[Ffmpeg-devel] Re: ffmpeg "wide" atom

Michael Niedermayer michaelni
Wed Aug 23 01:09:42 CEST 2006


On Tue, Aug 22, 2006 at 11:20:29PM +0200, Baptiste Coudurier wrote:
> > furthermore always writing a 64bit mdat will break demuxers which dont
> > understand it
> > 
> > [...]
> And writing 'wide' breaks demuxers which dont understand it either, it
> seems. What is the proportion of demuxers not supporting 'wide' and
> demuxers not supporting 64bit mdat, which is required to demux files >
> 4gb. Also IMHO, creating atoms not existing in specs is doing something
> non standard compliant.
> What should we adopt ? Again I feel lost about policy. 

policy .... well theres no such thing, its more common sense
1. dont break working stuff
2. follow the specs
3. keep things simple, readable and fast
4. dont fix a bug by introducing another bug

but again no policy just my humble oppinion in relation to the subject

> Workaround for
> demuxers ?  There is already a workaround for ipod/mplayer which needs a
> fake 'mp4a' atom in 'wave' one.

iso spec says:
In a number of boxes in this specification, there are two variant forms: version 0 using 32-bit fields, and
version 1 using 64-bit sizes for those same fields. In general, if a version 0 box (32-bit field sizes) can be
used, it should be; version 1 boxes should be used only when the 64-bit field sizes they permit, are required.

furthermore it says:

8.24 Free Space Box
8.24.1 Definition
Box Types:    free, skip
Container:    File or other box
Mandatory:    No
Quantity:     Any number
The contents of a free-space box are irrelevant and may be ignored, or the object deleted, without affecting
the presentation. (Care should be exercised when deleting the object, as this may invalidate the offsets used
in the sample table, unless this object is after all the media data).

so for mov write wide and for mp4 write free or skip

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In the past you could go to a library and read, borrow or copy any book
Today you'd get arrested for mere telling someone where the library is

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