[FFmpeg-devel] [PATCH] mp4 and ipod metadata

[Michael Niedermayer]

On Wed, Jun 11, 2008 at 12:56:29PM -0700, Baptiste Coudurier wrote:
> Michael Niedermayer wrote:
> > On Wed, Jun 11, 2008 at 11:46:47AM -0700, Baptiste Coudurier wrote:
> >> Michael Niedermayer wrote:
> >>> On Wed, Jun 11, 2008 at 02:55:47AM -0700, Baptiste Coudurier wrote:
> >>> [...]
> >>>>> That doesnt mean ipod tags should be in -f mp4 or -f mov but that
> >>>>> there is a -f foobar that contains all tags of all variants. I prefer
> >>>>> if i dont need to have each video 3 times so it can be played on 3
> >>>>> different players.
> >>>> I understand the need, Im afraid it's complicated.
> >>>>
> >>>> Unfortunately, it is so brainded to deal with all iso media variants and
> >>>> their fields having different meaning values that I tend to prefer
> >>>> constraining specific features to specific formats.
> >>>> I think that adding this ipod format was a good thing.
> >>> Could you point at a few examples were fields have different meaning
> >>> between mp4 types (not mp4 vs. mov)?
> >> mp4/3gp channels field in stsd for example, which is reserved to 2 while
> >> in mj2/mov it is actual channels number.
> > 
> > hmm, soo many specs to read and compare :(
> 
> Yes, that was I was saying.

> 
> > [...]
> >
> > So we may have multiple stsd boxes and ones with unknown "codingname" must
> > be ignored.
> 
> Im strongly against created files with 2 stsd.

fine, iam not really suggesting that anyway


> 
> > 
> > ---
> > class AudioSampleEntry(codingname) extends SampleEntry (codingname){
> >    const unsigned int(32)[2] reserved = 0;
> >    template unsigned int(16) channelcount = 2;
>      ^^^^^^^^
> 
> > [...]
> >
> > ...
> > 8.16.3 Semantics
> >     version is an integer that specifies the version of this box
> >     entry_count is an integer that gives the number of entries in the following table
> >     SampleEntry is the appropriate sample entry.
> >     data_reference_index is an integer that contains the index of the data reference to use to retrieve
> >        data associated with samples that use this sample description. Data references are stored in Data
> >        Reference Boxes. The index ranges from 1 to the number of data references.
> >     ChannelCount is either 1 (mono) or 2 (stereo)
> >     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > ---
> > So if i understand the base format does not require ChannelCount to be 2
> > but says=2 in the table
> 
> What if channels are 6 ? This is unclear.

yes, somewhat, but my arguing would be

6 != stereo -> not 2
6 != mono   -> not 1
the count of channels being 6 -> ChannelCount= 6


> 
> > 3gp which is based on the iso base format says reserved_2 for the field but
> > does not say anything about channels. Thus it appears it has been copy and
> > pasted but the description has not.
> >
> > Neither does specify what the word "reserved" means.
> 
> IMHO "reserved" is fixed value.

I do not agree here. "reserved" means 
"set aside for the use of a particular person or party" (first link in google
for definition reserved)

they could have written "fixed" or "constant" if they meant that.
In no specs ive read, reserved meant that one could assume it to
be always that value.


[...]
> Anyway it is not necessary to relaunch this discussion about these
> standards, we already had it many times and it always end badly.

yes, maybe we should do what i suggested mans, simply fork the code
in svn and then each can implement their (de)muxer as they see fit.

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I wish the Xiph folks would stop pretending they've got something they
do not.  Somehow I fear this will remain a wish. -- M?ns Rullg?rd
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