[openbeos] Re: Implementing MP4
- From: "François Revol" <revol@xxxxxxx>
- To: openbeos@xxxxxxxxxxxxx
- Date: Tue, 05 Jul 2005 14:26:07 +0200 CEST
> >
> > Can't B_MPEG_FORMAT_FAMILY be reused there?
> > I dunno how much MPEG4 differ from MPEG2 & MPEG1, but at least they
> > all share
> > the same MPEG format family links, right?
>
> Possibly but the media_mpeg_description is defined as a single id
> with
> an enumeration
that one is defined for the .mpg format, not for a format using 4CCs.
> but MPEG-4 needs something more like the quicktime one
>
> typedef struct {
> uint32 codec;
> uint32 vendor;
> } media_quicktime_description;
>
> where codec is the quicktime fourcc type and vendor is the vendor
> code
> from the file.
MP4 uses 4CCS just like QT.
There is no reason not to use that, besides, MP4 really is QT
with some twists.
Also, libavformat doesn't have a separate list of 4CCs for mov and mp4.
> Possibly, I am not sure how usefull vendor is but the enum for
> mpeg_id
> would concern me if we started placing codec values in the id.
Usually it's 0. You could try to use '.MP4' to differentiate official
MP4
codes from QT, but I don't think it's useful.
> Does adding something to an enum cause an issue? I think the
no.
> GetMP4FormatFor function would just be a usefull to have but not
> essential since there is a generic MakeFormatFor function. It looks
The Get*FormatFor() are not virtual anyway, so adding them isn't big
deal.
> like there is room in the union for more structs.
Yes.
François.
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