Updates:
Cc:
fgal...@google.com tomfi...@google.com kqy...@chromium.orgComment #1 on issue 1785 by jz...@
google.com: dash/vp9/isobmff spec does specify what compatible brands to put in the ftyp box (if any)
https://bugs.chromium.org/p/webm/issues/detail?id=1785#c1As it stands now the spec [1], and the dash-if guidelines [2] which reference it, don't mention any and tools like ffmpeg don't write the fourccs as compatible brands.
The inclusion of it in the test file may have been an oversight, but I think registering the brands is in the spirit of what is suggested in 14496-12 [3].
[1]
https://www.webmproject.org/vp9/mp4/[2]
https://dashif.org/docs/DASH-IF-IOP-v4.3.pdf[3]
C.3.2 Usage of the Brand
In order to identify the specifications to which the file complies, brands are used as identifiers in the file format.
These brands are set in the File Type Box. In the File Type Box, two kinds of brands can be indicated. One is
the major_brand that identifies the specification of the best use for the file. Second is the compatible_brands,
which can identify multiple specifications to which the file complies.
For example, a brand might indicate:
(1) the codecs that may be present in the file,
(2) how the data of each codec is stored,
(3) constraints and extensions that are applied to the file.
New brands may be registered if it is necessary to make a new specification that is not fully conformant to the
existing standards. For example, 3GPP allows using AMR and H.263 in the file format. Since these codecs
were not supported in any standards at that time, 3GPP specified the usage of the SampleEntry and template
fields in the ISO Base Media Format as well as defining new boxes to which these codecs refer. Considering
that the file format is used more widely in the future, it is expected that more brands will be needed.