[FFmpeg-devel] Hello,

Jean-Daniel Dupas devlists
Thu Jul 16 21:40:48 CEST 2009

Le 16 juil. 09 ? 21:29, Alex Converse a ?crit :

> On Thu, Jul 16, 2009 at 2:54 PM, Jean-Daniel
> Dupas<devlists at shadowlab.org> wrote:
>> Le 16 juil. 09 ? 20:26, M?ns Rullg?rd a ?crit :
>>> Jean-Daniel Dupas <devlists at shadowlab.org> writes:
>>>> Hello,
>>>> I'm new to this list and to this project. I'm looking to use
>>>> libavformat & libavcodec in some application and would like to
>>>> contribute to improve ffmpeg.
>>>> And so, to try to get into the code, I did a little patch to  
>>>> improve
>>>> alias support in dref in mov files on OS X. This patch uses  
>>>> native Mac
>>>> OS X API to resolve the alias if possible instead of trying to  
>>>> infer
>>>> the path from opaque data.
>>> I'd rather improve our own code if it is incomplete.  Can you
>>> elaborate on what it's missing?
>>> <big elephant in the room> Why native Mac OS X API? </big elephant  
>>> in the
>>> room>
>> I will answer the two questions.
>> First, an alias as defined by the Mac OS File Manager reference is  
>> a blob of
>> "data that is private to the Alias Manager". There is absolutely no
>> guarantee about what it contains. And so, the native API is the  
>> only futur
>> proof and reliable way to resolve it. That why I suggest to use it  
>> when
>> available.
>> [...]
>> I'm not again the idea to improve the actual code to get support for
>> relative path (and maybe inode) (by reverse engineering the content  
>> of the
>> blob), but I thought it would be fine to use the most reliable way  
>> when
>> possible.
> Do you know how QuickTime for Windows deals with such files?
> Also 14496-12:2008 defines dref so it must exist in some sort of
> portable manner. Or is the MOV version of it some sort of crazy
> extended version with lots of Apple specific craziness?
> Also, thanks for your work thus so far.

The QuickTime Library probably contains some function to deal with  
The mpeg 4 standard specify that you should use URL (either relative  
or absolute) in dref elements.
Alias are an Apple extension and so, I don't mind if the Alias support  
is not commit in the trunk. It was just a suggestion.
I never saw an mpeg 4 file with dref/url but if this is (commonly)  
used, it may be worth to implement it.

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