specifications derived from the 
ISO file format.
If you want to create files compatible with MPEG-4 (.mp4 files) you have to 
use "mp41" or "mp42" as major-brand and at least "isom" as compatible-brand.
I try to explain this in more detail:
The basis for several file formats is the "ISO Media File Format" standardized 
as Amendment 5 of MPEG-4 14496-1:2001 (to become a new separate part of 
MPEG-4: 14496-12) and Amendment 1 of 15444-3 (JPEG 2000).
This file format is not used directly, several specific file formats are 
derived from it like mp4, mj2 (JPEG2000), 3gp. The specific extensions to the 
base file format are standardized separately, for MPEG-4 in Amendment 6 of 
14496-1:2001 (to become a new separate part of MPEG-4: 14496-14).
The ISO Media and the MP4 File Format are currently in the FDIS stage of the 
standardization (the current MPEG internal documents with the text are N5295, 
N5298; I don't know if the are already available at ISO).
Chapter 4.3 of the ISO Media Format (14496-12) describes the file type box, 
chapter 13.15 of the MP4 File Format (14496-14) describes the MPEG-4 specific 
extensions to the file type box. The brand "mp41" is used for files 
compatible with version 1 of the mp4 file format (14496-1:2001) and "mp42" is 
used for files compatible with version 2 (14496-14:2002/3).
Regards,
Harald Fuchs