[M4IF Technotes] File Type Box Question & Registering ftyp

[Dave Singer]

At 15:30 +0100 12/4/02, Harald Fuchs wrote:
>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?

Um, I am supposed to have an RA running by now.  Mea culpa.
>
>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.

That's not strictly true.  You must have mp41 or mp42 as a compatible 
brand, if you want MPEG-4 compliant readers to expect to be able to 
decode your file.  The major brand might be any other compatible 
specification.  Otherwise what Harald says is both true and helpful. 
We don't let anyone say what must be the major-brand, because then we 
risk not being able to make a file that is decodable by two or more 
standards.  So readers should *always* check only compatible brands.
Why is there a major-brand then?  It identifies what the author 
thought of as the 'best use' of the file, and usually matches the 
file-type, extension, mime-type etc.
>
>
>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
>
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-- 
David Singer
Apple Computer/QuickTime